diff options
Diffstat (limited to 'Documentation')
| -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: | |||
| 105 | 105 | ||
| 106 | /* set as input or output, returning 0 or negative errno */ | 106 | /* set as input or output, returning 0 or negative errno */ |
| 107 | int gpio_direction_input(unsigned gpio); | 107 | int gpio_direction_input(unsigned gpio); |
| 108 | int gpio_direction_output(unsigned gpio); | 108 | int gpio_direction_output(unsigned gpio, int value); |
| 109 | 109 | ||
| 110 | The return value is zero for success, else a negative errno. It should | 110 | The return value is zero for success, else a negative errno. It should |
| 111 | be checked, since the get/set calls don't have error returns and since | 111 | be checked, since the get/set calls don't have error returns and since |
| 112 | misconfiguration is possible. (These calls could sleep.) | 112 | misconfiguration is possible. (These calls could sleep.) |
| 113 | 113 | ||
| 114 | For output GPIOs, the value provided becomes the initial output value. | ||
| 115 | This helps avoid signal glitching during system startup. | ||
| 116 | |||
| 114 | Setting the direction can fail if the GPIO number is invalid, or when | 117 | Setting the direction can fail if the GPIO number is invalid, or when |
| 115 | that particular GPIO can't be used in that mode. It's generally a bad | 118 | that particular GPIO can't be used in that mode. It's generally a bad |
| 116 | idea to rely on boot firmware to have set the direction correctly, since | 119 | idea to rely on boot firmware to have set the direction correctly, since |