diff mbox series

docs: gpio: prefer pread(2) for interrupt reading

Message ID 20240514041223.800811-1-foxhoundsk.tw@gmail.com
State Superseded
Headers show
Series docs: gpio: prefer pread(2) for interrupt reading | expand

Commit Message

Huichun Feng May 14, 2024, 4:12 a.m. UTC
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/driver-api/gpio/legacy.rst   | 6 ++++--
 Documentation/userspace-api/gpio/sysfs.rst | 7 ++++---
 2 files changed, 8 insertions(+), 5 deletions(-)

Comments

Bartosz Golaszewski May 27, 2024, 7:34 a.m. UTC | #1
On Mon, May 27, 2024 at 9:05 AM Huichun Feng <foxhoundsk.tw@gmail.com> wrote:
>
> Kindly ping.
>
> Sorry that the last ping wasn't sent in plain text.
>
>

Please don't ping me on the morning of the day after the merge window
closes. I don't pick up patches for the next release during the merge
window (like most maintainers) and I need some time to catch up on my
queue during rc1.

Bart
Bartosz Golaszewski May 27, 2024, 2:54 p.m. UTC | #2
On Tue, May 14, 2024 at 6:12 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>
> ---

This doesn't apply on top of gpio/for-next, please rebase and resend.

Bart
diff mbox series

Patch

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