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// SPDX-License-Identifier: GPL-2.0
// General Purpose SPI multiplexer
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mux/consumer.h>
#include <linux/slab.h>
#include <linux/spi/spi.h>
#define SPI_MUX_NO_CS ((unsigned int)-1)
* DOC: Driver description
* This driver supports a MUX on an SPI bus. This can be useful when you need
* more chip selects than the hardware peripherals support, or than are
* available in a particular board setup.
* The driver will create an additional SPI controller. Devices added under the
* mux will be handled as 'chip selects' on this controller.
* struct spi_mux_priv - the basic spi_mux structure
* @spi: pointer to the device struct attached to the parent
* spi controller
* @current_cs: The current chip select set in the mux
* @child_msg_complete: The mux replaces the complete callback in the child's
* message to its own callback; this field is used by the
* driver to store the child's callback during a transfer
* @child_msg_context: Used to store the child's context to the callback
* @child_msg_dev: Used to store the spi_device pointer to the child
* @mux: mux_control structure used to provide chip selects for
* downstream spi devices
struct spi_mux_priv {
struct spi_device *spi;
unsigned int current_cs;
void (*child_msg_complete)(void *context);
void *child_msg_context;
struct spi_device *child_msg_dev;
struct mux_control *mux;
/* should not get called when the parent controller is doing a transfer */
static int spi_mux_select(struct spi_device *spi)
struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
int ret;
ret = mux_control_select(priv->mux, spi->chip_select);
if (ret)
return ret;
if (priv->current_cs == spi->chip_select)
return 0;
dev_dbg(&priv->spi->dev, "setting up the mux for cs %d\n",
/* copy the child device's settings except for the cs */
priv->spi->max_speed_hz = spi->max_speed_hz;
priv->spi->mode = spi->mode;
priv->spi->bits_per_word = spi->bits_per_word;
priv->current_cs = spi->chip_select;
return 0;
static int spi_mux_setup(struct spi_device *spi)
struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
* can be called multiple times, won't do a valid setup now but we will
* change the settings when we do a transfer (necessary because we
* can't predict from which device it will be anyway)
return spi_setup(priv->spi);
static void spi_mux_complete_cb(void *context)
struct spi_mux_priv *priv = (struct spi_mux_priv *)context;
struct spi_controller *ctlr = spi_get_drvdata(priv->spi);
struct spi_message *m = ctlr->cur_msg;
m->complete = priv->child_msg_complete;
m->context = priv->child_msg_context;
m->spi = priv->child_msg_dev;
static int spi_mux_transfer_one_message(struct spi_controller *ctlr,
struct spi_message *m)
struct spi_mux_priv *priv = spi_controller_get_devdata(ctlr);
struct spi_device *spi = m->spi;
int ret;
ret = spi_mux_select(spi);
if (ret)
return ret;
* Replace the complete callback, context and spi_device with our own
* pointers. Save originals
priv->child_msg_complete = m->complete;
priv->child_msg_context = m->context;
priv->child_msg_dev = m->spi;
m->complete = spi_mux_complete_cb;
m->context = priv;
m->spi = priv->spi;
/* do the transfer */
return spi_async(priv->spi, m);
static int spi_mux_probe(struct spi_device *spi)
struct spi_controller *ctlr;
struct spi_mux_priv *priv;
int ret;
ctlr = spi_alloc_master(&spi->dev, sizeof(*priv));
if (!ctlr)
return -ENOMEM;
spi_set_drvdata(spi, ctlr);
priv = spi_controller_get_devdata(ctlr);
priv->spi = spi;
priv->mux = devm_mux_control_get(&spi->dev, NULL);
if (IS_ERR(priv->mux)) {
ret = PTR_ERR(priv->mux);
if (ret != -EPROBE_DEFER)
dev_err(&spi->dev, "failed to get control-mux\n");
goto err_put_ctlr;
priv->current_cs = SPI_MUX_NO_CS;
/* supported modes are the same as our parent's */
ctlr->mode_bits = spi->controller->mode_bits;
ctlr->flags = spi->controller->flags;
ctlr->transfer_one_message = spi_mux_transfer_one_message;
ctlr->setup = spi_mux_setup;
ctlr->num_chipselect = mux_control_states(priv->mux);
ctlr->bus_num = -1;
ctlr->dev.of_node = spi->dev.of_node;
ret = devm_spi_register_controller(&spi->dev, ctlr);
if (ret)
goto err_put_ctlr;
return 0;
return ret;
static const struct of_device_id spi_mux_of_match[] = {
{ .compatible = "spi-mux" },
{ }
static struct spi_driver spi_mux_driver = {
.probe = spi_mux_probe,
.driver = {
.name = "spi-mux",
.of_match_table = spi_mux_of_match,