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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:
/* 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