X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=Documentation%2Fleds-class.txt;h=8fd5ca2ae32dde4d9eb27722942a5d099f4afbc3;hb=b75396a4ea473a2cd4f2fb99a81b2289265a8021;hp=8c35c0426110f149100be9cb2c17921e8e25ae39;hpb=75c1d31d9ea71025b73430c696b727e8aa15872d;p=safe%2Fjmp%2Flinux-2.6 diff --git a/Documentation/leds-class.txt b/Documentation/leds-class.txt index 8c35c04..8fd5ca2 100644 --- a/Documentation/leds-class.txt +++ b/Documentation/leds-class.txt @@ -1,3 +1,4 @@ + LED handling under Linux ======================== @@ -5,10 +6,10 @@ If you're reading this and thinking about keyboard leds, these are handled by the input subsystem and the led class is *not* needed. In its simplest form, the LED class just allows control of LEDs from -userspace. LEDs appear in /sys/class/leds/. The brightness file will -set the brightness of the LED (taking a value 0-255). Most LEDs don't -have hardware brightness support so will just be turned on for non-zero -brightness settings. +userspace. LEDs appear in /sys/class/leds/. The maximum brightness of the +LED is defined in max_brightness file. The brightness file will set the brightness +of the LED (taking a value 0-max_brightness). Most LEDs don't have hardware +brightness support so will just be turned on for non-zero brightness settings. The class also introduces the optional concept of an LED trigger. A trigger is a kernel based source of led events. Triggers can either be simple or @@ -19,6 +20,12 @@ optimises away. Complex triggers whilst available to all LEDs have LED specific parameters and work on a per LED basis. The timer trigger is an example. +The timer trigger will periodically change the LED brightness between +LED_OFF and the current brightness setting. The "on" and "off" time can +be specified via /sys/class/leds//delay_{on,off} in milliseconds. +You can change the brightness value of a LED independently of the timer +trigger. However, if you set the brightness value to LED_OFF it will +also disable the timer trigger. You can change triggers in a similar manner to the way an IO scheduler is chosen (via /sys/class/leds//trigger). Trigger specific @@ -39,12 +46,33 @@ LED Device Naming Is currently of the form: -"devicename:colour" +"devicename:colour:function" There have been calls for LED properties such as colour to be exported as individual led class attributes. As a solution which doesn't incur as much overhead, I suggest these become part of the device name. The naming scheme -above leaves scope for further attributes should they be needed. +above leaves scope for further attributes should they be needed. If sections +of the name don't apply, just leave that section blank. + + +Hardware accelerated blink of LEDs +================================== + +Some LEDs can be programmed to blink without any CPU interaction. To +support this feature, a LED driver can optionally implement the +blink_set() function (see ). If implemented, triggers can +attempt to use it before falling back to software timers. The blink_set() +function should return 0 if the blink setting is supported, or -EINVAL +otherwise, which means that LED blinking will be handled by software. + +The blink_set() function should choose a user friendly blinking +value if it is called with *delay_on==0 && *delay_off==0 parameters. In +this case the driver should give back the chosen value through delay_on +and delay_off parameters to the leds subsystem. + +Setting the brightness to zero with brightness_set() callback function +should completely turn off the LED and cancel the previously programmed +hardware blinking function, if any. Known Issues @@ -55,10 +83,6 @@ 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, this should be exported as a device specific sysfs -attribute rather than part of the class if this functionality is required. - Future Development ==================