| Message ID | 20240602074925.2489486-1-foxhoundsk.tw@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | docs: gpio: prefer pread(2) for interrupt reading | expand |
On Sun, Jun 2, 2024 at 9:49 AM Huichun Feng <foxhoundsk.tw@gmail.com> 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. > > Signed-off-by: Huichun Feng <foxhoundsk.tw@gmail.com> > --- > 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 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 > -- > 2.34.1 > Please don't send new versions of a patch as responses in an email thread. Otherwise tools such as b4 cannot tell if it's a new version or part of a larger series. Please always start a new thread with get send-email or - better yet - start using b4 and let it manage the series for you. Please resend this correctly. Bart
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> --- Documentation/userspace-api/gpio/sysfs.rst | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)