path: root/Documentation/leds
diff options
authorTony Makkiel <>2016-05-18 17:22:45 +0100
committerJacek Anaszewski <>2016-06-08 11:47:06 +0200
commit7cfe749fad5158247282f2fee30773fd454029ab (patch)
tree0d3ad9db7f04c077e7ce80daf10be1de4477fc80 /Documentation/leds
parentaf8c34ce6ae32addda3788d54a7e340cad22516b (diff)
leds: core: Fix brightness setting upon hardware blinking enabled
Commit 76931edd54f8 ("leds: fix brightness changing when software blinking is active") changed the semantics of led_set_brightness() which according to the documentation should disable blinking upon any brightness setting. Moreover it made it different for soft blink case, where it was possible to change blink brightness, and for hardware blink case, where setting any brightness greater than 0 was ignored. While the change itself is against the documentation claims, it was driven also by the fact that timer trigger remained active after turning blinking off. Fixing that would have required major refactoring in the led-core, led-class, and led-triggers because of cyclic dependencies. Finally, it has been decided that allowing for brightness change during blinking is beneficial as it can be accomplished without disturbing blink rhythm. The change in brightness setting semantics will not affect existing LED class drivers that implement blink_set op thanks to the LED_BLINK_SW flag introduced by this patch. The flag state will be from now on checked in led_set_brightness() which will allow to distinguish between software and hardware blink mode. In the latter case the control will be passed directly to the drivers which apply their semantics on brightness set, which is disable the blinking in case of most such drivers. New drivers will apply new semantics and just change the brightness while hardware blinking is on, if possible. The issue was smuggled by subsequent LED core improvements, which modified the code that originally introduced the problem. Fixes: f1e80c07416a ("leds: core: Add two new LED_BLINK_ flags") Signed-off-by: Tony Makkiel <> Signed-off-by: Jacek Anaszewski <>
Diffstat (limited to 'Documentation/leds')
1 files changed, 2 insertions, 2 deletions
diff --git a/Documentation/leds/leds-class.txt b/Documentation/leds/leds-class.txt
index d406d98339b2..44f5e6bccd97 100644
--- a/Documentation/leds/leds-class.txt
+++ b/Documentation/leds/leds-class.txt
@@ -74,8 +74,8 @@ blink_set() function (see <linux/leds.h>). To set an LED to blinking,
however, it is better to use the API function led_blink_set(), as it
will check and implement software fallback if necessary.
-To turn off blinking again, use the API function led_brightness_set()
-as that will not just set the LED brightness but also stop any software
+To turn off blinking, use the API function led_brightness_set()
+with brightness value LED_OFF, which should stop any software
timers that may have been required for blinking.
The blink_set() function should choose a user friendly blinking value