Commit 7f1e45f4 authored by Huichun Feng's avatar Huichun Feng Committed by Bartosz Golaszewski
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docs: gpio: prefer pread(2) for interrupt reading 



In legacy sysfs GPIO, when using poll(2) on the sysfs GPIO value for
state change awaiting, a subsequent read(2) is required for consuming
the event, which the doc recommends the use of lseek(2) or
close-and-reopen to reset the file offset afterwards.

The recommendations however, require at least 2 syscalls to consume
the event. Gladly, use of pread(2) require only 1 syscall for the
consumption. Let's advertise this usage by prioritizing its placement.

Signed-off-by: default avatarHuichun Feng <foxhoundsk.tw@gmail.com>
Link: https://lore.kernel.org/r/20240609173728.2950808-1-foxhoundsk.tw@gmail.com


Signed-off-by: default avatarBartosz Golaszewski <bartosz.golaszewski@linaro.org>
parent 54a687cd

Documentation/userspace-api/gpio/sysfs.rst

+4 −3
Original line number Diff line number Diff line
@@ -97,9 +97,10 @@ and have the following read/write attributes: 
		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.

		poll(2) returns, use pread(2) to read the value at offset

		zero. Alternatively, 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