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-rw-r--r--Documentation/gpio.txt22
-rw-r--r--include/asm-generic/gpio.h14
2 files changed, 27 insertions, 9 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index d96a6dba5748..9633da01ff46 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -109,17 +109,19 @@ use numbers 2000-2063 to identify GPIOs in a bank of I2C GPIO expanders.
109 109
110If you want to initialize a structure with an invalid GPIO number, use 110If you want to initialize a structure with an invalid GPIO number, use
111some negative number (perhaps "-EINVAL"); that will never be valid. To 111some negative number (perhaps "-EINVAL"); that will never be valid. To
112test if a number could reference a GPIO, you may use this predicate: 112test if such number from such a structure could reference a GPIO, you
113may use this predicate:
113 114
114 int gpio_is_valid(int number); 115 int gpio_is_valid(int number);
115 116
116A number that's not valid will be rejected by calls which may request 117A number that's not valid will be rejected by calls which may request
117or free GPIOs (see below). Other numbers may also be rejected; for 118or free GPIOs (see below). Other numbers may also be rejected; for
118example, a number might be valid but unused on a given board. 119example, a number might be valid but temporarily unused on a given board.
119
120Whether a platform supports multiple GPIO controllers is currently a
121platform-specific implementation issue.
122 120
121Whether a platform supports multiple GPIO controllers is a platform-specific
122implementation issue, as are whether that support can leave "holes" in the space
123of GPIO numbers, and whether new controllers can be added at runtime. Such issues
124can affect things including whether adjacent GPIO numbers are both valid.
123 125
124Using GPIOs 126Using GPIOs
125----------- 127-----------
@@ -480,12 +482,16 @@ To support this framework, a platform's Kconfig will "select" either
480ARCH_REQUIRE_GPIOLIB or ARCH_WANT_OPTIONAL_GPIOLIB 482ARCH_REQUIRE_GPIOLIB or ARCH_WANT_OPTIONAL_GPIOLIB
481and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines 483and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines
482three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep(). 484three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep().
483They may also want to provide a custom value for ARCH_NR_GPIOS.
484 485
485ARCH_REQUIRE_GPIOLIB means that the gpio-lib code will always get compiled 486It may also provide a custom value for ARCH_NR_GPIOS, so that it better
487reflects the number of GPIOs in actual use on that platform, without
488wasting static table space. (It should count both built-in/SoC GPIOs and
489also ones on GPIO expanders.
490
491ARCH_REQUIRE_GPIOLIB means that the gpiolib code will always get compiled
486into the kernel on that architecture. 492into the kernel on that architecture.
487 493
488ARCH_WANT_OPTIONAL_GPIOLIB means the gpio-lib code defaults to off and the user 494ARCH_WANT_OPTIONAL_GPIOLIB means the gpiolib code defaults to off and the user
489can enable it and build it into the kernel optionally. 495can enable it and build it into the kernel optionally.
490 496
491If neither of these options are selected, the platform does not support 497If neither of these options are selected, the platform does not support
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index c7376bf80b06..8ca18e26d7e3 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -16,15 +16,27 @@
16 * While the GPIO programming interface defines valid GPIO numbers 16 * While the GPIO programming interface defines valid GPIO numbers
17 * to be in the range 0..MAX_INT, this library restricts them to the 17 * to be in the range 0..MAX_INT, this library restricts them to the
18 * smaller range 0..ARCH_NR_GPIOS-1. 18 * smaller range 0..ARCH_NR_GPIOS-1.
19 *
20 * ARCH_NR_GPIOS is somewhat arbitrary; it usually reflects the sum of
21 * builtin/SoC GPIOs plus a number of GPIOs on expanders; the latter is
22 * actually an estimate of a board-specific value.
19 */ 23 */
20 24
21#ifndef ARCH_NR_GPIOS 25#ifndef ARCH_NR_GPIOS
22#define ARCH_NR_GPIOS 256 26#define ARCH_NR_GPIOS 256
23#endif 27#endif
24 28
29/*
30 * "valid" GPIO numbers are nonnegative and may be passed to
31 * setup routines like gpio_request(). only some valid numbers
32 * can successfully be requested and used.
33 *
34 * Invalid GPIO numbers are useful for indicating no-such-GPIO in
35 * platform data and other tables.
36 */
37
25static inline int gpio_is_valid(int number) 38static inline int gpio_is_valid(int number)
26{ 39{
27 /* only some non-negative numbers are valid */
28 return ((unsigned)number) < ARCH_NR_GPIOS; 40 return ((unsigned)number) < ARCH_NR_GPIOS;
29} 41}
30 42