d8f388d8dc
This adds a simple sysfs interface for GPIOs.
/sys/class/gpio
/export ... asks the kernel to export a GPIO to userspace
/unexport ... to return a GPIO to the kernel
/gpioN ... for each exported GPIO #N
/value ... always readable, writes fail for input GPIOs
/direction ... r/w as: in, out (default low); write high, low
/gpiochipN ... for each gpiochip; #N is its first GPIO
/base ... (r/o) same as N
/label ... (r/o) descriptive, not necessarily unique
/ngpio ... (r/o) number of GPIOs; numbered N .. N+(ngpio - 1)
GPIOs claimed by kernel code may be exported by its owner using a new
gpio_export() call, which should be most useful for driver debugging.
Such exports may optionally be done without a "direction" attribute.
Userspace may ask to take over a GPIO by writing to a sysfs control file,
helping to cope with incomplete board support or other "one-off"
requirements that don't merit full kernel support:
echo 23 > /sys/class/gpio/export
... will gpio_request(23, "sysfs") and gpio_export(23);
use /sys/class/gpio/gpio-23/direction to (re)configure it,
when that GPIO can be used as both input and output.
echo 23 > /sys/class/gpio/unexport
... will gpio_free(23), when it was exported as above
The extra D-space footprint is a few hundred bytes, except for the sysfs
resources associated with each exported GPIO. The additional I-space
footprint is about two thirds of the current size of gpiolib (!). Since
no /dev node creation is involved, no "udev" support is needed.
Related changes:
* This adds a device pointer to "struct gpio_chip". When GPIO
providers initialize that, sysfs gpio class devices become children of
that device instead of being "virtual" devices.
* The (few) gpio_chip providers which have such a device node have
been updated.
* Some gpio_chip drivers also needed to update their module "owner"
field ... for which missing kerneldoc was added.
* Some gpio_chips don't support input GPIOs. Those GPIOs are now
flagged appropriately when the chip is registered.
Based on previous patches, and discussion both on and off LKML.
A Documentation/ABI/testing/sysfs-gpio update is ready to submit once this
merges to mainline.
[akpm@linux-foundation.org: a few maintenance build fixes]
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Guennadi Liakhovetski <g.liakhovetski@pengutronix.de>
Cc: Greg KH <greg@kroah.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
112 lines
2.2 KiB
C
112 lines
2.2 KiB
C
#ifndef __LINUX_GPIO_H
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#define __LINUX_GPIO_H
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/* see Documentation/gpio.txt */
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#ifdef CONFIG_GENERIC_GPIO
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#include <asm/gpio.h>
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#else
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#include <linux/types.h>
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#include <linux/errno.h>
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/*
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* Some platforms don't support the GPIO programming interface.
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*
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* In case some driver uses it anyway (it should normally have
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* depended on GENERIC_GPIO), these routines help the compiler
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* optimize out much GPIO-related code ... or trigger a runtime
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* warning when something is wrongly called.
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*/
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static inline int gpio_is_valid(int number)
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{
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return 0;
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}
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static inline int gpio_request(unsigned gpio, const char *label)
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{
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return -ENOSYS;
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}
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static inline void gpio_free(unsigned gpio)
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{
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/* GPIO can never have been requested */
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WARN_ON(1);
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}
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static inline int gpio_direction_input(unsigned gpio)
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{
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return -ENOSYS;
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}
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static inline int gpio_direction_output(unsigned gpio, int value)
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{
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return -ENOSYS;
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}
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static inline int gpio_get_value(unsigned gpio)
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{
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/* GPIO can never have been requested or set as {in,out}put */
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WARN_ON(1);
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return 0;
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}
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static inline void gpio_set_value(unsigned gpio, int value)
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{
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/* GPIO can never have been requested or set as output */
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WARN_ON(1);
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}
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static inline int gpio_cansleep(unsigned gpio)
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{
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/* GPIO can never have been requested or set as {in,out}put */
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WARN_ON(1);
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return 0;
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}
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static inline int gpio_get_value_cansleep(unsigned gpio)
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{
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/* GPIO can never have been requested or set as {in,out}put */
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WARN_ON(1);
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return 0;
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}
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static inline void gpio_set_value_cansleep(unsigned gpio, int value)
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{
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/* GPIO can never have been requested or set as output */
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WARN_ON(1);
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}
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static inline int gpio_export(unsigned gpio, bool direction_may_change)
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{
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/* GPIO can never have been requested or set as {in,out}put */
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WARN_ON(1);
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return -EINVAL;
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}
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static inline void gpio_unexport(unsigned gpio)
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{
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/* GPIO can never have been exported */
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WARN_ON(1);
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}
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static inline int gpio_to_irq(unsigned gpio)
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{
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/* GPIO can never have been requested or set as input */
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WARN_ON(1);
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return -EINVAL;
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}
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static inline int irq_to_gpio(unsigned irq)
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{
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/* irq can never have been returned from gpio_to_irq() */
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WARN_ON(1);
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return -EINVAL;
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}
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#endif
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#endif /* __LINUX_GPIO_H */
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