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: Huichun Feng <foxhoundsk.tw@gmail.com>
Link: https://lore.kernel.org/r/20240609173728.2950808-1-foxhoundsk.tw@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

diff --git a/Documentation/userspace-api/gpio/sysfs.rst b/Documentation/userspace-api/gpio/sysfs.rst
index 116921048b18e92f4bb66c81492234c3ddc11589..bd64896de91a16eb1d47cb34affb093e9af858bd 100644 (file)
--- a/Documentation/userspace-api/gpio/sysfs.rst
+++ b/Documentation/userspace-api/gpio/sysfs.rst
@@ -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