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authorDavid Lechner <david@lechnology.com>2016-09-16 14:16:48 -0500
committerJacek Anaszewski <j.anaszewski@samsung.com>2016-11-22 12:07:02 +0100
commite381322b0190c1253d347de3f28b5c37756fb651 (patch)
tree792a2bc1695cae581e152565e95127405424f5c6 /Documentation/leds
parent1001354ca34179f3db924eb66672442a173147dc (diff)
downloadblackbird-op-linux-e381322b0190c1253d347de3f28b5c37756fb651.tar.gz
blackbird-op-linux-e381322b0190c1253d347de3f28b5c37756fb651.zip
leds: Introduce userspace LED class driver
This driver creates a userspace leds driver similar to uinput. New LEDs are created by opening /dev/uleds and writing a uleds_user_dev struct. A new LED class device is registered with the name given in the struct. Reading will return a single byte that is the current brightness. The poll() syscall is also supported. It will be triggered whenever the brightness changes. Closing the file handle to /dev/uleds will remove the leds class device. Signed-off-by: David Lechner <david@lechnology.com> Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
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+Userspace LEDs
+==============
+
+The uleds driver supports userspace LEDs. This can be useful for testing
+triggers and can also be used to implement virtual LEDs.
+
+
+Usage
+=====
+
+When the driver is loaded, a character device is created at /dev/uleds. To
+create a new LED class device, open /dev/uleds and write a uleds_user_dev
+structure to it (found in kernel public header file linux/uleds.h).
+
+ #define LED_MAX_NAME_SIZE 64
+
+ struct uleds_user_dev {
+ char name[LED_MAX_NAME_SIZE];
+ };
+
+A new LED class device will be created with the name given. The name can be
+any valid sysfs device node name, but consider using the LED class naming
+convention of "devicename:color:function".
+
+The current brightness is found by reading a single byte from the character
+device. Values are unsigned: 0 to 255. Reading will block until the brightness
+changes. The device node can also be polled to notify when the brightness value
+changes.
+
+The LED class device will be removed when the open file handle to /dev/uleds
+is closed.
+
+Multiple LED class devices are created by opening additional file handles to
+/dev/uleds.
+
+See tools/leds/uledmon.c for an example userspace program.
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