Merge tag 'v4.20' into for-linus

[mirror_ubuntu-jammy-kernel.git] / drivers / firmware / qemu_fw_cfg.c

/*
 * drivers/firmware/qemu_fw_cfg.c
 *
 * Copyright 2015 Carnegie Mellon University
 *
 * Expose entries from QEMU's firmware configuration (fw_cfg) device in
 * sysfs (read-only, under "/sys/firmware/qemu_fw_cfg/...").
 *
 * The fw_cfg device may be instantiated via either an ACPI node (on x86
 * and select subsets of aarch64), a Device Tree node (on arm), or using
 * a kernel module (or command line) parameter with the following syntax:
 *
 *      [qemu_fw_cfg.]ioport=<size>@<base>[:<ctrl_off>:<data_off>[:<dma_off>]]
 * or
 *      [qemu_fw_cfg.]mmio=<size>@<base>[:<ctrl_off>:<data_off>[:<dma_off>]]
 *
 * where:
 *      <size>     := size of ioport or mmio range
 *      <base>     := physical base address of ioport or mmio range
 *      <ctrl_off> := (optional) offset of control register
 *      <data_off> := (optional) offset of data register
 *      <dma_off> := (optional) offset of dma register
 *
 * e.g.:
 *      qemu_fw_cfg.ioport=12@0x510:0:1:4       (the default on x86)
 * or
 *      qemu_fw_cfg.mmio=16@0x9020000:8:0:16    (the default on arm)
 */

#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/platform_device.h>
#include <linux/acpi.h>
#include <linux/slab.h>
#include <linux/io.h>
#include <linux/ioport.h>
#include <uapi/linux/qemu_fw_cfg.h>
#include <linux/delay.h>
#include <linux/crash_dump.h>
#include <linux/crash_core.h>

MODULE_AUTHOR("Gabriel L. Somlo <somlo@cmu.edu>");
MODULE_DESCRIPTION("QEMU fw_cfg sysfs support");
MODULE_LICENSE("GPL");

/* fw_cfg revision attribute, in /sys/firmware/qemu_fw_cfg top-level dir. */
static u32 fw_cfg_rev;

/* fw_cfg device i/o register addresses */
static bool fw_cfg_is_mmio;
static phys_addr_t fw_cfg_p_base;
static resource_size_t fw_cfg_p_size;
static void __iomem *fw_cfg_dev_base;
static void __iomem *fw_cfg_reg_ctrl;
static void __iomem *fw_cfg_reg_data;
static void __iomem *fw_cfg_reg_dma;

/* atomic access to fw_cfg device (potentially slow i/o, so using mutex) */
static DEFINE_MUTEX(fw_cfg_dev_lock);

/* pick appropriate endianness for selector key */
static void fw_cfg_sel_endianness(u16 key)
{
        if (fw_cfg_is_mmio)
                iowrite16be(key, fw_cfg_reg_ctrl);
        else
                iowrite16(key, fw_cfg_reg_ctrl);
}

#ifdef CONFIG_CRASH_CORE
static inline bool fw_cfg_dma_enabled(void)
{
        return (fw_cfg_rev & FW_CFG_VERSION_DMA) && fw_cfg_reg_dma;
}

/* qemu fw_cfg device is sync today, but spec says it may become async */
static void fw_cfg_wait_for_control(struct fw_cfg_dma_access *d)
{
        for (;;) {
                u32 ctrl = be32_to_cpu(READ_ONCE(d->control));

                /* do not reorder the read to d->control */
                rmb();
                if ((ctrl & ~FW_CFG_DMA_CTL_ERROR) == 0)
                        return;

                cpu_relax();
        }
}

static ssize_t fw_cfg_dma_transfer(void *address, u32 length, u32 control)
{
        phys_addr_t dma;
        struct fw_cfg_dma_access *d = NULL;
        ssize_t ret = length;

        d = kmalloc(sizeof(*d), GFP_KERNEL);
        if (!d) {
                ret = -ENOMEM;
                goto end;
        }

