diff options
Diffstat (limited to 'Documentation/gpio.txt')
| -rw-r--r-- | Documentation/gpio.txt | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 576ce463cf44..989f1130f4f3 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -105,12 +105,15 @@ setting up a platform_device using the GPIO, is mark its direction: /* set as input or output, returning 0 or negative errno */ int gpio_direction_input(unsigned gpio); - int gpio_direction_output(unsigned gpio); + int gpio_direction_output(unsigned gpio, int value); The return value is zero for success, else a negative errno. It should be checked, since the get/set calls don't have error returns and since misconfiguration is possible. (These calls could sleep.) +For output GPIOs, the value provided becomes the initial output value. +This helps avoid signal glitching during system startup. + Setting the direction can fail if the GPIO number is invalid, or when that particular GPIO can't be used in that mode. It's generally a bad idea to rely on boot firmware to have set the direction correctly, since |