make the conversion to the LED subsystem (or assist with it) if appropriate. Implementation Details ====================== I've stripped a lot of code out of John's original LED class. Colours were removed as LED colour is now part of the device name. Multiple colours are to be handled as multiple led devices. This means you get full control over each colour. I also removed the LED hardware timer code as the generic timer isn't going to add much overhead and is just as useful. I also decided to have the LED core track the current LED status (to ease suspend/resume handling) removing the need for brightness_get implementations in the LED drivers. An underlying design philosophy is simplicity. The aim is to keep a small amount of code giving as much functionality as possible. The major new idea is the led "trigger". A trigger is a source of led events. Triggers can either be simple or complex. A simple trigger isn't configurable and is designed to slot into existing subsystems with minimal additional code. Examples are the ide-disk, nand-disk and zaurus-charging triggers. With leds disabled, the code optimises away. Examples are nand-disk and ide-disk. Complex triggers whilst available to all LEDs have LED specific parameters and work on a per LED basis. The timer trigger is an example. You can change triggers in a similar manner to the way an IO scheduler is chosen (via /sys/class/leds/somedevice/trigger). So far there are only a handful of examples but it should easy to add further LED triggers without too much interference into other subsystems. Known Issues ============ The LED Trigger core cannot be a module as the simple trigger functions would cause nightmare dependency issues. I see this as a minor issue compared to the benefits the simple trigger functionality brings. The rest of the LED subsystem can be modular. Some leds can be programmed to flash in hardware. As this isn't a generic LED device property, I think this should be exported as a device specific sysfs attribute rather than part of the class if this functionality is required (eg. to keep the led flashing whilst the device is suspended). Future Development ================== At the moment, a trigger can't be created specifically for a single LED. There are a number of cases where a trigger might only be mappable to a particular LED. The addition of triggers provided by the LED driver should cover this option and be possible to add without breaking the current interface. A CPU activity trigger similar to that found in the arm led implementation should be trivial to add. This patch: Add some brief documentation of the design decisions behind the LED class and how it appears to users. Signed-off-by: Richard Purdie Cc: Russell King Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Äê¼