| David Lechner | e381322 | 2016-09-16 14:16:48 -0500 | [diff] [blame] | 1 | Userspace LEDs |
| 2 | ============== |
| 3 | |
| 4 | The uleds driver supports userspace LEDs. This can be useful for testing |
| 5 | triggers and can also be used to implement virtual LEDs. |
| 6 | |
| 7 | |
| 8 | Usage |
| 9 | ===== |
| 10 | |
| 11 | When the driver is loaded, a character device is created at /dev/uleds. To |
| 12 | create a new LED class device, open /dev/uleds and write a uleds_user_dev |
| 13 | structure to it (found in kernel public header file linux/uleds.h). |
| 14 | |
| 15 | #define LED_MAX_NAME_SIZE 64 |
| 16 | |
| 17 | struct uleds_user_dev { |
| 18 | char name[LED_MAX_NAME_SIZE]; |
| 19 | }; |
| 20 | |
| 21 | A new LED class device will be created with the name given. The name can be |
| 22 | any valid sysfs device node name, but consider using the LED class naming |
| 23 | convention of "devicename:color:function". |
| 24 | |
| 25 | The current brightness is found by reading a single byte from the character |
| 26 | device. Values are unsigned: 0 to 255. Reading will block until the brightness |
| 27 | changes. The device node can also be polled to notify when the brightness value |
| 28 | changes. |
| 29 | |
| 30 | The LED class device will be removed when the open file handle to /dev/uleds |
| 31 | is closed. |
| 32 | |
| 33 | Multiple LED class devices are created by opening additional file handles to |
| 34 | /dev/uleds. |
| 35 | |
| 36 | See tools/leds/uledmon.c for an example userspace program. |