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-rw-r--r--Documentation/gpio.txt5
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
110The return value is zero for success, else a negative errno. It should 110The return value is zero for success, else a negative errno. It should
111be checked, since the get/set calls don't have error returns and since 111be checked, since the get/set calls don't have error returns and since
112misconfiguration is possible. (These calls could sleep.) 112misconfiguration is possible. (These calls could sleep.)
113 113
114For output GPIOs, the value provided becomes the initial output value.
115This helps avoid signal glitching during system startup.
116
114Setting the direction can fail if the GPIO number is invalid, or when 117Setting the direction can fail if the GPIO number is invalid, or when
115that particular GPIO can't be used in that mode. It's generally a bad 118that particular GPIO can't be used in that mode. It's generally a bad
116idea to rely on boot firmware to have set the direction correctly, since 119idea to rely on boot firmware to have set the direction correctly, since