9f986a8cdf
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>
27 lines
1.1 KiB
Plaintext
27 lines
1.1 KiB
Plaintext
What: /sys/class/gpio/
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Date: July 2008
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KernelVersion: 2.6.27
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Contact: David Brownell <dbrownell@users.sourceforge.net>
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Description:
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As a Kconfig option, individual GPIO signals may be accessed from
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userspace. GPIOs are only made available to userspace by an explicit
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"export" operation. If a given GPIO is not claimed for use by
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kernel code, it may be exported by userspace (and unexported later).
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Kernel code may export it for complete or partial access.
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GPIOs are identified as they are inside the kernel, using integers in
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the range 0..INT_MAX. See Documentation/gpio.txt for more information.
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/sys/class/gpio
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/export ... asks the kernel to export a GPIO to userspace
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/unexport ... to return a GPIO to the kernel
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/gpioN ... for each exported GPIO #N
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/value ... always readable, writes fail for input GPIOs
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/direction ... r/w as: in, out (default low); write: high, low
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/gpiochipN ... for each gpiochip; #N is its first GPIO
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/base ... (r/o) same as N
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/label ... (r/o) descriptive, not necessarily unique
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/ngpio ... (r/o) number of GPIOs; numbered N to N + (ngpio - 1)
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