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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