[PATCH] spi: Add option to bind spidev to all chipselects

Michal Suchanek
2015-05-13T09:34:48Z

Bypass the check if CS is in use for spidev devices if CONFIG_SPIDEV_SHADOW is
set. Rename spidev devices to avoid sysfs conflict.

This allows dynamically loading SPI device overlays or communicating
with SPI devices configured by a kernel driver from userspace.

Signed-off-by: Michal Suchanek <hramrach@gmail.com>
---
drivers/spi/Kconfig | 13 +++++++++
drivers/spi/spi.c | 74 ++++++++++++++++++++++++++++++++++---------------
include/linux/spi/spi.h | 1 +
3 files changed, 65 insertions(+), 23 deletions(-)

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 198f96b..b477828 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -651,6 +651,19 @@ config SPI_SPIDEV
Note that this application programming interface is EXPERIMENTAL
and hence SUBJECT TO CHANGE WITHOUT NOTICE while it stabilizes.

+config SPIDEV_SHADOW
+ depends on SPI_SPIDEV
+ bool "Allow spidev access to configured SPI devices (DANGEROUS)"
+ help
+ This creates a spidev device node for every chipselect.
+
+ It is possible to access even SPI devices which are in use by a
+ kernel driver. This allows invoking features not in use by the kernel
+ or checking device state from userspace when the kernel driver fails.
+
+ Sending out-of-order messages to the device or reconfiguring the
+ device might cause driver failure. DANGEROUS
+
config SPI_TLE62X0
tristate "Infineon TLE62X0 (for power switching)"
depends on SYSFS
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index e6ca46e..b48a0dc 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -254,16 +254,23 @@ struct spi_device *spi_alloc_device(struct spi_master *master)
}
EXPORT_SYMBOL_GPL(spi_alloc_device);

-static void spi_dev_set_name(struct spi_device *spi)
+static void spi_dev_set_name(struct spi_device *spi, const char * alias)
{
struct acpi_device *adev = ACPI_COMPANION(&spi->dev);

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

- dev_set_name(&spi->dev, "%s.%u", dev_name(&spi->master->dev),
+ if (alias)
+ dev_set_name(&spi->dev, "%s%u.%u", alias, spi->master->bus_num,
+ spi->chip_select);
+ else
+ dev_set_name(&spi->dev, "%s.%u", dev_name(&spi->master->dev),
spi->chip_select);
}

@@ -272,22 +279,25 @@ 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)
+ if (spi->master == new_spi->master
+ && spi->chip_select == new_spi->chip_select
+#ifdef CONFIG_SPIDEV_SHADOW
+ && !spi->shadow && !new_spi->shadow
+#endif
+ )
return -EBUSY;
return 0;
}

/**
- * spi_add_device - Add spi_device allocated with spi_alloc_device
+ * spi_add_device_alias - Add spi_device allocated with spi_alloc_device
+ * possibly even when device for the CS exists.
* @spi: spi_device to register
+ * @alias: string used as device name prefix or NULL
*
- * Companion function to spi_alloc_device. Devices allocated with
- * spi_alloc_device can be added onto the spi bus with this function.
- *
- * Returns 0 on success; negative errno on failure
+ * See spi_add_device
*/
-int spi_add_device(struct spi_device *spi)
+static inline int spi_add_device_alias(struct spi_device *spi, const char * alias)
{
static DEFINE_MUTEX(spi_add_lock);
struct spi_master *master = spi->master;
@@ -303,7 +313,8 @@ int spi_add_device(struct spi_device *spi)
}

/* Set the bus ID string */
- spi_dev_set_name(spi);
+ spi_dev_set_name(spi, alias);
+ spi->shadow = !!alias;

/* We need to make sure there's no other device with this
* chipselect **BEFORE** we call setup(), else we'll trash
@@ -321,15 +332,17 @@ int spi_add_device(struct spi_device *spi)
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;
+ if (!alias) {
+ /* 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 */
@@ -344,6 +357,20 @@ done:
mutex_unlock(&spi_add_lock);
return status;
}
+
+/**
+ * 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.
+ *
+ * Returns 0 on success; negative errno on failure
+ */
+int spi_add_device(struct spi_device *spi)
+{
+ return spi_add_device_alias(spi, NULL);
+}
EXPORT_SYMBOL_GPL(spi_add_device);

/**
@@ -1400,6 +1427,7 @@ static void spidev_register_devices(struct spi_master *master)
spi->chip_select = i;
strlcpy(spi->modalias, "spidev", sizeof(spi->modalias));

+#ifndef CONFIG_SPIDEV_SHADOW
/*
* This is far from perfect since an addition might be
* done between here and the call to spi_add_device,
@@ -1418,8 +1446,8 @@ static void spidev_register_devices(struct spi_master *master)
spi_dev_put(spi);
continue;
}
-
- if (spi_add_device(spi)) {
+#endif /* CONFIG_SPIDEV_SHADOW */
+ if (spi_add_device_alias(spi, "spidev")) {
dev_err(&master->dev, "Couldn't add spidev device\n");
spi_dev_put(spi);
}
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index d673072..8368714 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -97,6 +97,7 @@ struct spi_device {
void *controller_data;
char modalias[SPI_NAME_SIZE];
int cs_gpio; /* chip select gpio */
+ int shadow; /* ignore when determining if CS is in use */

/*
* likely need more hooks for more protocol options affecting how
--
2.1.4