        /* fw_cfg device does not need IOMMU protection, so use physical addresses */
        *d = (struct fw_cfg_dma_access) {
                .address = cpu_to_be64(address ? virt_to_phys(address) : 0),
                .length = cpu_to_be32(length),
                .control = cpu_to_be32(control)
        };

        dma = virt_to_phys(d);

        iowrite32be((u64)dma >> 32, fw_cfg_reg_dma);
        /* force memory to sync before notifying device via MMIO */
        wmb();
        iowrite32be(dma, fw_cfg_reg_dma + 4);

        fw_cfg_wait_for_control(d);

        if (be32_to_cpu(READ_ONCE(d->control)) & FW_CFG_DMA_CTL_ERROR) {
                ret = -EIO;
        }

end:
        kfree(d);

        return ret;
}
#endif

/* read chunk of given fw_cfg blob (caller responsible for sanity-check) */
static ssize_t fw_cfg_read_blob(u16 key,
                                void *buf, loff_t pos, size_t count)
{
        u32 glk = -1U;
        acpi_status status;

        /* If we have ACPI, ensure mutual exclusion against any potential
         * device access by the firmware, e.g. via AML methods:
         */
        status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk);
        if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) {
                /* Should never get here */
                WARN(1, "fw_cfg_read_blob: Failed to lock ACPI!\n");
                memset(buf, 0, count);
                return -EINVAL;
        }

        mutex_lock(&fw_cfg_dev_lock);
        fw_cfg_sel_endianness(key);
        while (pos-- > 0)
                ioread8(fw_cfg_reg_data);
        ioread8_rep(fw_cfg_reg_data, buf, count);
        mutex_unlock(&fw_cfg_dev_lock);

        acpi_release_global_lock(glk);
        return count;
}

#ifdef CONFIG_CRASH_CORE
/* write chunk of given fw_cfg blob (caller responsible for sanity-check) */
static ssize_t fw_cfg_write_blob(u16 key,
                                 void *buf, loff_t pos, size_t count)
{
        u32 glk = -1U;
        acpi_status status;
        ssize_t ret = count;

        /* If we have ACPI, ensure mutual exclusion against any potential
         * device access by the firmware, e.g. via AML methods:
         */
        status = acpi_acquire_global_lock(ACPI_WAIT_FOREVER, &glk);
        if (ACPI_FAILURE(status) && status != AE_NOT_CONFIGURED) {
                /* Should never get here */
                WARN(1, "%s: Failed to lock ACPI!\n", __func__);
                return -EINVAL;
        }

        mutex_lock(&fw_cfg_dev_lock);
        if (pos == 0) {
                ret = fw_cfg_dma_transfer(buf, count, key << 16
                                          | FW_CFG_DMA_CTL_SELECT
                                          | FW_CFG_DMA_CTL_WRITE);
        } else {
                fw_cfg_sel_endianness(key);
                ret = fw_cfg_dma_transfer(NULL, pos, FW_CFG_DMA_CTL_SKIP);
                if (ret < 0)
                        goto end;
                ret = fw_cfg_dma_transfer(buf, count, FW_CFG_DMA_CTL_WRITE);
        }

end:
        mutex_unlock(&fw_cfg_dev_lock);

        acpi_release_global_lock(glk);

        return ret;
}
#endif /* CONFIG_CRASH_CORE */

/* clean up fw_cfg device i/o */
static void fw_cfg_io_cleanup(void)
{
        if (fw_cfg_is_mmio) {
                iounmap(fw_cfg_dev_base);
                release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
        } else {
                ioport_unmap(fw_cfg_dev_base);
                release_region(fw_cfg_p_base, fw_cfg_p_size);
        }
}

/* arch-specific ctrl & data register offsets are not available in ACPI, DT */
#if !(defined(FW_CFG_CTRL_OFF) && defined(FW_CFG_DATA_OFF))
# if (defined(CONFIG_ARM) || defined(CONFIG_ARM64))
#  define FW_CFG_CTRL_OFF 0x08
#  define FW_CFG_DATA_OFF 0x00
#  define FW_CFG_DMA_OFF 0x10
# elif (defined(CONFIG_PPC_PMAC) || defined(CONFIG_SPARC32)) /* ppc/mac,sun4m */
#  define FW_CFG_CTRL_OFF 0x00
#  define FW_CFG_DATA_OFF 0x02
# elif (defined(CONFIG_X86) || defined(CONFIG_SPARC64)) /* x86, sun4u */
#  define FW_CFG_CTRL_OFF 0x00
#  define FW_CFG_DATA_OFF 0x01
#  define FW_CFG_DMA_OFF 0x04
# else
#  error "QEMU FW_CFG not available on this architecture!"
# endif
#endif

