From 7f1e45f4ae7671550e15354ef87194bccd99ecec Mon Sep 17 00:00:00 2001 From: Huichun Feng Date: Mon, 10 Jun 2024 01:37:28 +0800 Subject: 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 Link: https://lore.kernel.org/r/20240609173728.2950808-1-foxhoundsk.tw@gmail.com Signed-off-by: Bartosz Golaszewski --- Documentation/userspace-api/gpio/sysfs.rst | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/Documentation/userspace-api/gpio/sysfs.rst b/Documentation/userspace-api/gpio/sysfs.rst index 116921048b18..bd64896de91a 100644 --- 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 -- cgit