From ebde7b062cd9e2ea968c93f23f73dd28c0a192d1 Mon Sep 17 00:00:00 2001 From: Bernhard Walle <walle@corscience.de> Date: Thu, 18 Nov 2010 12:27:33 -0800 Subject: [PATCH] Documentation/gpio.txt: explain poll/select usage Add a bit more information how to use poll(2) on GPIO value files correctly. For me it was not clear that I need to poll(2) for POLLPRI|POLLERR or select(2) for exceptfds. Signed-off-by: Bernhard Walle <walle@corscience.de> Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> --- Documentation/gpio.txt | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 9633da01ff46a..792faa3c06cf7 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -617,6 +617,16 @@ and have the following read/write attributes: is configured as an output, this value may be written; any nonzero value is treated as high. + If the pin can be configured as interrupt-generating interrupt + and if it has been configured to generate interrupts (see the + description of "edge"), you can poll(2) on that file and + 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. + "edge" ... reads as either "none", "rising", "falling", or "both". Write these strings to select the signal edge(s) that will make poll(2) on the "value" file return. -- GitLab