Commit a4177ee7 authored by Jani Nikula's avatar Jani Nikula Committed by Linus Torvalds

gpiolib: allow exported GPIO nodes to be named using sysfs links

Commit 926b663c (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: default avatarJani Nikula <ext-jani.1.nikula@nokia.com>
Acked-by: default avatarDavid Brownell <david-b@pacbell.net>
Cc: Daniel Silverstone <dsilvers@simtec.co.uk>
Signed-off-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d8c1acb1
......@@ -555,6 +555,11 @@ requested using gpio_request():
/* 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 @@ from accidentally clobbering important system state.
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.
......@@ -504,6 +504,51 @@ static int match_export(struct device *dev, void *data)
return dev_get_drvdata(dev) == data;
}
/**
* 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
......
......@@ -141,6 +141,8 @@ extern int __gpio_to_irq(unsigned gpio);
* 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 @@ static inline int gpio_export(unsigned gpio, bool direction_may_change)
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)
{
}
......
......@@ -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 @@ static inline int gpio_export(unsigned gpio, bool direction_may_change)
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 */
......
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