spi: docbook: fix parsing error

[mirror_ubuntu-jammy-kernel.git] / drivers / spi / spi.c

/*
 * SPI init/core code
 *
 * Copyright (C) 2005 David Brownell
 * Copyright (C) 2008 Secret Lab Technologies Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/kernel.h>
#include <linux/device.h>
#include <linux/init.h>
#include <linux/cache.h>
#include <linux/dma-mapping.h>
#include <linux/dmaengine.h>
#include <linux/mutex.h>
#include <linux/of_device.h>
#include <linux/of_irq.h>
#include <linux/clk/clk-conf.h>
#include <linux/slab.h>
#include <linux/mod_devicetable.h>
#include <linux/spi/spi.h>
#include <linux/of_gpio.h>
#include <linux/pm_runtime.h>
#include <linux/pm_domain.h>
#include <linux/export.h>
#include <linux/sched/rt.h>
#include <linux/delay.h>
#include <linux/kthread.h>
#include <linux/ioport.h>
#include <linux/acpi.h>

#define CREATE_TRACE_POINTS
#include <trace/events/spi.h>

static void spidev_release(struct device *dev)
{
        struct spi_device       *spi = to_spi_device(dev);

        /* spi masters may cleanup for released devices */
        if (spi->master->cleanup)
                spi->master->cleanup(spi);

        spi_master_put(spi->master);
        kfree(spi);
}

static ssize_t
modalias_show(struct device *dev, struct device_attribute *a, char *buf)
{
        const struct spi_device *spi = to_spi_device(dev);
        int len;

        len = acpi_device_modalias(dev, buf, PAGE_SIZE - 1);
        if (len != -ENODEV)
                return len;

        return sprintf(buf, "%s%s\n", SPI_MODULE_PREFIX, spi->modalias);
}
static DEVICE_ATTR_RO(modalias);

#define SPI_STATISTICS_ATTRS(field, file)                               \
static ssize_t spi_master_##field##_show(struct device *dev,            \
                                         struct device_attribute *attr, \
                                         char *buf)                     \
{                                                                       \
        struct spi_master *master = container_of(dev,                   \
                                                 struct spi_master, dev); \
        return spi_statistics_##field##_show(&master->statistics, buf); \
}                                                                       \
static struct device_attribute dev_attr_spi_master_##field = {          \
        .attr = { .name = file, .mode = S_IRUGO },                      \
        .show = spi_master_##field##_show,                              \
};                                                                      \
static ssize_t spi_device_##field##_show(struct device *dev,            \
                                         struct device_attribute *attr, \
                                        char *buf)                      \
{                                                                       \
        struct spi_device *spi = to_spi_device(dev);                    \
        return spi_statistics_##field##_show(&spi->statistics, buf);    \
}                                                                       \
static struct device_attribute dev_attr_spi_device_##field = {          \
        .attr = { .name = file, .mode = S_IRUGO },                      \
        .show = spi_device_##field##_show,                              \
}

#define SPI_STATISTICS_SHOW_NAME(name, file, field, format_string)      \
static ssize_t spi_statistics_##name##_show(struct spi_statistics *stat, \
                                            char *buf)                  \
{                                                                       \
        unsigned long flags;                                            \
        ssize_t len;                                                    \
        spin_lock_irqsave(&stat->lock, flags);                          \
        len = sprintf(buf, format_string, stat->field);                 \
        spin_unlock_irqrestore(&stat->lock, flags);                     \
        return len;                                                     \
}                                                                       \
SPI_STATISTICS_ATTRS(name, file)

#define SPI_STATISTICS_SHOW(field, format_string)                       \
        SPI_STATISTICS_SHOW_NAME(field, __stringify(field),             \
                                 field, format_string)

SPI_STATISTICS_SHOW(messages, "%lu");
SPI_STATISTICS_SHOW(transfers, "%lu");
SPI_STATISTICS_SHOW(errors, "%lu");
SPI_STATISTICS_SHOW(timedout, "%lu");

SPI_STATISTICS_SHOW(spi_sync, "%lu");
SPI_STATISTICS_SHOW(spi_sync_immediate, "%lu");
SPI_STATISTICS_SHOW(spi_async, "%lu");

SPI_STATISTICS_SHOW(bytes, "%llu");
SPI_STATISTICS_SHOW(bytes_rx, "%llu");
SPI_STATISTICS_SHOW(bytes_tx, "%llu");

#define SPI_STATISTICS_TRANSFER_BYTES_HISTO(index, number)              \
        SPI_STATISTICS_SHOW_NAME(transfer_bytes_histo##index,           \
                                 "transfer_bytes_histo_" number,        \
                                 transfer_bytes_histo[index],  "%lu")
SPI_STATISTICS_TRANSFER_BYTES_HISTO(0,  "0-1");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(1,  "2-3");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(2,  "4-7");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(3,  "8-15");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(4,  "16-31");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(5,  "32-63");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(6,  "64-127");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(7,  "128-255");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(8,  "256-511");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(9,  "512-1023");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(10, "1024-2047");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(11, "2048-4095");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(12, "4096-8191");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(13, "8192-16383");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(14, "16384-32767");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(15, "32768-65535");
SPI_STATISTICS_TRANSFER_BYTES_HISTO(16, "65536+");

static struct attribute *spi_dev_attrs[] = {
        &dev_attr_modalias.attr,
        NULL,
};

static const struct attribute_group spi_dev_group = {
        .attrs  = spi_dev_attrs,
};

static struct attribute *spi_device_statistics_attrs[] = {
        &dev_attr_spi_device_messages.attr,
        &dev_attr_spi_device_transfers.attr,
        &dev_attr_spi_device_errors.attr,
        &dev_attr_spi_device_timedout.attr,
        &dev_attr_spi_device_spi_sync.attr,
        &dev_attr_spi_device_spi_sync_immediate.attr,
        &dev_attr_spi_device_spi_async.attr,
        &dev_attr_spi_device_bytes.attr,
        &dev_attr_spi_device_bytes_rx.attr,
        &dev_attr_spi_device_bytes_tx.attr,
        &dev_attr_spi_device_transfer_bytes_histo0.attr,
        &dev_attr_spi_device_transfer_bytes_histo1.attr,
        &dev_attr_spi_device_transfer_bytes_histo2.attr,
        &dev_attr_spi_device_transfer_bytes_histo3.attr,
        &dev_attr_spi_device_transfer_bytes_histo4.attr,
        &dev_attr_spi_device_transfer_bytes_histo5.attr,
        &dev_attr_spi_device_transfer_bytes_histo6.attr,
        &dev_attr_spi_device_transfer_bytes_histo7.attr,
        &dev_attr_spi_device_transfer_bytes_histo8.attr,
        &dev_attr_spi_device_transfer_bytes_histo9.attr,
        &dev_attr_spi_device_transfer_bytes_histo10.attr,
        &dev_attr_spi_device_transfer_bytes_histo11.attr,
        &dev_attr_spi_device_transfer_bytes_histo12.attr,
        &dev_attr_spi_device_transfer_bytes_histo13.attr,
        &dev_attr_spi_device_transfer_bytes_histo14.attr,
        &dev_attr_spi_device_transfer_bytes_histo15.attr,
        &dev_attr_spi_device_transfer_bytes_histo16.attr,
        NULL,
};

static const struct attribute_group spi_device_statistics_group = {
        .name  = "statistics",
        .attrs  = spi_device_statistics_attrs,
};

static const struct attribute_group *spi_dev_groups[] = {
        &spi_dev_group,
        &spi_device_statistics_group,
        NULL,
};

static struct attribute *spi_master_statistics_attrs[] = {
        &dev_attr_spi_master_messages.attr,
        &dev_attr_spi_master_transfers.attr,
        &dev_attr_spi_master_errors.attr,
        &dev_attr_spi_master_timedout.attr,
        &dev_attr_spi_master_spi_sync.attr,
        &dev_attr_spi_master_spi_sync_immediate.attr,
        &dev_attr_spi_master_spi_async.attr,
        &dev_attr_spi_master_bytes.attr,
        &dev_attr_spi_master_bytes_rx.attr,
        &dev_attr_spi_master_bytes_tx.attr,
        &dev_attr_spi_master_transfer_bytes_histo0.attr,
        &dev_attr_spi_master_transfer_bytes_histo1.attr,
        &dev_attr_spi_master_transfer_bytes_histo2.attr,
        &dev_attr_spi_master_transfer_bytes_histo3.attr,
        &dev_attr_spi_master_transfer_bytes_histo4.attr,
        &dev_attr_spi_master_transfer_bytes_histo5.attr,
        &dev_attr_spi_master_transfer_bytes_histo6.attr,
        &dev_attr_spi_master_transfer_bytes_histo7.attr,
        &dev_attr_spi_master_transfer_bytes_histo8.attr,
        &dev_attr_spi_master_transfer_bytes_histo9.attr,
        &dev_attr_spi_master_transfer_bytes_histo10.attr,
        &dev_attr_spi_master_transfer_bytes_histo11.attr,
        &dev_attr_spi_master_transfer_bytes_histo12.attr,
        &dev_attr_spi_master_transfer_bytes_histo13.attr,
        &dev_attr_spi_master_transfer_bytes_histo14.attr,
        &dev_attr_spi_master_transfer_bytes_histo15.attr,
        &dev_attr_spi_master_transfer_bytes_histo16.attr,
        NULL,
};

static const struct attribute_group spi_master_statistics_group = {
        .name  = "statistics",
        .attrs  = spi_master_statistics_attrs,
};

static const struct attribute_group *spi_master_groups[] = {
        &spi_master_statistics_group,
        NULL,
};

void spi_statistics_add_transfer_stats(struct spi_statistics *stats,
                                       struct spi_transfer *xfer,
                                       struct spi_master *master)
{
        unsigned long flags;
        int l2len = min(fls(xfer->len), SPI_STATISTICS_HISTO_SIZE) - 1;

        if (l2len < 0)
                l2len = 0;

        spin_lock_irqsave(&stats->lock, flags);

        stats->transfers++;
        stats->transfer_bytes_histo[l2len]++;

        stats->bytes += xfer->len;
        if ((xfer->tx_buf) &&
            (xfer->tx_buf != master->dummy_tx))
                stats->bytes_tx += xfer->len;
        if ((xfer->rx_buf) &&
            (xfer->rx_buf != master->dummy_rx))
                stats->bytes_rx += xfer->len;

        spin_unlock_irqrestore(&stats->lock, flags);
}
EXPORT_SYMBOL_GPL(spi_statistics_add_transfer_stats);

