gpiolib: allow exported GPIO nodes to be named using sysfs links
Commit 926b663ce8215ba448960e1ff6e58b67a2c3b99b (gpiolib: allow GPIOs to
be named) already provides naming on the chip level. This patch provides
more flexibility by allowing multiple names where ever in sysfs on a per
GPIO basis.
Adapted from David Brownell's comments on a similar concept:
http://lkml.org/lkml/2009/4/20/203.
[randy.dunlap@oracle.com: fix build for CONFIG_GENERIC_GPIO=n]
Signed-off-by: Jani Nikula <ext-jani.1.nikula@nokia.com>
Acked-by: David Brownell <david-b@pacbell.net>
Cc: Daniel Silverstone <dsilvers@simtec.co.uk>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index e4b6985..566edaa 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -555,6 +555,11 @@
/* reverse gpio_export() */
void gpio_unexport();
+ /* create a sysfs link to an exported GPIO node */
+ int gpio_export_link(struct device *dev, const char *name,
+ unsigned gpio)
+
+
After a kernel driver requests a GPIO, it may only be made available in
the sysfs interface by gpio_export(). The driver can control whether the
signal direction may change. This helps drivers prevent userspace code
@@ -563,3 +568,8 @@
This explicit exporting can help with debugging (by making some kinds
of experiments easier), or can provide an always-there interface that's
suitable for documenting as part of a board support package.
+
+After the GPIO has been exported, gpio_export_link() allows creating
+symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can
+use this to provide the interface under their own device in sysfs with
+a descriptive name.
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 51a8d41..aef6b3d 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -505,6 +505,51 @@
}
/**
+ * gpio_export_link - create a sysfs link to an exported GPIO node
+ * @dev: device under which to create symlink
+ * @name: name of the symlink
+ * @gpio: gpio to create symlink to, already exported
+ *
+ * Set up a symlink from /sys/.../dev/name to /sys/class/gpio/gpioN
+ * node. Caller is responsible for unlinking.
+ *
+ * Returns zero on success, else an error.
+ */
+int gpio_export_link(struct device *dev, const char *name, unsigned gpio)
+{
+ struct gpio_desc *desc;
+ int status = -EINVAL;
+
+ if (!gpio_is_valid(gpio))
+ goto done;
+
+ mutex_lock(&sysfs_lock);
+
+ desc = &gpio_desc[gpio];
+
+ if (test_bit(FLAG_EXPORT, &desc->flags)) {
+ struct device *tdev;
+
+ tdev = class_find_device(&gpio_class, NULL, desc, match_export);
+ if (tdev != NULL) {
+ status = sysfs_create_link(&dev->kobj, &tdev->kobj,
+ name);
+ } else {
+ status = -ENODEV;
+ }
+ }
+
+ mutex_unlock(&sysfs_lock);
+
+done:
+ if (status)
+ pr_debug("%s: gpio%d status %d\n", __func__, gpio, status);
+
+ return status;
+}
+EXPORT_SYMBOL_GPL(gpio_export_link);
+
+/**
* gpio_unexport - reverse effect of gpio_export()
* @gpio: gpio to make unavailable
*
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index d6c379d..9cca3785 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -141,6 +141,8 @@
* but more typically is configured entirely from userspace.
*/
extern int gpio_export(unsigned gpio, bool direction_may_change);
+extern int gpio_export_link(struct device *dev, const char *name,
+ unsigned gpio);
extern void gpio_unexport(unsigned gpio);
#endif /* CONFIG_GPIO_SYSFS */
@@ -185,6 +187,12 @@
return -ENOSYS;
}
+static inline int gpio_export_link(struct device *dev, const char *name,
+ unsigned gpio)
+{
+ return -ENOSYS;
+}
+
static inline void gpio_unexport(unsigned gpio)
{
}
diff --git a/include/linux/gpio.h b/include/linux/gpio.h
index e10c49a..059bd18 100644
--- a/include/linux/gpio.h
+++ b/include/linux/gpio.h
@@ -12,6 +12,8 @@
#include <linux/types.h>
#include <linux/errno.h>
+struct device;
+
/*
* Some platforms don't support the GPIO programming interface.
*
@@ -89,6 +91,15 @@
return -EINVAL;
}
+static inline int gpio_export_link(struct device *dev, const char *name,
+ unsigned gpio)
+{
+ /* GPIO can never have been exported */
+ WARN_ON(1);
+ return -EINVAL;
+}
+
+
static inline void gpio_unexport(unsigned gpio)
{
/* GPIO can never have been exported */
