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| -rw-r--r-- | Documentation/leds/uleds.rst | 37 |
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diff --git a/Documentation/leds/uleds.rst b/Documentation/leds/uleds.rst new file mode 100644 index 000000000..832210980 --- /dev/null +++ b/Documentation/leds/uleds.rst @@ -0,0 +1,37 @@ +============== +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. |