/* modalias support makes "modprobe $MODALIAS" new-style hotplug work,
 * and the sysfs version makes coldplug work too.
 */

static const struct spi_device_id *spi_match_id(const struct spi_device_id *id,
                                                const struct spi_device *sdev)
{
        while (id->name[0]) {
                if (!strcmp(sdev->modalias, id->name))
                        return id;
                id++;
        }
        return NULL;
}

const struct spi_device_id *spi_get_device_id(const struct spi_device *sdev)
{
        const struct spi_driver *sdrv = to_spi_driver(sdev->dev.driver);

        return spi_match_id(sdrv->id_table, sdev);
}
EXPORT_SYMBOL_GPL(spi_get_device_id);

static int spi_match_device(struct device *dev, struct device_driver *drv)
{
        const struct spi_device *spi = to_spi_device(dev);
        const struct spi_driver *sdrv = to_spi_driver(drv);

        /* Attempt an OF style match */
        if (of_driver_match_device(dev, drv))
                return 1;

        /* Then try ACPI */
        if (acpi_driver_match_device(dev, drv))
                return 1;

        if (sdrv->id_table)
                return !!spi_match_id(sdrv->id_table, spi);

        return strcmp(spi->modalias, drv->name) == 0;
}

static int spi_uevent(struct device *dev, struct kobj_uevent_env *env)
{
        const struct spi_device         *spi = to_spi_device(dev);
        int rc;

        rc = acpi_device_uevent_modalias(dev, env);
        if (rc != -ENODEV)
                return rc;

        add_uevent_var(env, "MODALIAS=%s%s", SPI_MODULE_PREFIX, spi->modalias);
        return 0;
}

struct bus_type spi_bus_type = {
        .name           = "spi",
        .dev_groups     = spi_dev_groups,
        .match          = spi_match_device,
        .uevent         = spi_uevent,
};
EXPORT_SYMBOL_GPL(spi_bus_type);


static int spi_drv_probe(struct device *dev)
{
        const struct spi_driver         *sdrv = to_spi_driver(dev->driver);
        struct spi_device               *spi = to_spi_device(dev);
        int ret;

        ret = of_clk_set_defaults(dev->of_node, false);
        if (ret)
                return ret;

        if (dev->of_node) {
                spi->irq = of_irq_get(dev->of_node, 0);
                if (spi->irq == -EPROBE_DEFER)
                        return -EPROBE_DEFER;
                if (spi->irq < 0)
                        spi->irq = 0;
        }

        ret = dev_pm_domain_attach(dev, true);
        if (ret != -EPROBE_DEFER) {
                ret = sdrv->probe(spi);
                if (ret)
                        dev_pm_domain_detach(dev, true);
        }

        return ret;
}

static int spi_drv_remove(struct device *dev)
{
        const struct spi_driver         *sdrv = to_spi_driver(dev->driver);
        int ret;

        ret = sdrv->remove(to_spi_device(dev));
        dev_pm_domain_detach(dev, true);

        return ret;
}

static void spi_drv_shutdown(struct device *dev)
{
        const struct spi_driver         *sdrv = to_spi_driver(dev->driver);

        sdrv->shutdown(to_spi_device(dev));
}

/**
 * __spi_register_driver - register a SPI driver
 * @owner: owner module of the driver to register
 * @sdrv: the driver to register
 * Context: can sleep
 *
 * Return: zero on success, else a negative error code.
 */
int __spi_register_driver(struct module *owner, struct spi_driver *sdrv)
{
        sdrv->driver.owner = owner;
        sdrv->driver.bus = &spi_bus_type;
        if (sdrv->probe)
                sdrv->driver.probe = spi_drv_probe;
        if (sdrv->remove)
                sdrv->driver.remove = spi_drv_remove;
        if (sdrv->shutdown)
                sdrv->driver.shutdown = spi_drv_shutdown;
        return driver_register(&sdrv->driver);
}
EXPORT_SYMBOL_GPL(__spi_register_driver);

/*-------------------------------------------------------------------------*/

/* SPI devices should normally not be created by SPI device drivers; that
 * would make them board-specific.  Similarly with SPI master drivers.
 * Device registration normally goes into like arch/.../mach.../board-YYY.c
 * with other readonly (flashable) information about mainboard devices.
 */

struct boardinfo {
        struct list_head        list;
        struct spi_board_info   board_info;
};

static LIST_HEAD(board_list);
static LIST_HEAD(spi_master_list);

/*
 * Used to protect add/del opertion for board_info list and
 * spi_master list, and their matching process
 */
static DEFINE_MUTEX(board_lock);

/**
 * spi_alloc_device - Allocate a new SPI device
 * @master: Controller to which device is connected
 * Context: can sleep
 *
 * Allows a driver to allocate and initialize a spi_device without
 * registering it immediately.  This allows a driver to directly
 * fill the spi_device with device parameters before calling
 * spi_add_device() on it.
 *
 * Caller is responsible to call spi_add_device() on the returned
 * spi_device structure to add it to the SPI master.  If the caller
 * needs to discard the spi_device without adding it, then it should
 * call spi_dev_put() on it.
 *
 * Return: a pointer to the new device, or NULL.
 */
struct spi_device *spi_alloc_device(struct spi_master *master)
{
        struct spi_device       *spi;

        if (!spi_master_get(master))
                return NULL;

        spi = kzalloc(sizeof(*spi), GFP_KERNEL);
        if (!spi) {
                spi_master_put(master);
                return NULL;
        }

        spi->master = master;
        spi->dev.parent = &master->dev;
        spi->dev.bus = &spi_bus_type;
        spi->dev.release = spidev_release;
        spi->cs_gpio = -ENOENT;

        spin_lock_init(&spi->statistics.lock);

        device_initialize(&spi->dev);
        return spi;
}
EXPORT_SYMBOL_GPL(spi_alloc_device);

static void spi_dev_set_name(struct spi_device *spi)
{
        struct acpi_device *adev = ACPI_COMPANION(&spi->dev);

        if (adev) {
                dev_set_name(&spi->dev, "spi-%s", acpi_dev_name(adev));
                return;
        }

        dev_set_name(&spi->dev, "%s.%u", dev_name(&spi->master->dev),
                     spi->chip_select);
}

static int spi_dev_check(struct device *dev, void *data)
{
        struct spi_device *spi = to_spi_device(dev);
        struct spi_device *new_spi = data;

        if (spi->master == new_spi->master &&
            spi->chip_select == new_spi->chip_select)
                return -EBUSY;
        return 0;
}

/**
 * spi_add_device - Add spi_device allocated with spi_alloc_device
 * @spi: spi_device to register
 *
 * Companion function to spi_alloc_device.  Devices allocated with
 * spi_alloc_device can be added onto the spi bus with this function.
 *
 * Return: 0 on success; negative errno on failure
 */
int spi_add_device(struct spi_device *spi)
{
        static DEFINE_MUTEX(spi_add_lock);
        struct spi_master *master = spi->master;
        struct device *dev = master->dev.parent;
        int status;

        /* Chipselects are numbered 0..max; validate. */
        if (spi->chip_select >= master->num_chipselect) {
                dev_err(dev, "cs%d >= max %d\n",
                        spi->chip_select,
                        master->num_chipselect);
                return -EINVAL;
        }

        /* Set the bus ID string */
        spi_dev_set_name(spi);

        /* We need to make sure there's no other device with this
         * chipselect **BEFORE** we call setup(), else we'll trash
         * its configuration.  Lock against concurrent add() calls.
         */
        mutex_lock(&spi_add_lock);

        status = bus_for_each_dev(&spi_bus_type, NULL, spi, spi_dev_check);
        if (status) {
                dev_err(dev, "chipselect %d already in use\n",
                                spi->chip_select);
                goto done;
        }

        if (master->cs_gpios)
                spi->cs_gpio = master->cs_gpios[spi->chip_select];

        /* Drivers may modify this initial i/o setup, but will
         * normally rely on the device being setup.  Devices
         * using SPI_CS_HIGH can't coexist well otherwise...
         */
        status = spi_setup(spi);
        if (status < 0) {
                dev_err(dev, "can't setup %s, status %d\n",
                                dev_name(&spi->dev), status);
                goto done;
        }

        /* Device may be bound to an active driver when this returns */
        status = device_add(&spi->dev);
        if (status < 0)
                dev_err(dev, "can't add %s, status %d\n",
                                dev_name(&spi->dev), status);
        else
                dev_dbg(dev, "registered child %s\n", dev_name(&spi->dev));

done:
        mutex_unlock(&spi_add_lock);
        return status;
}
EXPORT_SYMBOL_GPL(spi_add_device);

/**
 * spi_new_device - instantiate one new SPI device
 * @master: Controller to which device is connected
 * @chip: Describes the SPI device
 * Context: can sleep
 *
 * On typical mainboards, this is purely internal; and it's not needed
 * after board init creates the hard-wired devices.  Some development
 * platforms may not be able to use spi_register_board_info though, and
 * this is exported so that for example a USB or parport based adapter
 * driver could add devices (which it would learn about out-of-band).
 *
 * Return: the new device, or NULL.
 */
struct spi_device *spi_new_device(struct spi_master *master,
                                  struct spi_board_info *chip)
{
        struct spi_device       *proxy;
        int                     status;

        /* NOTE:  caller did any chip->bus_num checks necessary.
         *
         * Also, unless we change the return value convention to use
         * error-or-pointer (not NULL-or-pointer), troubleshootability
         * suggests syslogged diagnostics are best here (ugh).
         */

        proxy = spi_alloc_device(master);
        if (!proxy)
                return NULL;

        WARN_ON(strlen(chip->modalias) >= sizeof(proxy->modalias));

        proxy->chip_select = chip->chip_select;
        proxy->max_speed_hz = chip->max_speed_hz;
        proxy->mode = chip->mode;
        proxy->irq = chip->irq;
        strlcpy(proxy->modalias, chip->modalias, sizeof(proxy->modalias));
        proxy->dev.platform_data = (void *) chip->platform_data;
        proxy->controller_data = chip->controller_data;
        proxy->controller_state = NULL;

        status = spi_add_device(proxy);
        if (status < 0) {
                spi_dev_put(proxy);
                return NULL;
        }

        return proxy;
}
EXPORT_SYMBOL_GPL(spi_new_device);

/**
 * spi_unregister_device - unregister a single SPI device
 * @spi: spi_device to unregister
 *
 * Start making the passed SPI device vanish. Normally this would be handled
 * by spi_unregister_master().
 */
void spi_unregister_device(struct spi_device *spi)
{
        if (!spi)
                return;

        if (spi->dev.of_node)
                of_node_clear_flag(spi->dev.of_node, OF_POPULATED);
        device_unregister(&spi->dev);
}
EXPORT_SYMBOL_GPL(spi_unregister_device);

static void spi_match_master_to_boardinfo(struct spi_master *master,
                                struct spi_board_info *bi)
{
        struct spi_device *dev;

        if (master->bus_num != bi->bus_num)
                return;

        dev = spi_new_device(master, bi);
        if (!dev)
                dev_err(master->dev.parent, "can't create new device for %s\n",
                        bi->modalias);
}

