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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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22
Documentation/gpio.txt
View File

@ -109,17 +109,19 @@ 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:
test if such number from such a structure 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.
example, a number might be valid but temporarily unused on a given board.
Whether a platform supports multiple GPIO controllers is a platform-specific
implementation issue, as are whether that support can leave "holes" in the space
of GPIO numbers, and whether new controllers can be added at runtime. Such issues
can affect things including whether adjacent GPIO numbers are both valid.
Using GPIOs
-----------
@ -480,12 +482,16 @@ To support this framework, a platform's Kconfig will "select" either
ARCH_REQUIRE_GPIOLIB or ARCH_WANT_OPTIONAL_GPIOLIB
and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines
three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep().
They may also want to provide a custom value for ARCH_NR_GPIOS.
ARCH_REQUIRE_GPIOLIB means that the gpio-lib code will always get compiled
It may also provide a custom value for ARCH_NR_GPIOS, so that it better
reflects the number of GPIOs in actual use on that platform, without
wasting static table space. (It should count both built-in/SoC GPIOs and
also ones on GPIO expanders.
ARCH_REQUIRE_GPIOLIB means that the gpiolib code will always get compiled
into the kernel on that architecture.
ARCH_WANT_OPTIONAL_GPIOLIB means the gpio-lib code defaults to off and the user
ARCH_WANT_OPTIONAL_GPIOLIB means the gpiolib code defaults to off and the user
can enable it and build it into the kernel optionally.
If neither of these options are selected, the platform does not support

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;
}