/* initialize fw_cfg device i/o from platform data */
static int fw_cfg_do_platform_probe(struct platform_device *pdev)
{
        char sig[FW_CFG_SIG_SIZE];
        struct resource *range, *ctrl, *data, *dma;

        /* acquire i/o range details */
        fw_cfg_is_mmio = false;
        range = platform_get_resource(pdev, IORESOURCE_IO, 0);
        if (!range) {
                fw_cfg_is_mmio = true;
                range = platform_get_resource(pdev, IORESOURCE_MEM, 0);
                if (!range)
                        return -EINVAL;
        }
        fw_cfg_p_base = range->start;
        fw_cfg_p_size = resource_size(range);

        if (fw_cfg_is_mmio) {
                if (!request_mem_region(fw_cfg_p_base,
                                        fw_cfg_p_size, "fw_cfg_mem"))
                        return -EBUSY;
                fw_cfg_dev_base = ioremap(fw_cfg_p_base, fw_cfg_p_size);
                if (!fw_cfg_dev_base) {
                        release_mem_region(fw_cfg_p_base, fw_cfg_p_size);
                        return -EFAULT;
                }
        } else {
                if (!request_region(fw_cfg_p_base,
                                    fw_cfg_p_size, "fw_cfg_io"))
                        return -EBUSY;
                fw_cfg_dev_base = ioport_map(fw_cfg_p_base, fw_cfg_p_size);
                if (!fw_cfg_dev_base) {
                        release_region(fw_cfg_p_base, fw_cfg_p_size);
                        return -EFAULT;
                }
        }

        /* were custom register offsets provided (e.g. on the command line)? */
        ctrl = platform_get_resource_byname(pdev, IORESOURCE_REG, "ctrl");
        data = platform_get_resource_byname(pdev, IORESOURCE_REG, "data");
        dma = platform_get_resource_byname(pdev, IORESOURCE_REG, "dma");
        if (ctrl && data) {
                fw_cfg_reg_ctrl = fw_cfg_dev_base + ctrl->start;
                fw_cfg_reg_data = fw_cfg_dev_base + data->start;
        } else {
                /* use architecture-specific offsets */
                fw_cfg_reg_ctrl = fw_cfg_dev_base + FW_CFG_CTRL_OFF;
                fw_cfg_reg_data = fw_cfg_dev_base + FW_CFG_DATA_OFF;
        }

        if (dma)
                fw_cfg_reg_dma = fw_cfg_dev_base + dma->start;
#ifdef FW_CFG_DMA_OFF
        else
                fw_cfg_reg_dma = fw_cfg_dev_base + FW_CFG_DMA_OFF;
#endif

        /* verify fw_cfg device signature */
        if (fw_cfg_read_blob(FW_CFG_SIGNATURE, sig,
                                0, FW_CFG_SIG_SIZE) < 0 ||
                memcmp(sig, "QEMU", FW_CFG_SIG_SIZE) != 0) {
                fw_cfg_io_cleanup();
                return -ENODEV;
        }

        return 0;
}

static ssize_t fw_cfg_showrev(struct kobject *k, struct attribute *a, char *buf)
{
        return sprintf(buf, "%u\n", fw_cfg_rev);
}

static const struct {
        struct attribute attr;
        ssize_t (*show)(struct kobject *k, struct attribute *a, char *buf);
} fw_cfg_rev_attr = {
        .attr = { .name = "rev", .mode = S_IRUSR },
        .show = fw_cfg_showrev,
};

/* fw_cfg_sysfs_entry type */
struct fw_cfg_sysfs_entry {
        struct kobject kobj;
        u32 size;
        u16 select;
        char name[FW_CFG_MAX_FILE_PATH];
        struct list_head list;
};

#ifdef CONFIG_CRASH_CORE
static ssize_t fw_cfg_write_vmcoreinfo(const struct fw_cfg_file *f)
{
        static struct fw_cfg_vmcoreinfo *data;
        ssize_t ret;

        data = kmalloc(sizeof(struct fw_cfg_vmcoreinfo), GFP_KERNEL);
        if (!data)
                return -ENOMEM;

