1 files changed, 15 insertions, 0 deletions

diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index e4e7daed2ba..1866c27eec6 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.