Re: Bug when using both "set" and "blink" functions

[Pavel Machek <pavel@ucw.cz>]

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On Wed 2017-11-22 00:55:12, Craig McQueen wrote:
> I'd like to control a LED to possibly be any of:
> 
> * Off
> * On
> * Blinking
> 
> I've had this working fine in 3.14.x kernel.
> 
> But when upgrading to 4.4.x, I found that the transition from "blinking" to "on" didn't work. Namely, if it's blinking and then I call led_set_brightness(led_cdev, LED_FULL), then it wouldn't work (I can't remember if it turned off, or remained blinking; it wasn't on anyway). I worked around it by calling led_set_brightness(led_cdev, LED_OFF) just before led_set_brightness(led_cdev, LED_FULL).
> 
> Now I have upgraded to 4.9.x, and found that the transition from "blinking" to "on" again isn't working. The LED ends up being off instead of on.
> 
> Examining the code of led_set_brightness():
> 
> * Behaviour is different depending on whether the brightness is LED_OFF (it schedules the blink to be turned off "soon") or other (it alters the brightness of subsequent blinks).
> * It looks as though there are race conditions in the transition from blinking to steady off -- it schedules the blink to be turned off "soon", so it's difficult to guarantee a reliable transition from blinking to on/off.
> 
> The combination of the above two points makes it seem difficult to robustly go from blinking to off/on.
> 
> So, my questions are:
> 
> * What is the correct way to use the API to reliably control an LED
> for a combination of off/on/blinking?

You should be able to use sysfs from the userland. .. if that is
broken we need to fix it.

What are you trying to do?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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