/**
 * spi_register_board_info - register SPI devices for a given board
 * @info: array of chip descriptors
 * @n: how many descriptors are provided
 * Context: can sleep
 *
 * Board-specific early init code calls this (probably during arch_initcall)
 * with segments of the SPI device table.  Any device nodes are created later,
 * after the relevant parent SPI controller (bus_num) is defined.  We keep
 * this table of devices forever, so that reloading a controller driver will
 * not make Linux forget about these hard-wired devices.
 *
 * Other code can also call this, e.g. a particular add-on board might provide
 * SPI devices through its expansion connector, so code initializing that board
 * would naturally declare its SPI devices.
 *
 * The board info passed can safely be __initdata ... but be careful of
 * any embedded pointers (platform_data, etc), they're copied as-is.
 *
 * Return: zero on success, else a negative error code.
 */
int spi_register_board_info(struct spi_board_info const *info, unsigned n)
{
        struct boardinfo *bi;
        int i;

        if (!n)
                return -EINVAL;

        bi = kzalloc(n * sizeof(*bi), GFP_KERNEL);
        if (!bi)
                return -ENOMEM;

        for (i = 0; i < n; i++, bi++, info++) {
                struct spi_master *master;

                memcpy(&bi->board_info, info, sizeof(*info));
                mutex_lock(&board_lock);
                list_add_tail(&bi->list, &board_list);
                list_for_each_entry(master, &spi_master_list, list)
                        spi_match_master_to_boardinfo(master, &bi->board_info);
                mutex_unlock(&board_lock);
        }

        return 0;
}

/*-------------------------------------------------------------------------*/

static void spi_set_cs(struct spi_device *spi, bool enable)
{
        if (spi->mode & SPI_CS_HIGH)
                enable = !enable;

        if (gpio_is_valid(spi->cs_gpio))
                gpio_set_value(spi->cs_gpio, !enable);
        else if (spi->master->set_cs)
                spi->master->set_cs(spi, !enable);
}

#ifdef CONFIG_HAS_DMA
static int spi_map_buf(struct spi_master *master, struct device *dev,
                       struct sg_table *sgt, void *buf, size_t len,
                       enum dma_data_direction dir)
{
        const bool vmalloced_buf = is_vmalloc_addr(buf);
        int desc_len;
        int sgs;
        struct page *vm_page;
        void *sg_buf;
        size_t min;
        int i, ret;

        if (vmalloced_buf) {
                desc_len = PAGE_SIZE;
                sgs = DIV_ROUND_UP(len + offset_in_page(buf), desc_len);
        } else {
                desc_len = master->max_dma_len;
                sgs = DIV_ROUND_UP(len, desc_len);
        }

        ret = sg_alloc_table(sgt, sgs, GFP_KERNEL);
        if (ret != 0)
                return ret;

        for (i = 0; i < sgs; i++) {

                if (vmalloced_buf) {
                        min = min_t(size_t,
                                    len, desc_len - offset_in_page(buf));
                        vm_page = vmalloc_to_page(buf);
                        if (!vm_page) {
                                sg_free_table(sgt);
                                return -ENOMEM;
                        }
                        sg_set_page(&sgt->sgl[i], vm_page,
                                    min, offset_in_page(buf));
                } else {
                        min = min_t(size_t, len, desc_len);
                        sg_buf = buf;
                        sg_set_buf(&sgt->sgl[i], sg_buf, min);
                }


                buf += min;
                len -= min;
        }

        ret = dma_map_sg(dev, sgt->sgl, sgt->nents, dir);
        if (!ret)
                ret = -ENOMEM;
        if (ret < 0) {
                sg_free_table(sgt);
                return ret;
        }

        sgt->nents = ret;

        return 0;
}

static void spi_unmap_buf(struct spi_master *master, struct device *dev,
                          struct sg_table *sgt, enum dma_data_direction dir)
{
        if (sgt->orig_nents) {
                dma_unmap_sg(dev, sgt->sgl, sgt->orig_nents, dir);
                sg_free_table(sgt);
        }
}

static int __spi_map_msg(struct spi_master *master, struct spi_message *msg)
{
        struct device *tx_dev, *rx_dev;
        struct spi_transfer *xfer;
        int ret;

        if (!master->can_dma)
                return 0;

        if (master->dma_tx)
                tx_dev = master->dma_tx->device->dev;
        else
                tx_dev = &master->dev;

        if (master->dma_rx)
                rx_dev = master->dma_rx->device->dev;
        else
                rx_dev = &master->dev;

        list_for_each_entry(xfer, &msg->transfers, transfer_list) {
                if (!master->can_dma(master, msg->spi, xfer))
                        continue;

                if (xfer->tx_buf != NULL) {
                        ret = spi_map_buf(master, tx_dev, &xfer->tx_sg,
                                          (void *)xfer->tx_buf, xfer->len,
                                          DMA_TO_DEVICE);
                        if (ret != 0)
                                return ret;
                }

                if (xfer->rx_buf != NULL) {
                        ret = spi_map_buf(master, rx_dev, &xfer->rx_sg,
                                          xfer->rx_buf, xfer->len,
                                          DMA_FROM_DEVICE);
                        if (ret != 0) {
                                spi_unmap_buf(master, tx_dev, &xfer->tx_sg,
                                              DMA_TO_DEVICE);
                                return ret;
                        }
                }
        }

        master->cur_msg_mapped = true;

        return 0;
}

static int __spi_unmap_msg(struct spi_master *master, struct spi_message *msg)
{
        struct spi_transfer *xfer;
        struct device *tx_dev, *rx_dev;

        if (!master->cur_msg_mapped || !master->can_dma)
                return 0;

        if (master->dma_tx)
                tx_dev = master->dma_tx->device->dev;
        else
                tx_dev = &master->dev;

        if (master->dma_rx)
                rx_dev = master->dma_rx->device->dev;
        else
                rx_dev = &master->dev;

        list_for_each_entry(xfer, &msg->transfers, transfer_list) {
                if (!master->can_dma(master, msg->spi, xfer))
                        continue;

                spi_unmap_buf(master, rx_dev, &xfer->rx_sg, DMA_FROM_DEVICE);
                spi_unmap_buf(master, tx_dev, &xfer->tx_sg, DMA_TO_DEVICE);
        }

        return 0;
}
#else /* !CONFIG_HAS_DMA */
static inline int __spi_map_msg(struct spi_master *master,
                                struct spi_message *msg)
{
        return 0;
}

static inline int __spi_unmap_msg(struct spi_master *master,
                                  struct spi_message *msg)
{
        return 0;
}
#endif /* !CONFIG_HAS_DMA */

static inline int spi_unmap_msg(struct spi_master *master,
                                struct spi_message *msg)
{
        struct spi_transfer *xfer;

        list_for_each_entry(xfer, &msg->transfers, transfer_list) {
                /*
                 * Restore the original value of tx_buf or rx_buf if they are
                 * NULL.
                 */
                if (xfer->tx_buf == master->dummy_tx)
                        xfer->tx_buf = NULL;
                if (xfer->rx_buf == master->dummy_rx)
                        xfer->rx_buf = NULL;
        }

        return __spi_unmap_msg(master, msg);
}

static int spi_map_msg(struct spi_master *master, struct spi_message *msg)
{
        struct spi_transfer *xfer;
        void *tmp;
        unsigned int max_tx, max_rx;

        if (master->flags & (SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX)) {
                max_tx = 0;
                max_rx = 0;

                list_for_each_entry(xfer, &msg->transfers, transfer_list) {
                        if ((master->flags & SPI_MASTER_MUST_TX) &&
                            !xfer->tx_buf)
                                max_tx = max(xfer->len, max_tx);
                        if ((master->flags & SPI_MASTER_MUST_RX) &&
                            !xfer->rx_buf)
                                max_rx = max(xfer->len, max_rx);
                }

                if (max_tx) {
                        tmp = krealloc(master->dummy_tx, max_tx,
                                       GFP_KERNEL | GFP_DMA);
                        if (!tmp)
                                return -ENOMEM;
                        master->dummy_tx = tmp;
                        memset(tmp, 0, max_tx);
                }

                if (max_rx) {
                        tmp = krealloc(master->dummy_rx, max_rx,
                                       GFP_KERNEL | GFP_DMA);
                        if (!tmp)
                                return -ENOMEM;
                        master->dummy_rx = tmp;
                }

                if (max_tx || max_rx) {
                        list_for_each_entry(xfer, &msg->transfers,
                                            transfer_list) {
                                if (!xfer->tx_buf)
                                        xfer->tx_buf = master->dummy_tx;
                                if (!xfer->rx_buf)
                                        xfer->rx_buf = master->dummy_rx;
                        }
                }
        }

        return __spi_map_msg(master, msg);
}

/*
 * spi_transfer_one_message - Default implementation of transfer_one_message()
 *
 * This is a standard implementation of transfer_one_message() for
 * drivers which impelment a transfer_one() operation.  It provides
 * standard handling of delays and chip select management.
 */
static int spi_transfer_one_message(struct spi_master *master,
                                    struct spi_message *msg)
{
        struct spi_transfer *xfer;
        bool keep_cs = false;
        int ret = 0;
        unsigned long ms = 1;
        struct spi_statistics *statm = &master->statistics;
        struct spi_statistics *stats = &msg->spi->statistics;

        spi_set_cs(msg->spi, true);

        SPI_STATISTICS_INCREMENT_FIELD(statm, messages);
        SPI_STATISTICS_INCREMENT_FIELD(stats, messages);

        list_for_each_entry(xfer, &msg->transfers, transfer_list) {
                trace_spi_transfer_start(msg, xfer);

                spi_statistics_add_transfer_stats(statm, xfer, master);
                spi_statistics_add_transfer_stats(stats, xfer, master);

                if (xfer->tx_buf || xfer->rx_buf) {
                        reinit_completion(&master->xfer_completion);

                        ret = master->transfer_one(master, msg->spi, xfer);
                        if (ret < 0) {
                                SPI_STATISTICS_INCREMENT_FIELD(statm,
                                                               errors);
                                SPI_STATISTICS_INCREMENT_FIELD(stats,
                                                               errors);
                                dev_err(&msg->spi->dev,
                                        "SPI transfer failed: %d\n", ret);
                                goto out;
                        }

                        if (ret > 0) {
                                ret = 0;
                                ms = xfer->len * 8 * 1000 / xfer->speed_hz;
                                ms += ms + 100; /* some tolerance */

                                ms = wait_for_completion_timeout(&master->xfer_completion,
                                                                 msecs_to_jiffies(ms));
                        }