        *data = (struct fw_cfg_vmcoreinfo) {
                .guest_format = cpu_to_le16(FW_CFG_VMCOREINFO_FORMAT_ELF),
                .size = cpu_to_le32(VMCOREINFO_NOTE_SIZE),
                .paddr = cpu_to_le64(paddr_vmcoreinfo_note())
        };
        /* spare ourself reading host format support for now since we
         * don't know what else to format - host may ignore ours
         */
        ret = fw_cfg_write_blob(be16_to_cpu(f->select), data,
                                0, sizeof(struct fw_cfg_vmcoreinfo));

        kfree(data);
        return ret;
}
#endif /* CONFIG_CRASH_CORE */

/* get fw_cfg_sysfs_entry from kobject member */
static inline struct fw_cfg_sysfs_entry *to_entry(struct kobject *kobj)
{
        return container_of(kobj, struct fw_cfg_sysfs_entry, kobj);
}

/* fw_cfg_sysfs_attribute type */
struct fw_cfg_sysfs_attribute {
        struct attribute attr;
        ssize_t (*show)(struct fw_cfg_sysfs_entry *entry, char *buf);
};

/* get fw_cfg_sysfs_attribute from attribute member */
static inline struct fw_cfg_sysfs_attribute *to_attr(struct attribute *attr)
{
        return container_of(attr, struct fw_cfg_sysfs_attribute, attr);
}

/* global cache of fw_cfg_sysfs_entry objects */
static LIST_HEAD(fw_cfg_entry_cache);

/* kobjects removed lazily by kernel, mutual exclusion needed */
static DEFINE_SPINLOCK(fw_cfg_cache_lock);

static inline void fw_cfg_sysfs_cache_enlist(struct fw_cfg_sysfs_entry *entry)
{
        spin_lock(&fw_cfg_cache_lock);
        list_add_tail(&entry->list, &fw_cfg_entry_cache);
        spin_unlock(&fw_cfg_cache_lock);
}

static inline void fw_cfg_sysfs_cache_delist(struct fw_cfg_sysfs_entry *entry)
{
        spin_lock(&fw_cfg_cache_lock);
        list_del(&entry->list);
        spin_unlock(&fw_cfg_cache_lock);
}

static void fw_cfg_sysfs_cache_cleanup(void)
{
        struct fw_cfg_sysfs_entry *entry, *next;

        list_for_each_entry_safe(entry, next, &fw_cfg_entry_cache, list) {
                /* will end up invoking fw_cfg_sysfs_cache_delist()
                 * via each object's release() method (i.e. destructor)
                 */
                kobject_put(&entry->kobj);
        }
}

/* default_attrs: per-entry attributes and show methods */

#define FW_CFG_SYSFS_ATTR(_attr) \
struct fw_cfg_sysfs_attribute fw_cfg_sysfs_attr_##_attr = { \
        .attr = { .name = __stringify(_attr), .mode = S_IRUSR }, \
        .show = fw_cfg_sysfs_show_##_attr, \
}

static ssize_t fw_cfg_sysfs_show_size(struct fw_cfg_sysfs_entry *e, char *buf)
{
        return sprintf(buf, "%u\n", e->size);
}

static ssize_t fw_cfg_sysfs_show_key(struct fw_cfg_sysfs_entry *e, char *buf)
{
        return sprintf(buf, "%u\n", e->select);
}

static ssize_t fw_cfg_sysfs_show_name(struct fw_cfg_sysfs_entry *e, char *buf)
{
        return sprintf(buf, "%s\n", e->name);
}

static FW_CFG_SYSFS_ATTR(size);
static FW_CFG_SYSFS_ATTR(key);
static FW_CFG_SYSFS_ATTR(name);

static struct attribute *fw_cfg_sysfs_entry_attrs[] = {
        &fw_cfg_sysfs_attr_size.attr,
        &fw_cfg_sysfs_attr_key.attr,
        &fw_cfg_sysfs_attr_name.attr,
        NULL,
};

/* sysfs_ops: find fw_cfg_[entry, attribute] and call appropriate show method */
static ssize_t fw_cfg_sysfs_attr_show(struct kobject *kobj, struct attribute *a,
                                      char *buf)
{
        struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
        struct fw_cfg_sysfs_attribute *attr = to_attr(a);

        return attr->show(entry, buf);
}

static const struct sysfs_ops fw_cfg_sysfs_attr_ops = {
        .show = fw_cfg_sysfs_attr_show,
};

