[PATCH] Documentation: gpio: Clarify usage of poll(2)

[Bernhard Walle <walle@corscience.de>]

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>
---
 Documentation/gpio.txt |   10 ++++++++++
 1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index 9633da0..792faa3 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.
-- 
1.7.1