                        if (ms == 0) {
                                SPI_STATISTICS_INCREMENT_FIELD(statm,
                                                               timedout);
                                SPI_STATISTICS_INCREMENT_FIELD(stats,
                                                               timedout);
                                dev_err(&msg->spi->dev,
                                        "SPI transfer timed out\n");
                                msg->status = -ETIMEDOUT;
                        }
                } else {
                        if (xfer->len)
                                dev_err(&msg->spi->dev,
                                        "Bufferless transfer has length %u\n",
                                        xfer->len);
                }

                trace_spi_transfer_stop(msg, xfer);

                if (msg->status != -EINPROGRESS)
                        goto out;

                if (xfer->delay_usecs)
                        udelay(xfer->delay_usecs);

                if (xfer->cs_change) {
                        if (list_is_last(&xfer->transfer_list,
                                         &msg->transfers)) {
                                keep_cs = true;
                        } else {
                                spi_set_cs(msg->spi, false);
                                udelay(10);
                                spi_set_cs(msg->spi, true);
                        }
                }

                msg->actual_length += xfer->len;
        }

out:
        if (ret != 0 || !keep_cs)
                spi_set_cs(msg->spi, false);

        if (msg->status == -EINPROGRESS)
                msg->status = ret;

        if (msg->status && master->handle_err)
                master->handle_err(master, msg);

        spi_res_release(master, msg);

        spi_finalize_current_message(master);

        return ret;
}

/**
 * spi_finalize_current_transfer - report completion of a transfer
 * @master: the master reporting completion
 *
 * Called by SPI drivers using the core transfer_one_message()
 * implementation to notify it that the current interrupt driven
 * transfer has finished and the next one may be scheduled.
 */
void spi_finalize_current_transfer(struct spi_master *master)
{
        complete(&master->xfer_completion);
}
EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);

/**
 * __spi_pump_messages - function which processes spi message queue
 * @master: master to process queue for
 * @in_kthread: true if we are in the context of the message pump thread
 *
 * This function checks if there is any spi message in the queue that
 * needs processing and if so call out to the driver to initialize hardware
 * and transfer each message.
 *
 * Note that it is called both from the kthread itself and also from
 * inside spi_sync(); the queue extraction handling at the top of the
 * function should deal with this safely.
 */
static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
{
        unsigned long flags;
        bool was_busy = false;
        int ret;

        /* Lock queue */
        spin_lock_irqsave(&master->queue_lock, flags);

        /* Make sure we are not already running a message */
        if (master->cur_msg) {
                spin_unlock_irqrestore(&master->queue_lock, flags);
                return;
        }

        /* If another context is idling the device then defer */
        if (master->idling) {
                queue_kthread_work(&master->kworker, &master->pump_messages);
                spin_unlock_irqrestore(&master->queue_lock, flags);
                return;
        }

        /* Check if the queue is idle */
        if (list_empty(&master->queue) || !master->running) {
                if (!master->busy) {
                        spin_unlock_irqrestore(&master->queue_lock, flags);
                        return;
                }

                /* Only do teardown in the thread */
                if (!in_kthread) {
                        queue_kthread_work(&master->kworker,
                                           &master->pump_messages);
                        spin_unlock_irqrestore(&master->queue_lock, flags);
                        return;
                }

                master->busy = false;
                master->idling = true;
                spin_unlock_irqrestore(&master->queue_lock, flags);

                kfree(master->dummy_rx);
                master->dummy_rx = NULL;
                kfree(master->dummy_tx);
                master->dummy_tx = NULL;
                if (master->unprepare_transfer_hardware &&
                    master->unprepare_transfer_hardware(master))
                        dev_err(&master->dev,
                                "failed to unprepare transfer hardware\n");
                if (master->auto_runtime_pm) {
                        pm_runtime_mark_last_busy(master->dev.parent);
                        pm_runtime_put_autosuspend(master->dev.parent);
                }
                trace_spi_master_idle(master);

                spin_lock_irqsave(&master->queue_lock, flags);
                master->idling = false;
                spin_unlock_irqrestore(&master->queue_lock, flags);
                return;
        }

        /* Extract head of queue */
        master->cur_msg =
                list_first_entry(&master->queue, struct spi_message, queue);

        list_del_init(&master->cur_msg->queue);
        if (master->busy)
                was_busy = true;
        else
                master->busy = true;
        spin_unlock_irqrestore(&master->queue_lock, flags);

        if (!was_busy && master->auto_runtime_pm) {
                ret = pm_runtime_get_sync(master->dev.parent);
                if (ret < 0) {
                        dev_err(&master->dev, "Failed to power device: %d\n",
                                ret);
                        return;
                }
        }

        if (!was_busy)
                trace_spi_master_busy(master);

        if (!was_busy && master->prepare_transfer_hardware) {
                ret = master->prepare_transfer_hardware(master);
                if (ret) {
                        dev_err(&master->dev,
                                "failed to prepare transfer hardware\n");

                        if (master->auto_runtime_pm)
                                pm_runtime_put(master->dev.parent);
                        return;
                }
        }

        trace_spi_message_start(master->cur_msg);

        if (master->prepare_message) {
                ret = master->prepare_message(master, master->cur_msg);
                if (ret) {
                        dev_err(&master->dev,
                                "failed to prepare message: %d\n", ret);
                        master->cur_msg->status = ret;
                        spi_finalize_current_message(master);
                        return;
                }
                master->cur_msg_prepared = true;
        }

        ret = spi_map_msg(master, master->cur_msg);
        if (ret) {
                master->cur_msg->status = ret;
                spi_finalize_current_message(master);
                return;
        }

        ret = master->transfer_one_message(master, master->cur_msg);
        if (ret) {
                dev_err(&master->dev,
                        "failed to transfer one message from queue\n");
                return;
        }
}

/**
 * spi_pump_messages - kthread work function which processes spi message queue
 * @work: pointer to kthread work struct contained in the master struct
 */
static void spi_pump_messages(struct kthread_work *work)
{
        struct spi_master *master =
                container_of(work, struct spi_master, pump_messages);

        __spi_pump_messages(master, true);
}

static int spi_init_queue(struct spi_master *master)
{
        struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };

        master->running = false;
        master->busy = false;

        init_kthread_worker(&master->kworker);
        master->kworker_task = kthread_run(kthread_worker_fn,
                                           &master->kworker, "%s",
                                           dev_name(&master->dev));
        if (IS_ERR(master->kworker_task)) {
                dev_err(&master->dev, "failed to create message pump task\n");
                return PTR_ERR(master->kworker_task);
        }
        init_kthread_work(&master->pump_messages, spi_pump_messages);

        /*
         * Master config will indicate if this controller should run the
         * message pump with high (realtime) priority to reduce the transfer
         * latency on the bus by minimising the delay between a transfer
         * request and the scheduling of the message pump thread. Without this
         * setting the message pump thread will remain at default priority.
         */
        if (master->rt) {
                dev_info(&master->dev,
                        "will run message pump with realtime priority\n");
                sched_setscheduler(master->kworker_task, SCHED_FIFO, &param);
        }

        return 0;
}

/**
 * spi_get_next_queued_message() - called by driver to check for queued
 * messages
 * @master: the master to check for queued messages
 *
 * If there are more messages in the queue, the next message is returned from
 * this call.
 *
 * Return: the next message in the queue, else NULL if the queue is empty.
 */
struct spi_message *spi_get_next_queued_message(struct spi_master *master)
{
        struct spi_message *next;
        unsigned long flags;

        /* get a pointer to the next message, if any */
        spin_lock_irqsave(&master->queue_lock, flags);
        next = list_first_entry_or_null(&master->queue, struct spi_message,
                                        queue);
        spin_unlock_irqrestore(&master->queue_lock, flags);

        return next;
}
EXPORT_SYMBOL_GPL(spi_get_next_queued_message);

/**
 * spi_finalize_current_message() - the current message is complete
 * @master: the master to return the message to
 *
 * Called by the driver to notify the core that the message in the front of the
 * queue is complete and can be removed from the queue.
 */
void spi_finalize_current_message(struct spi_master *master)
{
        struct spi_message *mesg;
        unsigned long flags;
        int ret;

        spin_lock_irqsave(&master->queue_lock, flags);
        mesg = master->cur_msg;
        spin_unlock_irqrestore(&master->queue_lock, flags);

        spi_unmap_msg(master, mesg);

        if (master->cur_msg_prepared && master->unprepare_message) {
                ret = master->unprepare_message(master, mesg);
                if (ret) {
                        dev_err(&master->dev,
                                "failed to unprepare message: %d\n", ret);
                }
        }

        spin_lock_irqsave(&master->queue_lock, flags);
        master->cur_msg = NULL;
        master->cur_msg_prepared = false;
        queue_kthread_work(&master->kworker, &master->pump_messages);
        spin_unlock_irqrestore(&master->queue_lock, flags);

        trace_spi_message_done(mesg);

        mesg->state = NULL;
        if (mesg->complete)
                mesg->complete(mesg->context);
}
EXPORT_SYMBOL_GPL(spi_finalize_current_message);

static int spi_start_queue(struct spi_master *master)
{
        unsigned long flags;

        spin_lock_irqsave(&master->queue_lock, flags);

        if (master->running || master->busy) {
                spin_unlock_irqrestore(&master->queue_lock, flags);
                return -EBUSY;
        }

        master->running = true;
        master->cur_msg = NULL;
        spin_unlock_irqrestore(&master->queue_lock, flags);

        queue_kthread_work(&master->kworker, &master->pump_messages);

        return 0;
}

static int spi_stop_queue(struct spi_master *master)
{
        unsigned long flags;
        unsigned limit = 500;
        int ret = 0;

        spin_lock_irqsave(&master->queue_lock, flags);

        /*
         * This is a bit lame, but is optimized for the common execution path.
         * A wait_queue on the master->busy could be used, but then the common
         * execution path (pump_messages) would be required to call wake_up or
         * friends on every SPI message. Do this instead.
         */
        while ((!list_empty(&master->queue) || master->busy) && limit--) {
                spin_unlock_irqrestore(&master->queue_lock, flags);
                usleep_range(10000, 11000);
                spin_lock_irqsave(&master->queue_lock, flags);
        }

        if (!list_empty(&master->queue) || master->busy)
                ret = -EBUSY;
        else
                master->running = false;

        spin_unlock_irqrestore(&master->queue_lock, flags);

        if (ret) {
                dev_warn(&master->dev,
                         "could not stop message queue\n");
                return ret;
        }
        return ret;
}

static int spi_destroy_queue(struct spi_master *master)
{
        int ret;

        ret = spi_stop_queue(master);

        /*
         * flush_kthread_worker will block until all work is done.
         * If the reason that stop_queue timed out is that the work will never
         * finish, then it does no good to call flush/stop thread, so
         * return anyway.
         */
        if (ret) {
                dev_err(&master->dev, "problem destroying queue\n");
                return ret;
        }

        flush_kthread_worker(&master->kworker);
        kthread_stop(master->kworker_task);

        return 0;
}

static int __spi_queued_transfer(struct spi_device *spi,
                                 struct spi_message *msg,
                                 bool need_pump)
{
        struct spi_master *master = spi->master;
        unsigned long flags;

        spin_lock_irqsave(&master->queue_lock, flags);

        if (!master->running) {
                spin_unlock_irqrestore(&master->queue_lock, flags);
                return -ESHUTDOWN;
        }
        msg->actual_length = 0;
        msg->status = -EINPROGRESS;

        list_add_tail(&msg->queue, &master->queue);
        if (!master->busy && need_pump)
                queue_kthread_work(&master->kworker, &master->pump_messages);

        spin_unlock_irqrestore(&master->queue_lock, flags);
        return 0;
}

/**
 * spi_queued_transfer - transfer function for queued transfers
 * @spi: spi device which is requesting transfer
 * @msg: spi message which is to handled is queued to driver queue
 *
 * Return: zero on success, else a negative error code.
 */
static int spi_queued_transfer(struct spi_device *spi, struct spi_message *msg)
{
        return __spi_queued_transfer(spi, msg, true);
}

static int spi_master_initialize_queue(struct spi_master *master)
{
        int ret;

        master->transfer = spi_queued_transfer;
        if (!master->transfer_one_message)
                master->transfer_one_message = spi_transfer_one_message;

