From e381322b0190c1253d347de3f28b5c37756fb651 Mon Sep 17 00:00:00 2001 From: David Lechner Date: Fri, 16 Sep 2016 14:16:48 -0500 Subject: 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 Signed-off-by: Jacek Anaszewski --- Documentation/leds/uleds.txt | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) create mode 100644 Documentation/leds/uleds.txt (limited to 'Documentation/leds/uleds.txt') diff --git a/Documentation/leds/uleds.txt b/Documentation/leds/uleds.txt new file mode 100644 index 000000000000..13e375a580f9 --- /dev/null +++ b/Documentation/leds/uleds.txt @@ -0,0 +1,36 @@ +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. -- cgit v1.2.3