drivers/spi/spi-mux.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 //
   3 // General Purpose SPI multiplexer
   4
   5 #include <linux/err.h>
   6 #include <linux/kernel.h>
   7 #include <linux/module.h>
   8 #include <linux/mux/consumer.h>
   9 #include <linux/slab.h>
  10 #include <linux/spi/spi.h>
  11
  12 #define SPI_MUX_NO_CS   ((unsigned int)-1)
  13
  14 /**
  15  * DOC: Driver description
  16  *
  17  * This driver supports a MUX on an SPI bus. This can be useful when you need
  18  * more chip selects than the hardware peripherals support, or than are
  19  * available in a particular board setup.
  20  *
  21  * The driver will create an additional SPI controller. Devices added under the
  22  * mux will be handled as 'chip selects' on this controller.
  23  */
  24
  25 /**
  26  * struct spi_mux_priv - the basic spi_mux structure
  27  * @spi:                pointer to the device struct attached to the parent
  28  *                      spi controller
  29  * @current_cs:         The current chip select set in the mux
  30  * @child_msg_complete: The mux replaces the complete callback in the child's
  31  *                      message to its own callback; this field is used by the
  32  *                      driver to store the child's callback during a transfer
  33  * @child_msg_context:  Used to store the child's context to the callback
  34  * @child_msg_dev:      Used to store the spi_device pointer to the child
  35  * @mux:                mux_control structure used to provide chip selects for
  36  *                      downstream spi devices
  37  */
  38 struct spi_mux_priv {
  39         struct spi_device       *spi;
  40         unsigned int            current_cs;
  41
  42         void                    (*child_msg_complete)(void *context);
  43         void                    *child_msg_context;
  44         struct spi_device       *child_msg_dev;
  45         struct mux_control      *mux;
  46 };
  47
  48 /* should not get called when the parent controller is doing a transfer */
  49 static int spi_mux_select(struct spi_device *spi)
  50 {
  51         struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
  52         int ret;
  53
  54         ret = mux_control_select(priv->mux, spi->chip_select);
  55         if (ret)
  56                 return ret;
  57
  58         if (priv->current_cs == spi->chip_select)
  59                 return 0;
  60
  61         dev_dbg(&priv->spi->dev, "setting up the mux for cs %d\n",
  62                 spi->chip_select);
  63
  64         /* copy the child device's settings except for the cs */
  65         priv->spi->max_speed_hz = spi->max_speed_hz;
  66         priv->spi->mode = spi->mode;
  67         priv->spi->bits_per_word = spi->bits_per_word;
  68
  69         priv->current_cs = spi->chip_select;
  70
  71         return 0;
  72 }
  73
  74 static int spi_mux_setup(struct spi_device *spi)
  75 {
  76         struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
  77
  78         /*
  79          * can be called multiple times, won't do a valid setup now but we will
  80          * change the settings when we do a transfer (necessary because we
  81          * can't predict from which device it will be anyway)
  82          */
  83         return spi_setup(priv->spi);
  84 }
  85
  86 static void spi_mux_complete_cb(void *context)
  87 {
  88         struct spi_mux_priv *priv = (struct spi_mux_priv *)context;
  89         struct spi_controller *ctlr = spi_get_drvdata(priv->spi);
  90         struct spi_message *m = ctlr->cur_msg;
  91
  92         m->complete = priv->child_msg_complete;
  93         m->context = priv->child_msg_context;
  94         m->spi = priv->child_msg_dev;
  95         spi_finalize_current_message(ctlr);
  96         mux_control_deselect(priv->mux);
  97 }
  98
  99 static int spi_mux_transfer_one_message(struct spi_controller *ctlr,
 100                                                 struct spi_message *m)
 101 {
 102         struct spi_mux_priv *priv = spi_controller_get_devdata(ctlr);
 103         struct spi_device *spi = m->spi;
 104         int ret;
 105
 106         ret = spi_mux_select(spi);
 107         if (ret)
 108                 return ret;
 109
 110         /*
 111          * Replace the complete callback, context and spi_device with our own
 112          * pointers. Save originals
 113          */
 114         priv->child_msg_complete = m->complete;
 115         priv->child_msg_context = m->context;
 116         priv->child_msg_dev = m->spi;
 117
 118         m->complete = spi_mux_complete_cb;
 119         m->context = priv;
 120         m->spi = priv->spi;
 121
 122         /* do the transfer */
 123         return spi_async(priv->spi, m);
 124 }
 125
 126 static int spi_mux_probe(struct spi_device *spi)
 127 {
 128         struct spi_controller *ctlr;
 129         struct spi_mux_priv *priv;
 130         int ret;
 131
 132         ctlr = spi_alloc_master(&spi->dev, sizeof(*priv));
 133         if (!ctlr)
 134                 return -ENOMEM;
 135
 136         spi_set_drvdata(spi, ctlr);
 137         priv = spi_controller_get_devdata(ctlr);
 138         priv->spi = spi;
 139
 140         priv->mux = devm_mux_control_get(&spi->dev, NULL);
 141         if (IS_ERR(priv->mux)) {
 142                 ret = dev_err_probe(&spi->dev, PTR_ERR(priv->mux),
 143                                     "failed to get control-mux\n");
 144                 goto err_put_ctlr;
 145         }
 146
 147         priv->current_cs = SPI_MUX_NO_CS;
 148
 149         /* supported modes are the same as our parent's */
 150         ctlr->mode_bits = spi->controller->mode_bits;
 151         ctlr->flags = spi->controller->flags;
 152         ctlr->transfer_one_message = spi_mux_transfer_one_message;
 153         ctlr->setup = spi_mux_setup;
 154         ctlr->num_chipselect = mux_control_states(priv->mux);
 155         ctlr->bus_num = -1;
 156         ctlr->dev.of_node = spi->dev.of_node;
 157
 158         ret = devm_spi_register_controller(&spi->dev, ctlr);
 159         if (ret)
 160                 goto err_put_ctlr;
 161
 162         return 0;
 163
 164 err_put_ctlr:
 165         spi_controller_put(ctlr);
 166
 167         return ret;
 168 }
 169
 170 static const struct of_device_id spi_mux_of_match[] = {
 171         { .compatible = "spi-mux" },
 172         { }
 173 };
 174
 175 static struct spi_driver spi_mux_driver = {
 176         .probe  = spi_mux_probe,
 177         .driver = {
 178                 .name   = "spi-mux",
 179                 .of_match_table = spi_mux_of_match,
 180         },
 181 };
 182
 183 module_spi_driver(spi_mux_driver);
 184
 185 MODULE_DESCRIPTION("SPI multiplexer");
 186 MODULE_LICENSE("GPL");