        /* Initialize and start queue */
        ret = spi_init_queue(master);
        if (ret) {
                dev_err(&master->dev, "problem initializing queue\n");
                goto err_init_queue;
        }
        master->queued = true;
        ret = spi_start_queue(master);
        if (ret) {
                dev_err(&master->dev, "problem starting queue\n");
                goto err_start_queue;
        }

        return 0;

err_start_queue:
        spi_destroy_queue(master);
err_init_queue:
        return ret;
}

/*-------------------------------------------------------------------------*/

#if defined(CONFIG_OF)
static struct spi_device *
of_register_spi_device(struct spi_master *master, struct device_node *nc)
{
        struct spi_device *spi;
        int rc;
        u32 value;

        /* Alloc an spi_device */
        spi = spi_alloc_device(master);
        if (!spi) {
                dev_err(&master->dev, "spi_device alloc error for %s\n",
                        nc->full_name);
                rc = -ENOMEM;
                goto err_out;
        }

        /* Select device driver */
        rc = of_modalias_node(nc, spi->modalias,
                                sizeof(spi->modalias));
        if (rc < 0) {
                dev_err(&master->dev, "cannot find modalias for %s\n",
                        nc->full_name);
                goto err_out;
        }

        /* Device address */
        rc = of_property_read_u32(nc, "reg", &value);
        if (rc) {
                dev_err(&master->dev, "%s has no valid 'reg' property (%d)\n",
                        nc->full_name, rc);
                goto err_out;
        }
        spi->chip_select = value;

        /* Mode (clock phase/polarity/etc.) */
        if (of_find_property(nc, "spi-cpha", NULL))
                spi->mode |= SPI_CPHA;
        if (of_find_property(nc, "spi-cpol", NULL))
                spi->mode |= SPI_CPOL;
        if (of_find_property(nc, "spi-cs-high", NULL))
                spi->mode |= SPI_CS_HIGH;
        if (of_find_property(nc, "spi-3wire", NULL))
                spi->mode |= SPI_3WIRE;
        if (of_find_property(nc, "spi-lsb-first", NULL))
                spi->mode |= SPI_LSB_FIRST;

        /* Device DUAL/QUAD mode */
        if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
                switch (value) {
                case 1:
                        break;
                case 2:
                        spi->mode |= SPI_TX_DUAL;
                        break;
                case 4:
                        spi->mode |= SPI_TX_QUAD;
                        break;
                default:
                        dev_warn(&master->dev,
                                "spi-tx-bus-width %d not supported\n",
                                value);
                        break;
                }
        }

        if (!of_property_read_u32(nc, "spi-rx-bus-width", &value)) {
                switch (value) {
                case 1:
                        break;
                case 2:
                        spi->mode |= SPI_RX_DUAL;
                        break;
                case 4:
                        spi->mode |= SPI_RX_QUAD;
                        break;
                default:
                        dev_warn(&master->dev,
                                "spi-rx-bus-width %d not supported\n",
                                value);
                        break;
                }
        }

        /* Device speed */
        rc = of_property_read_u32(nc, "spi-max-frequency", &value);
        if (rc) {
                dev_err(&master->dev, "%s has no valid 'spi-max-frequency' property (%d)\n",
                        nc->full_name, rc);
                goto err_out;
        }
        spi->max_speed_hz = value;

        /* Store a pointer to the node in the device structure */
        of_node_get(nc);
        spi->dev.of_node = nc;

        /* Register the new device */
        rc = spi_add_device(spi);
        if (rc) {
                dev_err(&master->dev, "spi_device register error %s\n",
                        nc->full_name);
                goto err_out;
        }

        return spi;

err_out:
        spi_dev_put(spi);
        return ERR_PTR(rc);
}

/**
 * of_register_spi_devices() - Register child devices onto the SPI bus
 * @master:     Pointer to spi_master device
 *
 * Registers an spi_device for each child node of master node which has a 'reg'
 * property.
 */
static void of_register_spi_devices(struct spi_master *master)
{
        struct spi_device *spi;
        struct device_node *nc;

        if (!master->dev.of_node)
                return;

        for_each_available_child_of_node(master->dev.of_node, nc) {
                if (of_node_test_and_set_flag(nc, OF_POPULATED))
                        continue;
                spi = of_register_spi_device(master, nc);
                if (IS_ERR(spi))
                        dev_warn(&master->dev, "Failed to create SPI device for %s\n",
                                nc->full_name);
        }
}
#else
static void of_register_spi_devices(struct spi_master *master) { }
#endif

#ifdef CONFIG_ACPI
static int acpi_spi_add_resource(struct acpi_resource *ares, void *data)
{
        struct spi_device *spi = data;

        if (ares->type == ACPI_RESOURCE_TYPE_SERIAL_BUS) {
                struct acpi_resource_spi_serialbus *sb;

                sb = &ares->data.spi_serial_bus;
                if (sb->type == ACPI_RESOURCE_SERIAL_TYPE_SPI) {
                        spi->chip_select = sb->device_selection;
                        spi->max_speed_hz = sb->connection_speed;

                        if (sb->clock_phase == ACPI_SPI_SECOND_PHASE)
                                spi->mode |= SPI_CPHA;
                        if (sb->clock_polarity == ACPI_SPI_START_HIGH)
                                spi->mode |= SPI_CPOL;
                        if (sb->device_polarity == ACPI_SPI_ACTIVE_HIGH)
                                spi->mode |= SPI_CS_HIGH;
                }
        } else if (spi->irq < 0) {
                struct resource r;

                if (acpi_dev_resource_interrupt(ares, 0, &r))
                        spi->irq = r.start;
        }

        /* Always tell the ACPI core to skip this resource */
        return 1;
}

static acpi_status acpi_spi_add_device(acpi_handle handle, u32 level,
                                       void *data, void **return_value)
{
        struct spi_master *master = data;
        struct list_head resource_list;
        struct acpi_device *adev;
        struct spi_device *spi;
        int ret;

        if (acpi_bus_get_device(handle, &adev))
                return AE_OK;
        if (acpi_bus_get_status(adev) || !adev->status.present)
                return AE_OK;

        spi = spi_alloc_device(master);
        if (!spi) {
                dev_err(&master->dev, "failed to allocate SPI device for %s\n",
                        dev_name(&adev->dev));
                return AE_NO_MEMORY;
        }

        ACPI_COMPANION_SET(&spi->dev, adev);
        spi->irq = -1;

        INIT_LIST_HEAD(&resource_list);
        ret = acpi_dev_get_resources(adev, &resource_list,
                                     acpi_spi_add_resource, spi);
        acpi_dev_free_resource_list(&resource_list);

        if (ret < 0 || !spi->max_speed_hz) {
                spi_dev_put(spi);
                return AE_OK;
        }

        if (spi->irq < 0)
                spi->irq = acpi_dev_gpio_irq_get(adev, 0);

        adev->power.flags.ignore_parent = true;
        strlcpy(spi->modalias, acpi_device_hid(adev), sizeof(spi->modalias));
        if (spi_add_device(spi)) {
                adev->power.flags.ignore_parent = false;
                dev_err(&master->dev, "failed to add SPI device %s from ACPI\n",
                        dev_name(&adev->dev));
                spi_dev_put(spi);
        }

        return AE_OK;
}

static void acpi_register_spi_devices(struct spi_master *master)
{
        acpi_status status;
        acpi_handle handle;

        handle = ACPI_HANDLE(master->dev.parent);
        if (!handle)
                return;

        status = acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, 1,
                                     acpi_spi_add_device, NULL,
                                     master, NULL);
        if (ACPI_FAILURE(status))
                dev_warn(&master->dev, "failed to enumerate SPI slaves\n");
}
#else
static inline void acpi_register_spi_devices(struct spi_master *master) {}
#endif /* CONFIG_ACPI */

static void spi_master_release(struct device *dev)
{
        struct spi_master *master;

        master = container_of(dev, struct spi_master, dev);
        kfree(master);
}

static struct class spi_master_class = {
        .name           = "spi_master",
        .owner          = THIS_MODULE,
        .dev_release    = spi_master_release,
        .dev_groups     = spi_master_groups,
};


/**
 * spi_alloc_master - allocate SPI master controller
 * @dev: the controller, possibly using the platform_bus
 * @size: how much zeroed driver-private data to allocate; the pointer to this
 *      memory is in the driver_data field of the returned device,
 *      accessible with spi_master_get_devdata().
 * Context: can sleep
 *
 * This call is used only by SPI master controller drivers, which are the
 * only ones directly touching chip registers.  It's how they allocate
 * an spi_master structure, prior to calling spi_register_master().
 *
 * This must be called from context that can sleep.
 *
 * The caller is responsible for assigning the bus number and initializing
 * the master's methods before calling spi_register_master(); and (after errors
 * adding the device) calling spi_master_put() to prevent a memory leak.
 *
 * Return: the SPI master structure on success, else NULL.
 */
struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
{
        struct spi_master       *master;

        if (!dev)
                return NULL;

        master = kzalloc(size + sizeof(*master), GFP_KERNEL);
        if (!master)
                return NULL;

        device_initialize(&master->dev);
        master->bus_num = -1;
        master->num_chipselect = 1;
        master->dev.class = &spi_master_class;
        master->dev.parent = dev;
        spi_master_set_devdata(master, &master[1]);

        return master;
}
EXPORT_SYMBOL_GPL(spi_alloc_master);

#ifdef CONFIG_OF
static int of_spi_register_master(struct spi_master *master)
{
        int nb, i, *cs;
        struct device_node *np = master->dev.of_node;

        if (!np)
                return 0;

        nb = of_gpio_named_count(np, "cs-gpios");
        master->num_chipselect = max_t(int, nb, master->num_chipselect);

        /* Return error only for an incorrectly formed cs-gpios property */
        if (nb == 0 || nb == -ENOENT)
                return 0;
        else if (nb < 0)
                return nb;

        cs = devm_kzalloc(&master->dev,
                          sizeof(int) * master->num_chipselect,
                          GFP_KERNEL);
        master->cs_gpios = cs;

        if (!master->cs_gpios)
                return -ENOMEM;

        for (i = 0; i < master->num_chipselect; i++)
                cs[i] = -ENOENT;

        for (i = 0; i < nb; i++)
                cs[i] = of_get_named_gpio(np, "cs-gpios", i);

        return 0;
}
#else
static int of_spi_register_master(struct spi_master *master)
{
        return 0;
}
#endif

