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Diffstat (limited to 'Documentation/gpio.txt')
| -rw-r--r-- | Documentation/gpio.txt | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 1866c27eec6..c2c6e9b39bb 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -253,6 +253,70 @@ pin setup (e.g. controlling which pin the GPIO uses, pullup/pulldown). Also note that it's your responsibility to have stopped using a GPIO before you free it. +Considering in most cases GPIOs are actually configured right after they +are claimed, three additional calls are defined: + + /* request a single GPIO, with initial configuration specified by + * 'flags', identical to gpio_request() wrt other arguments and + * return value + */ + int gpio_request_one(unsigned gpio, unsigned long flags, const char *label); + + /* request multiple GPIOs in a single call + */ + int gpio_request_array(struct gpio *array, size_t num); + + /* release multiple GPIOs in a single call + */ + void gpio_free_array(struct gpio *array, size_t num); + +where 'flags' is currently defined to specify the following properties: + + * GPIOF_DIR_IN - to configure direction as input + * GPIOF_DIR_OUT - to configure direction as output + + * GPIOF_INIT_LOW - as output, set initial level to LOW + * GPIOF_INIT_HIGH - as output, set initial level to HIGH + +since GPIOF_INIT_* are only valid when configured as output, so group valid +combinations as: + + * GPIOF_IN - configure as input + * GPIOF_OUT_INIT_LOW - configured as output, initial level LOW + * GPIOF_OUT_INIT_HIGH - configured as output, initial level HIGH + +In the future, these flags can be extended to support more properties such +as open-drain status. + +Further more, to ease the claim/release of multiple GPIOs, 'struct gpio' is +introduced to encapsulate all three fields as: + + struct gpio { + unsigned gpio; + unsigned long flags; + const char *label; + }; + +A typical example of usage: + + static struct gpio leds_gpios[] = { + { 32, GPIOF_OUT_INIT_HIGH, "Power LED" }, /* default to ON */ + { 33, GPIOF_OUT_INIT_LOW, "Green LED" }, /* default to OFF */ + { 34, GPIOF_OUT_INIT_LOW, "Red LED" }, /* default to OFF */ + { 35, GPIOF_OUT_INIT_LOW, "Blue LED" }, /* default to OFF */ + { ... }, + }; + + err = gpio_request_one(31, GPIOF_IN, "Reset Button"); + if (err) + ... + + err = gpio_request_array(leds_gpios, ARRAY_SIZE(leds_gpios)); + if (err) + ... + + gpio_free_array(leds_gpios, ARRAY_SIZE(leds_gpios)); + GPIOs mapped to IRQs -------------------- |