linux/drivers/spi/spi-mux.c
Peter Rosin a2b02e4623
spi: mux: repair mux usage
It is not valid to cache/short out selection of the mux.

mux_control_select() only locks the mux until mux_control_deselect()
is called. mux_control_deselect() may put the mux in some low power
state or some other user of the mux might select it for other purposes.
These things are probably not happening in the original setting where
this driver was developed, but it is said to be a generic SPI mux.

Also, the mux framework will short out the actual low level muxing
operation when/if that is possible.

Fixes: e9e40543ad ("spi: Add generic SPI multiplexer")
Signed-off-by: Peter Rosin <peda@axentia.se>
Link: https://lore.kernel.org/r/20200525104352.26807-1-peda@axentia.se
Signed-off-by: Mark Brown <broonie@kernel.org>
2020-05-25 13:25:34 +01:00

188 lines
4.8 KiB
C

// 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",
spi->chip_select);
/* 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;
spi_finalize_current_message(ctlr);
mux_control_deselect(priv->mux);
}
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;
err_put_ctlr:
spi_controller_put(ctlr);
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,
},
};
module_spi_driver(spi_mux_driver);
MODULE_DESCRIPTION("SPI multiplexer");
MODULE_LICENSE("GPL");