/**
 * spi_register_master - register SPI master controller
 * @master: initialized master, originally from spi_alloc_master()
 * Context: can sleep
 *
 * SPI master controllers connect to their drivers using some non-SPI bus,
 * such as the platform bus.  The final stage of probe() in that code
 * includes calling spi_register_master() to hook up to this SPI bus glue.
 *
 * SPI controllers use board specific (often SOC specific) bus numbers,
 * and board-specific addressing for SPI devices combines those numbers
 * with chip select numbers.  Since SPI does not directly support dynamic
 * device identification, boards need configuration tables telling which
 * chip is at which address.
 *
 * This must be called from context that can sleep.  It returns zero on
 * success, else a negative error code (dropping the master's refcount).
 * After a successful return, the caller is responsible for calling
 * spi_unregister_master().
 *
 * Return: zero on success, else a negative error code.
 */
int spi_register_master(struct spi_master *master)
{
        static atomic_t         dyn_bus_id = ATOMIC_INIT((1<<15) - 1);
        struct device           *dev = master->dev.parent;
        struct boardinfo        *bi;
        int                     status = -ENODEV;
        int                     dynamic = 0;

        if (!dev)
                return -ENODEV;

        status = of_spi_register_master(master);
        if (status)
                return status;

        /* even if it's just one always-selected device, there must
         * be at least one chipselect
         */
        if (master->num_chipselect == 0)
                return -EINVAL;

        if ((master->bus_num < 0) && master->dev.of_node)
                master->bus_num = of_alias_get_id(master->dev.of_node, "spi");

        /* convention:  dynamically assigned bus IDs count down from the max */
        if (master->bus_num < 0) {
                /* FIXME switch to an IDR based scheme, something like
                 * I2C now uses, so we can't run out of "dynamic" IDs
                 */
                master->bus_num = atomic_dec_return(&dyn_bus_id);
                dynamic = 1;
        }

        INIT_LIST_HEAD(&master->queue);
        spin_lock_init(&master->queue_lock);
        spin_lock_init(&master->bus_lock_spinlock);
        mutex_init(&master->bus_lock_mutex);
        master->bus_lock_flag = 0;
        init_completion(&master->xfer_completion);
        if (!master->max_dma_len)
                master->max_dma_len = INT_MAX;

        /* register the device, then userspace will see it.
         * registration fails if the bus ID is in use.
         */
        dev_set_name(&master->dev, "spi%u", master->bus_num);
        status = device_add(&master->dev);
        if (status < 0)
                goto done;
        dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev),
                        dynamic ? " (dynamic)" : "");

        /* If we're using a queued driver, start the queue */
        if (master->transfer)
                dev_info(dev, "master is unqueued, this is deprecated\n");
        else {
                status = spi_master_initialize_queue(master);
                if (status) {
                        device_del(&master->dev);
                        goto done;
                }
        }
        /* add statistics */
        spin_lock_init(&master->statistics.lock);

        mutex_lock(&board_lock);
        list_add_tail(&master->list, &spi_master_list);
        list_for_each_entry(bi, &board_list, list)
                spi_match_master_to_boardinfo(master, &bi->board_info);
        mutex_unlock(&board_lock);

        /* Register devices from the device tree and ACPI */
        of_register_spi_devices(master);
        acpi_register_spi_devices(master);
done:
        return status;
}
EXPORT_SYMBOL_GPL(spi_register_master);

static void devm_spi_unregister(struct device *dev, void *res)
{
        spi_unregister_master(*(struct spi_master **)res);
}

/**
 * dev_spi_register_master - register managed SPI master controller
 * @dev:    device managing SPI master
 * @master: initialized master, originally from spi_alloc_master()
 * Context: can sleep
 *
 * Register a SPI device as with spi_register_master() which will
 * automatically be unregister
 *
 * Return: zero on success, else a negative error code.
 */
int devm_spi_register_master(struct device *dev, struct spi_master *master)
{
        struct spi_master **ptr;
        int ret;

        ptr = devres_alloc(devm_spi_unregister, sizeof(*ptr), GFP_KERNEL);
        if (!ptr)
                return -ENOMEM;

        ret = spi_register_master(master);
        if (!ret) {
                *ptr = master;
                devres_add(dev, ptr);
        } else {
                devres_free(ptr);
        }

        return ret;
}
EXPORT_SYMBOL_GPL(devm_spi_register_master);

static int __unregister(struct device *dev, void *null)
{
        spi_unregister_device(to_spi_device(dev));
        return 0;
}

/**
 * spi_unregister_master - unregister SPI master controller
 * @master: the master being unregistered
 * Context: can sleep
 *
 * This call is used only by SPI master controller drivers, which are the
 * only ones directly touching chip registers.
 *
 * This must be called from context that can sleep.
 */
void spi_unregister_master(struct spi_master *master)
{
        int dummy;

        if (master->queued) {
                if (spi_destroy_queue(master))
                        dev_err(&master->dev, "queue remove failed\n");
        }

        mutex_lock(&board_lock);
        list_del(&master->list);
        mutex_unlock(&board_lock);

        dummy = device_for_each_child(&master->dev, NULL, __unregister);
        device_unregister(&master->dev);
}
EXPORT_SYMBOL_GPL(spi_unregister_master);

int spi_master_suspend(struct spi_master *master)
{
        int ret;

        /* Basically no-ops for non-queued masters */
        if (!master->queued)
                return 0;

        ret = spi_stop_queue(master);
        if (ret)
                dev_err(&master->dev, "queue stop failed\n");

        return ret;
}
EXPORT_SYMBOL_GPL(spi_master_suspend);

int spi_master_resume(struct spi_master *master)
{
        int ret;

        if (!master->queued)
                return 0;

        ret = spi_start_queue(master);
        if (ret)
                dev_err(&master->dev, "queue restart failed\n");

        return ret;
}
EXPORT_SYMBOL_GPL(spi_master_resume);

static int __spi_master_match(struct device *dev, const void *data)
{
        struct spi_master *m;
        const u16 *bus_num = data;

        m = container_of(dev, struct spi_master, dev);
        return m->bus_num == *bus_num;
}

/**
 * spi_busnum_to_master - look up master associated with bus_num
 * @bus_num: the master's bus number
 * Context: can sleep
 *
 * This call may be used with devices that are registered after
 * arch init time.  It returns a refcounted pointer to the relevant
 * spi_master (which the caller must release), or NULL if there is
 * no such master registered.
 *
 * Return: the SPI master structure on success, else NULL.
 */
struct spi_master *spi_busnum_to_master(u16 bus_num)
{
        struct device           *dev;
        struct spi_master       *master = NULL;

        dev = class_find_device(&spi_master_class, NULL, &bus_num,
                                __spi_master_match);
        if (dev)
                master = container_of(dev, struct spi_master, dev);
        /* reference got in class_find_device */
        return master;
}
EXPORT_SYMBOL_GPL(spi_busnum_to_master);

/*-------------------------------------------------------------------------*/

/* Core methods for SPI resource management */

/**
 * spi_res_alloc - allocate a spi resource that is life-cycle managed
 *                 during the processing of a spi_message while using
 *                 spi_transfer_one
 * @spi:     the spi device for which we allocate memory
 * @release: the release code to execute for this resource
 * @size:    size to alloc and return
 * @gfp:     GFP allocation flags
 *
 * Return: the pointer to the allocated data
 *
 * This may get enhanced in the future to allocate from a memory pool
 * of the @spi_device or @spi_master to avoid repeated allocations.
 */
void *spi_res_alloc(struct spi_device *spi,
                    spi_res_release_t release,
                    size_t size, gfp_t gfp)
{
        struct spi_res *sres;

        sres = kzalloc(sizeof(*sres) + size, gfp);
        if (!sres)
                return NULL;

        INIT_LIST_HEAD(&sres->entry);
        sres->release = release;

        return sres->data;
}
EXPORT_SYMBOL_GPL(spi_res_alloc);

/**
 * spi_res_free - free an spi resource
 * @res: pointer to the custom data of a resource
 *
 */
void spi_res_free(void *res)
{
        struct spi_res *sres = container_of(res, struct spi_res, data);

        if (!res)
                return;

        WARN_ON(!list_empty(&sres->entry));
        kfree(sres);
}
EXPORT_SYMBOL_GPL(spi_res_free);

/**
 * spi_res_add - add a spi_res to the spi_message
 * @message: the spi message
 * @res:     the spi_resource
 */
void spi_res_add(struct spi_message *message, void *res)
{
        struct spi_res *sres = container_of(res, struct spi_res, data);

        WARN_ON(!list_empty(&sres->entry));
        list_add_tail(&sres->entry, &message->resources);
}
EXPORT_SYMBOL_GPL(spi_res_add);

/**
 * spi_res_release - release all spi resources for this message
 * @master:  the @spi_master
 * @message: the @spi_message
 */
void spi_res_release(struct spi_master *master,
                     struct spi_message *message)
{
        struct spi_res *res;

        while (!list_empty(&message->resources)) {
                res = list_last_entry(&message->resources,
                                      struct spi_res, entry);

                if (res->release)
                        res->release(master, message, res->data);

                list_del(&res->entry);

                kfree(res);
        }
}
EXPORT_SYMBOL_GPL(spi_res_release);

/*-------------------------------------------------------------------------*/

/* Core methods for SPI master protocol drivers.  Some of the
 * other core methods are currently defined as inline functions.
 */

static int __spi_validate_bits_per_word(struct spi_master *master, u8 bits_per_word)
{
        if (master->bits_per_word_mask) {
                /* Only 32 bits fit in the mask */
                if (bits_per_word > 32)
                        return -EINVAL;
                if (!(master->bits_per_word_mask &
                                SPI_BPW_MASK(bits_per_word)))
                        return -EINVAL;
        }

        return 0;
}

/**
 * spi_setup - setup SPI mode and clock rate
 * @spi: the device whose settings are being modified
 * Context: can sleep, and no requests are queued to the device
 *
 * SPI protocol drivers may need to update the transfer mode if the
 * device doesn't work with its default.  They may likewise need
 * to update clock rates or word sizes from initial values.  This function
 * changes those settings, and must be called from a context that can sleep.
 * Except for SPI_CS_HIGH, which takes effect immediately, the changes take
 * effect the next time the device is selected and data is transferred to
 * or from it.  When this function returns, the spi device is deselected.
 *
 * Note that this call will fail if the protocol driver specifies an option
 * that the underlying controller or its driver does not support.  For
 * example, not all hardware supports wire transfers using nine bit words,
 * LSB-first wire encoding, or active-high chipselects.
 *
 * Return: zero on success, else a negative error code.
 */
int spi_setup(struct spi_device *spi)
{
        unsigned        bad_bits, ugly_bits;
        int             status;

