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-rw-r--r--Documentation/gpio.txt12
1 files changed, 11 insertions, 1 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index 8b69811a9642..18022e249c53 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -389,11 +389,21 @@ either NULL or the label associated with that GPIO when it was requested.
389 389
390Platform Support 390Platform Support
391---------------- 391----------------
392To support this framework, a platform's Kconfig will "select HAVE_GPIO_LIB" 392To support this framework, a platform's Kconfig will "select" either
393ARCH_REQUIRE_GPIOLIB or ARCH_WANT_OPTIONAL_GPIOLIB
393and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines 394and arrange that its <asm/gpio.h> includes <asm-generic/gpio.h> and defines
394three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep(). 395three functions: gpio_get_value(), gpio_set_value(), and gpio_cansleep().
395They may also want to provide a custom value for ARCH_NR_GPIOS. 396They may also want to provide a custom value for ARCH_NR_GPIOS.
396 397
398ARCH_REQUIRE_GPIOLIB means that the gpio-lib code will always get compiled
399into the kernel on that architecture.
400
401ARCH_WANT_OPTIONAL_GPIOLIB means the gpio-lib code defaults to off and the user
402can enable it and build it into the kernel optionally.
403
404If neither of these options are selected, the platform does not support
405GPIOs through GPIO-lib and the code cannot be enabled by the user.
406
397Trivial implementations of those functions can directly use framework 407Trivial implementations of those functions can directly use framework
398code, which always dispatches through the gpio_chip: 408code, which always dispatches through the gpio_chip:
399 409