leds: Introduce userspace LED class driver

[sfrench/cifs-2.6.git] / Documentation / leds / uleds.txt

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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.