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

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

Documentation/gpio.txt

+10 −0
Original line number Diff line number Diff line
@@ -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.

drivers/gpio/gpiolib.c

+45 −0
Original line number Diff line number Diff line
@@ -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

include/asm-generic/gpio.h

+8 −0
Original line number Diff line number Diff line
@@ -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)

{

}

include/linux/gpio.h

+11 −0
Original line number Diff line number Diff line
@@ -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 */