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authorDavid Brownell <dbrownell@users.sourceforge.net>2008-07-25 01:46:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-07-25 10:53:30 -0700
commitd8f388d8dc8d4f36539dd37c1fff62cc404ea0fc (patch)
treedf8603775c889f29f8a03c77b9f7913bfd90d296 /drivers/gpio/Kconfig
parent8b6dd986823a8d92ed9f54baa5cef8604d9d9d44 (diff)
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gpio: sysfs interface
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>
Diffstat (limited to 'drivers/gpio/Kconfig')
-rw-r--r--drivers/gpio/Kconfig15
1 files changed, 15 insertions, 0 deletions
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index fced190..6ec0e35 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -23,6 +23,21 @@ config DEBUG_GPIO
slower. The diagnostics help catch the type of setup errors
that are most common when setting up new platforms or boards.
+config GPIO_SYSFS
+ bool "/sys/class/gpio/... (sysfs interface)"
+ depends on SYSFS && EXPERIMENTAL
+ help
+ Say Y here to add a sysfs interface for GPIOs.
+
+ This is mostly useful to work around omissions in a system's
+ kernel support. Those are common in custom and semicustom
+ hardware assembled using standard kernels with a minimum of
+ custom patches. In those cases, userspace code may import
+ a given GPIO from the kernel, if no kernel driver requested it.
+
+ Kernel drivers may also request that a particular GPIO be
+ exported to userspace; this can be useful when debugging.
+
# put expanders in the right section, in alphabetical order
comment "I2C GPIO expanders:"