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e381322b DL |
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. |