/* release: destructor, to be called via kobject_put() */
static void fw_cfg_sysfs_release_entry(struct kobject *kobj)
{
        struct fw_cfg_sysfs_entry *entry = to_entry(kobj);

        fw_cfg_sysfs_cache_delist(entry);
        kfree(entry);
}

/* kobj_type: ties together all properties required to register an entry */
static struct kobj_type fw_cfg_sysfs_entry_ktype = {
        .default_attrs = fw_cfg_sysfs_entry_attrs,
        .sysfs_ops = &fw_cfg_sysfs_attr_ops,
        .release = fw_cfg_sysfs_release_entry,
};

/* raw-read method and attribute */
static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
                                     struct bin_attribute *bin_attr,
                                     char *buf, loff_t pos, size_t count)
{
        struct fw_cfg_sysfs_entry *entry = to_entry(kobj);

        if (pos > entry->size)
                return -EINVAL;

        if (count > entry->size - pos)
                count = entry->size - pos;

        return fw_cfg_read_blob(entry->select, buf, pos, count);
}

static struct bin_attribute fw_cfg_sysfs_attr_raw = {
        .attr = { .name = "raw", .mode = S_IRUSR },
        .read = fw_cfg_sysfs_read_raw,
};

/*
 * Create a kset subdirectory matching each '/' delimited dirname token
 * in 'name', starting with sysfs kset/folder 'dir'; At the end, create
 * a symlink directed at the given 'target'.
 * NOTE: We do this on a best-effort basis, since 'name' is not guaranteed
 * to be a well-behaved path name. Whenever a symlink vs. kset directory
 * name collision occurs, the kernel will issue big scary warnings while
 * refusing to add the offending link or directory. We follow up with our
 * own, slightly less scary error messages explaining the situation :)
 */
static int fw_cfg_build_symlink(struct kset *dir,
                                struct kobject *target, const char *name)
{
        int ret;
        struct kset *subdir;
        struct kobject *ko;
        char *name_copy, *p, *tok;

        if (!dir || !target || !name || !*name)
                return -EINVAL;

        /* clone a copy of name for parsing */
        name_copy = p = kstrdup(name, GFP_KERNEL);
        if (!name_copy)
                return -ENOMEM;

        /* create folders for each dirname token, then symlink for basename */
        while ((tok = strsep(&p, "/")) && *tok) {

                /* last (basename) token? If so, add symlink here */
                if (!p || !*p) {
                        ret = sysfs_create_link(&dir->kobj, target, tok);
                        break;
                }

                /* does the current dir contain an item named after tok ? */
                ko = kset_find_obj(dir, tok);
                if (ko) {
                        /* drop reference added by kset_find_obj */
                        kobject_put(ko);

                        /* ko MUST be a kset - we're about to use it as one ! */
                        if (ko->ktype != dir->kobj.ktype) {
                                ret = -EINVAL;
                                break;
                        }

                        /* descend into already existing subdirectory */
                        dir = to_kset(ko);
                } else {
                        /* create new subdirectory kset */
                        subdir = kzalloc(sizeof(struct kset), GFP_KERNEL);
                        if (!subdir) {
                                ret = -ENOMEM;
                                break;
                        }
                        subdir->kobj.kset = dir;
                        subdir->kobj.ktype = dir->kobj.ktype;
                        ret = kobject_set_name(&subdir->kobj, "%s", tok);
                        if (ret) {
                                kfree(subdir);
                                break;
                        }
                        ret = kset_register(subdir);
                        if (ret) {
                                kfree(subdir);
                                break;
                        }

                        /* descend into newly created subdirectory */
                        dir = subdir;
                }
        }

        /* we're done with cloned copy of name */
        kfree(name_copy);
        return ret;
}

/* recursively unregister fw_cfg/by_name/ kset directory tree */
static void fw_cfg_kset_unregister_recursive(struct kset *kset)
{
        struct kobject *k, *next;

        list_for_each_entry_safe(k, next, &kset->list, entry)
                /* all set members are ksets too, but check just in case... */
                if (k->ktype == kset->kobj.ktype)
                        fw_cfg_kset_unregister_recursive(to_kset(k));

        /* symlinks are cleanly and automatically removed with the directory */
        kset_unregister(kset);
}

/* kobjects & kset representing top-level, by_key, and by_name folders */
static struct kobject *fw_cfg_top_ko;
static struct kobject *fw_cfg_sel_ko;
static struct kset *fw_cfg_fname_kset;

