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| author | Bernhard Walle <walle@corscience.de> | 2010-11-18 12:27:33 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2010-11-18 15:00:46 -0800 |
| commit | ebde7b062cd9e2ea968c93f23f73dd28c0a192d1 (patch) | |
| tree | 143d247e7d9c3e505961d769494bd267c14c5078 /Documentation/gpio.txt | |
| parent | 09c9feb94672bdb3ca6d424a292ffc26eff8ca0b (diff) | |
| download | lwn-ebde7b062cd9e2ea968c93f23f73dd28c0a192d1.tar.gz lwn-ebde7b062cd9e2ea968c93f23f73dd28c0a192d1.zip | |
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>
Diffstat (limited to 'Documentation/gpio.txt')
| -rw-r--r-- | Documentation/gpio.txt | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 9633da01ff46..792faa3c06cf 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. |