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gpio: doc updates

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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>
This commit is contained in:
David Brownell
2010-09-09 16:38:03 -07:00
committed by Linus Torvalds
parent 5affb60772
commit c956126c13
2 changed files with 27 additions and 9 deletions
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14
include/asm-generic/gpio.h
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@ -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;
}