| Message ID | 20240609173728.2950808-1-foxhoundsk.tw@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] docs: gpio: prefer pread(2) for interrupt reading | expand |
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> On Mon, 10 Jun 2024 01:37:28 +0800, Huichun Feng wrote: > 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. > > [...] Applied, thanks! [1/1] docs: gpio: prefer pread(2) for interrupt reading commit: 7f1e45f4ae7671550e15354ef87194bccd99ecec Best regards,
diff --git a/Documentation/userspace-api/gpio/sysfs.rst b/Documentation/userspace-api/gpio/sysfs.rst index 116921048..bd64896de 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
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> --- Changes in v2: - rebase against the latest tree. v1 link: https://lore.kernel.org/linux-gpio/20240514041223.800811-1-foxhoundsk.tw@gmail.com/T/#mfa19d877e6056936d3a2025cb64ca8c5b8718644 --- Documentation/userspace-api/gpio/sysfs.rst | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)