        /* check mode to prevent that DUAL and QUAD set at the same time
         */
        if (((spi->mode & SPI_TX_DUAL) && (spi->mode & SPI_TX_QUAD)) ||
                ((spi->mode & SPI_RX_DUAL) && (spi->mode & SPI_RX_QUAD))) {
                dev_err(&spi->dev,
                "setup: can not select dual and quad at the same time\n");
                return -EINVAL;
        }
        /* if it is SPI_3WIRE mode, DUAL and QUAD should be forbidden
         */
        if ((spi->mode & SPI_3WIRE) && (spi->mode &
                (SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD)))
                return -EINVAL;
        /* help drivers fail *cleanly* when they need options
         * that aren't supported with their current master
         */
        bad_bits = spi->mode & ~spi->master->mode_bits;
        ugly_bits = bad_bits &
                    (SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD);
        if (ugly_bits) {
                dev_warn(&spi->dev,
                         "setup: ignoring unsupported mode bits %x\n",
                         ugly_bits);
                spi->mode &= ~ugly_bits;
                bad_bits &= ~ugly_bits;
        }
        if (bad_bits) {
                dev_err(&spi->dev, "setup: unsupported mode bits %x\n",
                        bad_bits);
                return -EINVAL;
        }

        if (!spi->bits_per_word)
                spi->bits_per_word = 8;

        status = __spi_validate_bits_per_word(spi->master, spi->bits_per_word);
        if (status)
                return status;

        if (!spi->max_speed_hz)
                spi->max_speed_hz = spi->master->max_speed_hz;

        if (spi->master->setup)
                status = spi->master->setup(spi);

        spi_set_cs(spi, false);

        dev_dbg(&spi->dev, "setup mode %d, %s%s%s%s%u bits/w, %u Hz max --> %d\n",
                        (int) (spi->mode & (SPI_CPOL | SPI_CPHA)),
                        (spi->mode & SPI_CS_HIGH) ? "cs_high, " : "",
                        (spi->mode & SPI_LSB_FIRST) ? "lsb, " : "",
                        (spi->mode & SPI_3WIRE) ? "3wire, " : "",
                        (spi->mode & SPI_LOOP) ? "loopback, " : "",
                        spi->bits_per_word, spi->max_speed_hz,
                        status);

        return status;
}
EXPORT_SYMBOL_GPL(spi_setup);

static int __spi_validate(struct spi_device *spi, struct spi_message *message)
{
        struct spi_master *master = spi->master;
        struct spi_transfer *xfer;
        int w_size;

        if (list_empty(&message->transfers))
                return -EINVAL;

        /* Half-duplex links include original MicroWire, and ones with
         * only one data pin like SPI_3WIRE (switches direction) or where
         * either MOSI or MISO is missing.  They can also be caused by
         * software limitations.
         */
        if ((master->flags & SPI_MASTER_HALF_DUPLEX)
                        || (spi->mode & SPI_3WIRE)) {
                unsigned flags = master->flags;

                list_for_each_entry(xfer, &message->transfers, transfer_list) {
                        if (xfer->rx_buf && xfer->tx_buf)
                                return -EINVAL;
                        if ((flags & SPI_MASTER_NO_TX) && xfer->tx_buf)
                                return -EINVAL;
                        if ((flags & SPI_MASTER_NO_RX) && xfer->rx_buf)
                                return -EINVAL;
                }
        }

        /**
         * Set transfer bits_per_word and max speed as spi device default if
         * it is not set for this transfer.
         * Set transfer tx_nbits and rx_nbits as single transfer default
         * (SPI_NBITS_SINGLE) if it is not set for this transfer.
         */
        message->frame_length = 0;
        list_for_each_entry(xfer, &message->transfers, transfer_list) {
                message->frame_length += xfer->len;
                if (!xfer->bits_per_word)
                        xfer->bits_per_word = spi->bits_per_word;

                if (!xfer->speed_hz)
                        xfer->speed_hz = spi->max_speed_hz;
                if (!xfer->speed_hz)
                        xfer->speed_hz = master->max_speed_hz;

                if (master->max_speed_hz &&
                    xfer->speed_hz > master->max_speed_hz)
                        xfer->speed_hz = master->max_speed_hz;

                if (__spi_validate_bits_per_word(master, xfer->bits_per_word))
                        return -EINVAL;

                /*
                 * SPI transfer length should be multiple of SPI word size
                 * where SPI word size should be power-of-two multiple
                 */
                if (xfer->bits_per_word <= 8)
                        w_size = 1;
                else if (xfer->bits_per_word <= 16)
                        w_size = 2;
                else
                        w_size = 4;

                /* No partial transfers accepted */
                if (xfer->len % w_size)
                        return -EINVAL;

                if (xfer->speed_hz && master->min_speed_hz &&
                    xfer->speed_hz < master->min_speed_hz)
                        return -EINVAL;

                if (xfer->tx_buf && !xfer->tx_nbits)
                        xfer->tx_nbits = SPI_NBITS_SINGLE;
                if (xfer->rx_buf && !xfer->rx_nbits)
                        xfer->rx_nbits = SPI_NBITS_SINGLE;
                /* check transfer tx/rx_nbits:
                 * 1. check the value matches one of single, dual and quad
                 * 2. check tx/rx_nbits match the mode in spi_device
                 */
                if (xfer->tx_buf) {
                        if (xfer->tx_nbits != SPI_NBITS_SINGLE &&
                                xfer->tx_nbits != SPI_NBITS_DUAL &&
                                xfer->tx_nbits != SPI_NBITS_QUAD)
                                return -EINVAL;
                        if ((xfer->tx_nbits == SPI_NBITS_DUAL) &&
                                !(spi->mode & (SPI_TX_DUAL | SPI_TX_QUAD)))
                                return -EINVAL;
                        if ((xfer->tx_nbits == SPI_NBITS_QUAD) &&
                                !(spi->mode & SPI_TX_QUAD))
                                return -EINVAL;
                }
                /* check transfer rx_nbits */
                if (xfer->rx_buf) {
                        if (xfer->rx_nbits != SPI_NBITS_SINGLE &&
                                xfer->rx_nbits != SPI_NBITS_DUAL &&
                                xfer->rx_nbits != SPI_NBITS_QUAD)
                                return -EINVAL;
                        if ((xfer->rx_nbits == SPI_NBITS_DUAL) &&
                                !(spi->mode & (SPI_RX_DUAL | SPI_RX_QUAD)))
                                return -EINVAL;
                        if ((xfer->rx_nbits == SPI_NBITS_QUAD) &&
                                !(spi->mode & SPI_RX_QUAD))
                                return -EINVAL;
                }
        }

        message->status = -EINPROGRESS;

        return 0;
}

static int __spi_async(struct spi_device *spi, struct spi_message *message)
{
        struct spi_master *master = spi->master;

        message->spi = spi;

        SPI_STATISTICS_INCREMENT_FIELD(&master->statistics, spi_async);
        SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics, spi_async);

        trace_spi_message_submit(message);

        return master->transfer(spi, message);
}

/**
 * spi_async - asynchronous SPI transfer
 * @spi: device with which data will be exchanged
 * @message: describes the data transfers, including completion callback
 * Context: any (irqs may be blocked, etc)
 *
 * This call may be used in_irq and other contexts which can't sleep,
 * as well as from task contexts which can sleep.
 *
 * The completion callback is invoked in a context which can't sleep.
 * Before that invocation, the value of message->status is undefined.
 * When the callback is issued, message->status holds either zero (to
 * indicate complete success) or a negative error code.  After that
 * callback returns, the driver which issued the transfer request may
 * deallocate the associated memory; it's no longer in use by any SPI
 * core or controller driver code.
 *
 * Note that although all messages to a spi_device are handled in
 * FIFO order, messages may go to different devices in other orders.
 * Some device might be higher priority, or have various "hard" access
 * time requirements, for example.
 *
 * On detection of any fault during the transfer, processing of
 * the entire message is aborted, and the device is deselected.
 * Until returning from the associated message completion callback,
 * no other spi_message queued to that device will be processed.
 * (This rule applies equally to all the synchronous transfer calls,
 * which are wrappers around this core asynchronous primitive.)
 *
 * Return: zero on success, else a negative error code.
 */
int spi_async(struct spi_device *spi, struct spi_message *message)
{
        struct spi_master *master = spi->master;
        int ret;
        unsigned long flags;

        ret = __spi_validate(spi, message);
        if (ret != 0)
                return ret;

        spin_lock_irqsave(&master->bus_lock_spinlock, flags);

        if (master->bus_lock_flag)
                ret = -EBUSY;
        else
                ret = __spi_async(spi, message);

        spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);

        return ret;
}
EXPORT_SYMBOL_GPL(spi_async);

/**
 * spi_async_locked - version of spi_async with exclusive bus usage
 * @spi: device with which data will be exchanged
 * @message: describes the data transfers, including completion callback
 * Context: any (irqs may be blocked, etc)
 *
 * This call may be used in_irq and other contexts which can't sleep,
 * as well as from task contexts which can sleep.
 *
 * The completion callback is invoked in a context which can't sleep.
 * Before that invocation, the value of message->status is undefined.
 * When the callback is issued, message->status holds either zero (to
 * indicate complete success) or a negative error code.  After that
 * callback returns, the driver which issued the transfer request may
 * deallocate the associated memory; it's no longer in use by any SPI
 * core or controller driver code.
 *
 * Note that although all messages to a spi_device are handled in
 * FIFO order, messages may go to different devices in other orders.
 * Some device might be higher priority, or have various "hard" access
 * time requirements, for example.
 *
 * On detection of any fault during the transfer, processing of
 * the entire message is aborted, and the device is deselected.
 * Until returning from the associated message completion callback,
 * no other spi_message queued to that device will be processed.
 * (This rule applies equally to all the synchronous transfer calls,
 * which are wrappers around this core asynchronous primitive.)
 *
 * Return: zero on success, else a negative error code.
 */
int spi_async_locked(struct spi_device *spi, struct spi_message *message)
{
        struct spi_master *master = spi->master;
        int ret;
        unsigned long flags;

        ret = __spi_validate(spi, message);
        if (ret != 0)
                return ret;

        spin_lock_irqsave(&master->bus_lock_spinlock, flags);

        ret = __spi_async(spi, message);

        spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);

        return ret;

}
EXPORT_SYMBOL_GPL(spi_async_locked);


/*-------------------------------------------------------------------------*/

/* Utility methods for SPI master protocol drivers, layered on
 * top of the core.  Some other utility methods are defined as
 * inline functions.
 */

static void spi_complete(void *arg)
{
        complete(arg);
}

static int __spi_sync(struct spi_device *spi, struct spi_message *message,
                      int bus_locked)
{
        DECLARE_COMPLETION_ONSTACK(done);
        int status;
        struct spi_master *master = spi->master;
        unsigned long flags;

        status = __spi_validate(spi, message);
        if (status != 0)
                return status;

        message->complete = spi_complete;
        message->context = &done;
        message->spi = spi;

        SPI_STATISTICS_INCREMENT_FIELD(&master->statistics, spi_sync);
        SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics, spi_sync);

        if (!bus_locked)
                mutex_lock(&master->bus_lock_mutex);

