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authorDavid Brownell <dbrownell@users.sourceforge.net>2010-09-09 16:38:03 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-09-09 18:57:24 -0700
commitc956126c137d97acb6f4d56fa9572d0bcc84e4ed (patch)
treeaad2bdd087f9b5ea2abbf633b7f61ebd326ce562 /include/asm-generic
parent5affb607720d734ca572b8a77c5c7d62d3042b6f (diff)
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gpio: doc updates
There's been some recent confusion about error checking GPIO numbers. briefly, it should be handled mostly during setup, when gpio_request() is called, and NEVER by expectig gpio_is_valid to report more than never-usable GPIO numbers. [akpm@linux-foundation.org: terminate unterminated comment] Signed-off-by: David Brownell <dbrownell@users.sourceforge.net> Cc: Eric Miao" <eric.y.miao@gmail.com> Cc: "Ryan Mallon" <ryan@bluewatersys.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/asm-generic')
-rw-r--r--include/asm-generic/gpio.h14
1 files changed, 13 insertions, 1 deletions
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index c7376bf80b0..8ca18e26d7e 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -16,15 +16,27 @@
* While the GPIO programming interface defines valid GPIO numbers
* to be in the range 0..MAX_INT, this library restricts them to the
* smaller range 0..ARCH_NR_GPIOS-1.
+ *
+ * ARCH_NR_GPIOS is somewhat arbitrary; it usually reflects the sum of
+ * builtin/SoC GPIOs plus a number of GPIOs on expanders; the latter is
+ * actually an estimate of a board-specific value.
*/
#ifndef ARCH_NR_GPIOS
#define ARCH_NR_GPIOS 256
#endif
+/*
+ * "valid" GPIO numbers are nonnegative and may be passed to
+ * setup routines like gpio_request(). only some valid numbers
+ * can successfully be requested and used.
+ *
+ * Invalid GPIO numbers are useful for indicating no-such-GPIO in
+ * platform data and other tables.
+ */
+
static inline int gpio_is_valid(int number)
{
- /* only some non-negative numbers are valid */
return ((unsigned)number) < ARCH_NR_GPIOS;
}