/* register an individual fw_cfg file */
static int fw_cfg_register_file(const struct fw_cfg_file *f)
{
        int err;
        struct fw_cfg_sysfs_entry *entry;

#ifdef CONFIG_CRASH_CORE
        if (fw_cfg_dma_enabled() &&
                strcmp(f->name, FW_CFG_VMCOREINFO_FILENAME) == 0 &&
                !is_kdump_kernel()) {
                if (fw_cfg_write_vmcoreinfo(f) < 0)
                        pr_warn("fw_cfg: failed to write vmcoreinfo");
        }
#endif

        /* allocate new entry */
        entry = kzalloc(sizeof(*entry), GFP_KERNEL);
        if (!entry)
                return -ENOMEM;

        /* set file entry information */
        entry->size = be32_to_cpu(f->size);
        entry->select = be16_to_cpu(f->select);
        memcpy(entry->name, f->name, FW_CFG_MAX_FILE_PATH);

        /* register entry under "/sys/firmware/qemu_fw_cfg/by_key/" */
        err = kobject_init_and_add(&entry->kobj, &fw_cfg_sysfs_entry_ktype,
                                   fw_cfg_sel_ko, "%d", entry->select);
        if (err)
                goto err_register;

        /* add raw binary content access */
        err = sysfs_create_bin_file(&entry->kobj, &fw_cfg_sysfs_attr_raw);
        if (err)
                goto err_add_raw;

        /* try adding "/sys/firmware/qemu_fw_cfg/by_name/" symlink */
        fw_cfg_build_symlink(fw_cfg_fname_kset, &entry->kobj, entry->name);

        /* success, add entry to global cache */
        fw_cfg_sysfs_cache_enlist(entry);
        return 0;

err_add_raw:
        kobject_del(&entry->kobj);
err_register:
        kfree(entry);
        return err;
}

/* iterate over all fw_cfg directory entries, registering each one */
static int fw_cfg_register_dir_entries(void)
{
        int ret = 0;
        __be32 files_count;
        u32 count, i;
        struct fw_cfg_file *dir;
        size_t dir_size;

        ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, &files_count,
                        0, sizeof(files_count));
        if (ret < 0)
                return ret;

        count = be32_to_cpu(files_count);
        dir_size = count * sizeof(struct fw_cfg_file);

        dir = kmalloc(dir_size, GFP_KERNEL);
        if (!dir)
                return -ENOMEM;

        ret = fw_cfg_read_blob(FW_CFG_FILE_DIR, dir,
                        sizeof(files_count), dir_size);
        if (ret < 0)
                goto end;

        for (i = 0; i < count; i++) {
                ret = fw_cfg_register_file(&dir[i]);
                if (ret)
                        break;
        }

end:
        kfree(dir);
        return ret;
}

/* unregister top-level or by_key folder */
static inline void fw_cfg_kobj_cleanup(struct kobject *kobj)
{
        kobject_del(kobj);
        kobject_put(kobj);
}

static int fw_cfg_sysfs_probe(struct platform_device *pdev)
{
        int err;
        __le32 rev;

        /* NOTE: If we supported multiple fw_cfg devices, we'd first create
         * a subdirectory named after e.g. pdev->id, then hang per-device
         * by_key (and by_name) subdirectories underneath it. However, only
         * one fw_cfg device exist system-wide, so if one was already found
         * earlier, we might as well stop here.
         */
        if (fw_cfg_sel_ko)
                return -EBUSY;

        /* create by_key and by_name subdirs of /sys/firmware/qemu_fw_cfg/ */
        err = -ENOMEM;
        fw_cfg_sel_ko = kobject_create_and_add("by_key", fw_cfg_top_ko);
        if (!fw_cfg_sel_ko)
                goto err_sel;
        fw_cfg_fname_kset = kset_create_and_add("by_name", NULL, fw_cfg_top_ko);
        if (!fw_cfg_fname_kset)
                goto err_name;

        /* initialize fw_cfg device i/o from platform data */
        err = fw_cfg_do_platform_probe(pdev);
        if (err)
                goto err_probe;

        /* get revision number, add matching top-level attribute */
        err = fw_cfg_read_blob(FW_CFG_ID, &rev, 0, sizeof(rev));
        if (err < 0)
                goto err_probe;

        fw_cfg_rev = le32_to_cpu(rev);
        err = sysfs_create_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
        if (err)
                goto err_rev;

