X-Git-Url: http://pilppa.org/gitweb/gitweb.cgi?a=blobdiff_plain;f=Documentation%2Fgpio.txt;h=c35ca9e40d4ca8ae0cbf7c06c639d8531ae8d9dd;hb=5f828546e1acb45678e73d3a9a796c1a3a8c7846;hp=54630095aa3c8f841c097e723eef518f660a30a7;hpb=6f58d79598c184dc4f18ceddfaa5fa7483bce0a5;p=linux-2.6-omap-h63xx.git

diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index 54630095aa3..c35ca9e40d4 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -107,6 +107,16 @@ type of GPIO controller, and on one particular board 80-95 with an FPGA.
 The numbers need not be contiguous; either of those platforms could also
 use numbers 2000-2063 to identify GPIOs in a bank of I2C GPIO expanders.
 
+If you want to initialize a structure with an invalid GPIO number, use
+some negative number (perhaps "-EINVAL"); that will never be valid.  To
+test if a number could reference a GPIO, you may use this predicate:
+
+	int gpio_is_valid(int number);
+
+A number that's not valid will be rejected by calls which may request
+or free GPIOs (see below).  Other numbers may also be rejected; for
+example, a number might be valid but unused on a given board.
+
 Whether a platform supports multiple GPIO controllers is currently a
 platform-specific implementation issue.