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Date: Tue, 14 May 2024 12:12:23 +0800 From: Huichun Feng <foxhoundsk.tw@...il.com> To: Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>, Jonathan Corbet <corbet@....net>, Kent Gibson <warthog618@...il.com>, linux-gpio@...r.kernel.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org Cc: foxhoundsk.tw@...il.com Subject: [PATCH] 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@...il.com> --- Documentation/driver-api/gpio/legacy.rst | 6 ++++-- Documentation/userspace-api/gpio/sysfs.rst | 7 ++++--- 2 files changed, 8 insertions(+), 5 deletions(-) diff --git a/Documentation/driver-api/gpio/legacy.rst b/Documentation/driver-api/gpio/legacy.rst index b6505914791c..c1a083444b0c 100644 --- a/Documentation/driver-api/gpio/legacy.rst +++ b/Documentation/driver-api/gpio/legacy.rst @@ -648,8 +648,10 @@ 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. 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. + 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 "both". Write these strings to select the signal edge(s) 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 -- 2.34.1
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