        /* If we're not using the legacy transfer method then we will
         * try to transfer in the calling context so special case.
         * This code would be less tricky if we could remove the
         * support for driver implemented message queues.
         */
        if (master->transfer == spi_queued_transfer) {
                spin_lock_irqsave(&master->bus_lock_spinlock, flags);

                trace_spi_message_submit(message);

                status = __spi_queued_transfer(spi, message, false);

                spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);
        } else {
                status = spi_async_locked(spi, message);
        }

        if (!bus_locked)
                mutex_unlock(&master->bus_lock_mutex);

        if (status == 0) {
                /* Push out the messages in the calling context if we
                 * can.
                 */
                if (master->transfer == spi_queued_transfer) {
                        SPI_STATISTICS_INCREMENT_FIELD(&master->statistics,
                                                       spi_sync_immediate);
                        SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics,
                                                       spi_sync_immediate);
                        __spi_pump_messages(master, false);
                }

                wait_for_completion(&done);
                status = message->status;
        }
        message->context = NULL;
        return status;
}

/**
 * spi_sync - blocking/synchronous SPI data transfers
 * @spi: device with which data will be exchanged
 * @message: describes the data transfers
 * Context: can sleep
 *
 * This call may only be used from a context that may sleep.  The sleep
 * is non-interruptible, and has no timeout.  Low-overhead controller
 * drivers may DMA directly into and out of the message buffers.
 *
 * Note that the SPI device's chip select is active during the message,
 * and then is normally disabled between messages.  Drivers for some
 * frequently-used devices may want to minimize costs of selecting a chip,
 * by leaving it selected in anticipation that the next message will go
 * to the same chip.  (That may increase power usage.)
 *
 * Also, the caller is guaranteeing that the memory associated with the
 * message will not be freed before this call returns.
 *
 * Return: zero on success, else a negative error code.
 */
int spi_sync(struct spi_device *spi, struct spi_message *message)
{
        return __spi_sync(spi, message, 0);
}
EXPORT_SYMBOL_GPL(spi_sync);

/**
 * spi_sync_locked - version of spi_sync with exclusive bus usage
 * @spi: device with which data will be exchanged
 * @message: describes the data transfers
 * Context: can sleep
 *
 * This call may only be used from a context that may sleep.  The sleep
 * is non-interruptible, and has no timeout.  Low-overhead controller
 * drivers may DMA directly into and out of the message buffers.
 *
 * This call should be used by drivers that require exclusive access to the
 * SPI bus. It has to be preceded by a spi_bus_lock call. The SPI bus must
 * be released by a spi_bus_unlock call when the exclusive access is over.
 *
 * Return: zero on success, else a negative error code.
 */
int spi_sync_locked(struct spi_device *spi, struct spi_message *message)
{
        return __spi_sync(spi, message, 1);
}
EXPORT_SYMBOL_GPL(spi_sync_locked);

/**
 * spi_bus_lock - obtain a lock for exclusive SPI bus usage
 * @master: SPI bus master that should be locked for exclusive bus access
 * Context: can sleep
 *
 * This call may only be used from a context that may sleep.  The sleep
 * is non-interruptible, and has no timeout.
 *
 * This call should be used by drivers that require exclusive access to the
 * SPI bus. The SPI bus must be released by a spi_bus_unlock call when the
 * exclusive access is over. Data transfer must be done by spi_sync_locked
 * and spi_async_locked calls when the SPI bus lock is held.
 *
 * Return: always zero.
 */
int spi_bus_lock(struct spi_master *master)
{
        unsigned long flags;

        mutex_lock(&master->bus_lock_mutex);

        spin_lock_irqsave(&master->bus_lock_spinlock, flags);
        master->bus_lock_flag = 1;
        spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);

        /* mutex remains locked until spi_bus_unlock is called */

        return 0;
}
EXPORT_SYMBOL_GPL(spi_bus_lock);

/**
 * spi_bus_unlock - release the lock for exclusive SPI bus usage
 * @master: SPI bus master that was locked for exclusive bus access
 * Context: can sleep
 *
 * This call may only be used from a context that may sleep.  The sleep
 * is non-interruptible, and has no timeout.
 *
 * This call releases an SPI bus lock previously obtained by an spi_bus_lock
 * call.
 *
 * Return: always zero.
 */
int spi_bus_unlock(struct spi_master *master)
{
        master->bus_lock_flag = 0;

        mutex_unlock(&master->bus_lock_mutex);

        return 0;
}
EXPORT_SYMBOL_GPL(spi_bus_unlock);

/* portable code must never pass more than 32 bytes */
#define SPI_BUFSIZ      max(32, SMP_CACHE_BYTES)

static u8       *buf;

/**
 * spi_write_then_read - SPI synchronous write followed by read
 * @spi: device with which data will be exchanged
 * @txbuf: data to be written (need not be dma-safe)
 * @n_tx: size of txbuf, in bytes
 * @rxbuf: buffer into which data will be read (need not be dma-safe)
 * @n_rx: size of rxbuf, in bytes
 * Context: can sleep
 *
 * This performs a half duplex MicroWire style transaction with the
 * device, sending txbuf and then reading rxbuf.  The return value
 * is zero for success, else a negative errno status code.
 * This call may only be used from a context that may sleep.
 *
 * Parameters to this routine are always copied using a small buffer;
 * portable code should never use this for more than 32 bytes.
 * Performance-sensitive or bulk transfer code should instead use
 * spi_{async,sync}() calls with dma-safe buffers.
 *
 * Return: zero on success, else a negative error code.
 */
int spi_write_then_read(struct spi_device *spi,
                const void *txbuf, unsigned n_tx,
                void *rxbuf, unsigned n_rx)
{
        static DEFINE_MUTEX(lock);

        int                     status;
        struct spi_message      message;
        struct spi_transfer     x[2];
        u8                      *local_buf;

        /* Use preallocated DMA-safe buffer if we can.  We can't avoid
         * copying here, (as a pure convenience thing), but we can
         * keep heap costs out of the hot path unless someone else is
         * using the pre-allocated buffer or the transfer is too large.
         */
        if ((n_tx + n_rx) > SPI_BUFSIZ || !mutex_trylock(&lock)) {
                local_buf = kmalloc(max((unsigned)SPI_BUFSIZ, n_tx + n_rx),
                                    GFP_KERNEL | GFP_DMA);
                if (!local_buf)
                        return -ENOMEM;
        } else {
                local_buf = buf;
        }

        spi_message_init(&message);
        memset(x, 0, sizeof(x));
        if (n_tx) {
                x[0].len = n_tx;
                spi_message_add_tail(&x[0], &message);
        }
        if (n_rx) {
                x[1].len = n_rx;
                spi_message_add_tail(&x[1], &message);
        }

        memcpy(local_buf, txbuf, n_tx);
        x[0].tx_buf = local_buf;
        x[1].rx_buf = local_buf + n_tx;

        /* do the i/o */
        status = spi_sync(spi, &message);
        if (status == 0)
                memcpy(rxbuf, x[1].rx_buf, n_rx);

        if (x[0].tx_buf == buf)
                mutex_unlock(&lock);
        else
                kfree(local_buf);

        return status;
}
EXPORT_SYMBOL_GPL(spi_write_then_read);

/*-------------------------------------------------------------------------*/

#if IS_ENABLED(CONFIG_OF_DYNAMIC)
static int __spi_of_device_match(struct device *dev, void *data)
{
        return dev->of_node == data;
}

/* must call put_device() when done with returned spi_device device */
static struct spi_device *of_find_spi_device_by_node(struct device_node *node)
{
        struct device *dev = bus_find_device(&spi_bus_type, NULL, node,
                                                __spi_of_device_match);
        return dev ? to_spi_device(dev) : NULL;
}

static int __spi_of_master_match(struct device *dev, const void *data)
{
        return dev->of_node == data;
}

/* the spi masters are not using spi_bus, so we find it with another way */
static struct spi_master *of_find_spi_master_by_node(struct device_node *node)
{
        struct device *dev;

        dev = class_find_device(&spi_master_class, NULL, node,
                                __spi_of_master_match);
        if (!dev)
                return NULL;

        /* reference got in class_find_device */
        return container_of(dev, struct spi_master, dev);
}

static int of_spi_notify(struct notifier_block *nb, unsigned long action,
                         void *arg)
{
        struct of_reconfig_data *rd = arg;
        struct spi_master *master;
        struct spi_device *spi;

        switch (of_reconfig_get_state_change(action, arg)) {
        case OF_RECONFIG_CHANGE_ADD:
                master = of_find_spi_master_by_node(rd->dn->parent);
                if (master == NULL)
                        return NOTIFY_OK;       /* not for us */

                if (of_node_test_and_set_flag(rd->dn, OF_POPULATED)) {
                        put_device(&master->dev);
                        return NOTIFY_OK;
                }

                spi = of_register_spi_device(master, rd->dn);
                put_device(&master->dev);

                if (IS_ERR(spi)) {
                        pr_err("%s: failed to create for '%s'\n",
                                        __func__, rd->dn->full_name);
                        return notifier_from_errno(PTR_ERR(spi));
                }
                break;

        case OF_RECONFIG_CHANGE_REMOVE:
                /* already depopulated? */
                if (!of_node_check_flag(rd->dn, OF_POPULATED))
                        return NOTIFY_OK;

                /* find our device by node */
                spi = of_find_spi_device_by_node(rd->dn);
                if (spi == NULL)
                        return NOTIFY_OK;       /* no? not meant for us */

                /* unregister takes one ref away */
                spi_unregister_device(spi);

                /* and put the reference of the find */
                put_device(&spi->dev);
                break;
        }

        return NOTIFY_OK;
}

static struct notifier_block spi_of_notifier = {
        .notifier_call = of_spi_notify,
};
#else /* IS_ENABLED(CONFIG_OF_DYNAMIC) */
extern struct notifier_block spi_of_notifier;
#endif /* IS_ENABLED(CONFIG_OF_DYNAMIC) */

static int __init spi_init(void)
{
        int     status;

        buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
        if (!buf) {
                status = -ENOMEM;
                goto err0;
        }

        status = bus_register(&spi_bus_type);
        if (status < 0)
                goto err1;

        status = class_register(&spi_master_class);
        if (status < 0)
                goto err2;

        if (IS_ENABLED(CONFIG_OF_DYNAMIC))
                WARN_ON(of_reconfig_notifier_register(&spi_of_notifier));

        return 0;

err2:
        bus_unregister(&spi_bus_type);
err1:
        kfree(buf);
        buf = NULL;
err0:
        return status;
}

/* board_info is normally registered in arch_initcall(),
 * but even essential drivers wait till later
 *
 * REVISIT only boardinfo really needs static linking. the rest (device and
 * driver registration) _could_ be dynamically linked (modular) ... costs
 * include needing to have boardinfo data structures be much more public.
 */
postcore_initcall(spi_init);