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-rw-r--r--Documentation/gpio.txt15
1 files changed, 15 insertions, 0 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index e4e7daed2ba8..1866c27eec69 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -531,6 +531,13 @@ and have the following read/write attributes:
This file exists only if the pin can be configured as an
interrupt generating input pin.
+ "active_low" ... reads as either 0 (false) or 1 (true). Write
+ any nonzero value to invert the value attribute both
+ for reading and writing. Existing and subsequent
+ poll(2) support configuration via the edge attribute
+ for "rising" and "falling" edges will follow this
+ setting.
+
GPIO controllers have paths like /sys/class/gpio/gpiochip42/ (for the
controller implementing GPIOs starting at #42) and have the following
read-only attributes:
@@ -566,6 +573,8 @@ requested using gpio_request():
int gpio_export_link(struct device *dev, const char *name,
unsigned gpio)
+ /* change the polarity of a GPIO node in sysfs */
+ int gpio_sysfs_set_active_low(unsigned gpio, int value);
After a kernel driver requests a GPIO, it may only be made available in
the sysfs interface by gpio_export(). The driver can control whether the
@@ -580,3 +589,9 @@ After the GPIO has been exported, gpio_export_link() allows creating
symlinks from elsewhere in sysfs to the GPIO sysfs node. Drivers can
use this to provide the interface under their own device in sysfs with
a descriptive name.
+
+Drivers can use gpio_sysfs_set_active_low() to hide GPIO line polarity
+differences between boards from user space. This only affects the
+sysfs interface. Polarity change can be done both before and after
+gpio_export(), and previously enabled poll(2) support for either
+rising or falling edge will be reconfigured to follow this setting.