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authorDavid Brownell <dbrownell@users.sourceforge.net>2008-09-13 05:33:20 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-09-13 17:41:52 -0400
commit9f986a8cdf94a5855201cf67db6ffdf926bc4cd9 (patch)
tree7c74f8727f2baa389f2305b43a9e3f21bb650c77 /Documentation/ABI
parent5bead2a0680687b9576d57c177988e8aa082b922 (diff)
Documentation/ABI: /sys/class/gpio
Provide summary ABI docs about the /sys/class/gpio files. Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Cc: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1What: /sys/class/gpio/
2Date: July 2008
3KernelVersion: 2.6.27
4Contact: David Brownell <dbrownell@users.sourceforge.net>
5Description:
6
7 As a Kconfig option, individual GPIO signals may be accessed from
8 userspace. GPIOs are only made available to userspace by an explicit
9 "export" operation. If a given GPIO is not claimed for use by
10 kernel code, it may be exported by userspace (and unexported later).
11 Kernel code may export it for complete or partial access.
12
13 GPIOs are identified as they are inside the kernel, using integers in
14 the range 0..INT_MAX. See Documentation/gpio.txt for more information.
15
16 /sys/class/gpio
17 /export ... asks the kernel to export a GPIO to userspace
18 /unexport ... to return a GPIO to the kernel
19 /gpioN ... for each exported GPIO #N
20 /value ... always readable, writes fail for input GPIOs
21 /direction ... r/w as: in, out (default low); write: high, low
22 /gpiochipN ... for each gpiochip; #N is its first GPIO
23 /base ... (r/o) same as N
24 /label ... (r/o) descriptive, not necessarily unique
25 /ngpio ... (r/o) number of GPIOs; numbered N to N + (ngpio - 1)
26