        /* process fw_cfg file directory entry, registering each file */
        err = fw_cfg_register_dir_entries();
        if (err)
                goto err_dir;

        /* success */
        pr_debug("fw_cfg: loaded.\n");
        return 0;

err_dir:
        fw_cfg_sysfs_cache_cleanup();
        sysfs_remove_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
err_rev:
        fw_cfg_io_cleanup();
err_probe:
        fw_cfg_kset_unregister_recursive(fw_cfg_fname_kset);
err_name:
        fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
err_sel:
        return err;
}

static int fw_cfg_sysfs_remove(struct platform_device *pdev)
{
        pr_debug("fw_cfg: unloading.\n");
        fw_cfg_sysfs_cache_cleanup();
        sysfs_remove_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
        fw_cfg_io_cleanup();
        fw_cfg_kset_unregister_recursive(fw_cfg_fname_kset);
        fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
        return 0;
}

static const struct of_device_id fw_cfg_sysfs_mmio_match[] = {
        { .compatible = "qemu,fw-cfg-mmio", },
        {},
};
MODULE_DEVICE_TABLE(of, fw_cfg_sysfs_mmio_match);

#ifdef CONFIG_ACPI
static const struct acpi_device_id fw_cfg_sysfs_acpi_match[] = {
        { FW_CFG_ACPI_DEVICE_ID, },
        {},
};
MODULE_DEVICE_TABLE(acpi, fw_cfg_sysfs_acpi_match);
#endif

static struct platform_driver fw_cfg_sysfs_driver = {
        .probe = fw_cfg_sysfs_probe,
        .remove = fw_cfg_sysfs_remove,
        .driver = {
                .name = "fw_cfg",
                .of_match_table = fw_cfg_sysfs_mmio_match,
                .acpi_match_table = ACPI_PTR(fw_cfg_sysfs_acpi_match),
        },
};

#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE

static struct platform_device *fw_cfg_cmdline_dev;

/* this probably belongs in e.g. include/linux/types.h,
 * but right now we are the only ones doing it...
 */
#ifdef CONFIG_PHYS_ADDR_T_64BIT
#define __PHYS_ADDR_PREFIX "ll"
#else
#define __PHYS_ADDR_PREFIX ""
#endif

/* use special scanf/printf modifier for phys_addr_t, resource_size_t */
#define PH_ADDR_SCAN_FMT "@%" __PHYS_ADDR_PREFIX "i%n" \
                         ":%" __PHYS_ADDR_PREFIX "i" \
                         ":%" __PHYS_ADDR_PREFIX "i%n" \
                         ":%" __PHYS_ADDR_PREFIX "i%n"

#define PH_ADDR_PR_1_FMT "0x%" __PHYS_ADDR_PREFIX "x@" \
                         "0x%" __PHYS_ADDR_PREFIX "x"

#define PH_ADDR_PR_3_FMT PH_ADDR_PR_1_FMT \
                         ":%" __PHYS_ADDR_PREFIX "u" \
                         ":%" __PHYS_ADDR_PREFIX "u"

#define PH_ADDR_PR_4_FMT PH_ADDR_PR_3_FMT \
                         ":%" __PHYS_ADDR_PREFIX "u"

static int fw_cfg_cmdline_set(const char *arg, const struct kernel_param *kp)
{
        struct resource res[4] = {};
        char *str;
        phys_addr_t base;
        resource_size_t size, ctrl_off, data_off, dma_off;
        int processed, consumed = 0;

        /* only one fw_cfg device can exist system-wide, so if one
         * was processed on the command line already, we might as
         * well stop here.
         */
        if (fw_cfg_cmdline_dev) {
                /* avoid leaking previously registered device */
                platform_device_unregister(fw_cfg_cmdline_dev);
                return -EINVAL;
        }

        /* consume "<size>" portion of command line argument */
        size = memparse(arg, &str);

        /* get "@<base>[:<ctrl_off>:<data_off>[:<dma_off>]]" chunks */
        processed = sscanf(str, PH_ADDR_SCAN_FMT,
                           &base, &consumed,
                           &ctrl_off, &data_off, &consumed,
                           &dma_off, &consumed);

