Kindly ping. Sorry that the last ping wasn't sent in plain text. Huichun Feng <foxhoundsk.tw@xxxxxxxxx> 於 2024年5月14日 週二 下午12:12寫道： > > 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@xxxxxxxxx> > --- > 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 >
