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Commit ebde7b06 authored by Bernhard Walle's avatar Bernhard Walle Committed by Linus Torvalds
Browse files

Documentation/gpio.txt: explain poll/select usage 



Add a bit more information how to use poll(2) on GPIO value files
correctly. For me it was not clear that I need to poll(2) for
POLLPRI|POLLERR or select(2) for exceptfds.

Signed-off-by: default avatarBernhard Walle <walle@corscience.de>
Signed-off-by: default avatarRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 09c9feb9

Documentation/gpio.txt

+10 −0
Original line number Original line Diff line number Diff line
@@ -617,6 +617,16 @@ and have the following read/write attributes: 
		is configured as an output, this value may be written;

		is configured as an output, this value may be written;

		any nonzero value is treated as high.

		any nonzero value is treated as high.





		If the pin can be configured as interrupt-generating interrupt

		and if it has been configured to generate interrupts (see the

		description of "edge"), you can poll(2) on that file and

		poll(2) will return whenever the interrupt was triggered. If

		you use poll(2), set the events POLLPRI and POLLERR. If you

		use select(2), set the file descriptor in exceptfds. After

		poll(2) returns, either lseek(2) to the beginning of the sysfs

		file and read the new value or close the file and re-open it

		to read the value.



	"edge" ... reads as either "none", "rising", "falling", or

	"edge" ... reads as either "none", "rising", "falling", or

		"both". Write these strings to select the signal edge(s)

		"both". Write these strings to select the signal edge(s)

		that will make poll(2) on the "value" file return.

		that will make poll(2) on the "value" file return.