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authorMárton Németh <nm127@freemail.hu>2007-10-31 10:07:12 -0400
committerRichard Purdie <rpurdie@rpsys.net>2008-02-07 04:49:38 -0500
commit4c79141d28bc290ae307e3f81f5bc909c26faf6e (patch)
tree9c6dc51c441dfc1c84cc27ece43087515c06967c /Documentation
parent6c152beefbf90579d21afc4f7e075b1f801f9a75 (diff)
leds: Add support for hardware accelerated LED flashing
Extends the leds subsystem with a blink_set() callback function which can be optionally implemented by a LED driver. If implemented, the driver can use the hardware acceleration for blinking a LED. Signed-off-by: Márton Németh <nm127@freemail.hu> Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/leds-class.txt24
1 files changed, 20 insertions, 4 deletions
diff --git a/Documentation/leds-class.txt b/Documentation/leds-class.txt
index 877af6efc18b..56757c751d6f 100644
--- a/Documentation/leds-class.txt
+++ b/Documentation/leds-class.txt
@@ -48,6 +48,26 @@ above leaves scope for further attributes should they be needed. If sections
48of the name don't apply, just leave that section blank. 48of the name don't apply, just leave that section blank.
49 49
50 50
51Hardware accelerated blink of LEDs
52==================================
53
54Some LEDs can be programmed to blink without any CPU interaction. To
55support this feature, a LED driver can optionally implement the
56blink_set() function (see <linux/leds.h>). If implemeted, triggers can
57attempt to use it before falling back to software timers. The blink_set()
58function should return 0 if the blink setting is supported, or -EINVAL
59otherwise, which means that LED blinking will be handled by software.
60
61The blink_set() function should choose a user friendly blinking
62value if it is called with *delay_on==0 && *delay_off==0 parameters. In
63this case the driver should give back the chosen value through delay_on
64and delay_off parameters to the leds subsystem.
65
66Any call to the brightness_set() callback function should cancel the
67previously programmed hardware blinking function so setting the brightness
68to 0 can also cancel the blinking of the LED.
69
70
51Known Issues 71Known Issues
52============ 72============
53 73
@@ -56,10 +76,6 @@ would cause nightmare dependency issues. I see this as a minor issue
56compared to the benefits the simple trigger functionality brings. The 76compared to the benefits the simple trigger functionality brings. The
57rest of the LED subsystem can be modular. 77rest of the LED subsystem can be modular.
58 78
59Some leds can be programmed to flash in hardware. As this isn't a generic
60LED device property, this should be exported as a device specific sysfs
61attribute rather than part of the class if this functionality is required.
62
63 79
64Future Development 80Future Development
65================== 81==================