From: Huichun Feng <foxhoundsk.tw@gmail.com>
To: Linus Walleij <linus.walleij@linaro.org>,
Bartosz Golaszewski <brgl@bgdev.pl>,
Jonathan Corbet <corbet@lwn.net>,
Kent Gibson <warthog618@gmail.com>,
linux-gpio@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: foxhoundsk.tw@gmail.com
Subject: [PATCH] docs: gpio: prefer pread(2) for interrupt reading
Date: Tue, 14 May 2024 12:12:23 +0800 [thread overview]
Message-ID: <20240514041223.800811-1-foxhoundsk.tw@gmail.com> (raw)
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(-)
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
next reply other threads:[~2024-05-14 4:12 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-14 4:12 Huichun Feng [this message]
2024-05-14 5:26 ` [PATCH] docs: gpio: prefer pread(2) for interrupt reading Bagas Sanjaya
2024-05-27 7:05 ` Huichun Feng
2024-05-27 7:34 ` Bartosz Golaszewski
2024-05-27 14:54 ` Bartosz Golaszewski
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