        /* sscanf() must process precisely 1, 3 or 4 chunks:
         * <base> is mandatory, optionally followed by <ctrl_off>
         * and <data_off>, and <dma_off>;
         * there must be no extra characters after the last chunk,
         * so str[consumed] must be '\0'.
         */
        if (str[consumed] ||
            (processed != 1 && processed != 3 && processed != 4))
                return -EINVAL;

        res[0].start = base;
        res[0].end = base + size - 1;
        res[0].flags = !strcmp(kp->name, "mmio") ? IORESOURCE_MEM :
                                                   IORESOURCE_IO;

        /* insert register offsets, if provided */
        if (processed > 1) {
                res[1].name = "ctrl";
                res[1].start = ctrl_off;
                res[1].flags = IORESOURCE_REG;
                res[2].name = "data";
                res[2].start = data_off;
                res[2].flags = IORESOURCE_REG;
        }
        if (processed > 3) {
                res[3].name = "dma";
                res[3].start = dma_off;
                res[3].flags = IORESOURCE_REG;
        }

        /* "processed" happens to nicely match the number of resources
         * we need to pass in to this platform device.
         */
        fw_cfg_cmdline_dev = platform_device_register_simple("fw_cfg",
                                        PLATFORM_DEVID_NONE, res, processed);

        return PTR_ERR_OR_ZERO(fw_cfg_cmdline_dev);
}

static int fw_cfg_cmdline_get(char *buf, const struct kernel_param *kp)
{
        /* stay silent if device was not configured via the command
         * line, or if the parameter name (ioport/mmio) doesn't match
         * the device setting
         */
        if (!fw_cfg_cmdline_dev ||
            (!strcmp(kp->name, "mmio") ^
             (fw_cfg_cmdline_dev->resource[0].flags == IORESOURCE_MEM)))
                return 0;

        switch (fw_cfg_cmdline_dev->num_resources) {
        case 1:
                return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_1_FMT,
                                resource_size(&fw_cfg_cmdline_dev->resource[0]),
                                fw_cfg_cmdline_dev->resource[0].start);
        case 3:
                return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_3_FMT,
                                resource_size(&fw_cfg_cmdline_dev->resource[0]),
                                fw_cfg_cmdline_dev->resource[0].start,
                                fw_cfg_cmdline_dev->resource[1].start,
                                fw_cfg_cmdline_dev->resource[2].start);
        case 4:
                return snprintf(buf, PAGE_SIZE, PH_ADDR_PR_4_FMT,
                                resource_size(&fw_cfg_cmdline_dev->resource[0]),
                                fw_cfg_cmdline_dev->resource[0].start,
                                fw_cfg_cmdline_dev->resource[1].start,
                                fw_cfg_cmdline_dev->resource[2].start,
                                fw_cfg_cmdline_dev->resource[3].start);
        }

        /* Should never get here */
        WARN(1, "Unexpected number of resources: %d\n",
                fw_cfg_cmdline_dev->num_resources);
        return 0;
}

static const struct kernel_param_ops fw_cfg_cmdline_param_ops = {
        .set = fw_cfg_cmdline_set,
        .get = fw_cfg_cmdline_get,
};

device_param_cb(ioport, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);
device_param_cb(mmio, &fw_cfg_cmdline_param_ops, NULL, S_IRUSR);

#endif /* CONFIG_FW_CFG_SYSFS_CMDLINE */

static int __init fw_cfg_sysfs_init(void)
{
        int ret;

        /* create /sys/firmware/qemu_fw_cfg/ top level directory */
        fw_cfg_top_ko = kobject_create_and_add("qemu_fw_cfg", firmware_kobj);
        if (!fw_cfg_top_ko)
                return -ENOMEM;

        ret = platform_driver_register(&fw_cfg_sysfs_driver);
        if (ret)
                fw_cfg_kobj_cleanup(fw_cfg_top_ko);

        return ret;
}

static void __exit fw_cfg_sysfs_exit(void)
{
        platform_driver_unregister(&fw_cfg_sysfs_driver);

#ifdef CONFIG_FW_CFG_SYSFS_CMDLINE
        platform_device_unregister(fw_cfg_cmdline_dev);
#endif

        /* clean up /sys/firmware/qemu_fw_cfg/ */
        fw_cfg_kobj_cleanup(fw_cfg_top_ko);
}

module_init(fw_cfg_sysfs_init);
module_exit(fw_cfg_sysfs_exit);