Hi! > >>>The LED you are talking about _has_ a trigger, implemented in > >>>hardware. That trigger can change LED brightness behind kernel's (and > >>>userspace's) back. Don't pretend the trigger does not exist, it does. > >>> > >>>And when you do that, you'll have nice place to report changes to > >>>userspace -- trigger can now export that information, and offer poll() > >>>interface. > >> > >>Well, that sounds interesting. It is logically justifiable. > > > >Thanks. > > > >>I initially proposed exactly this solution, with recently > >>added userspace LED being a trigger listener. It seems a bit > >>awkward though. How would you listen to the trigger events? > > > >Trigger exposes a file in sysfs, with poll() working on that file > > Hmm, a new file would give the advantage of making it easy for > userspace to see if the trigger is poll-able, this is likely > better then my own proposal I just send. Good. > >(and > >probably read exposing the current brightness). > > If we do this, can we please make it mirror brightness, iow > also make it writable, that will make it easier for userspace > to deal with it. We can simply re-use the existing show / store > methods for brightness for this. Actually, echo 0 > brightness disables the trigger, IIRC. I'd avoid that here, you want to be able to turn off the backlight but still keep the trigger (and be notified of future changes). > I suggest we call it: > > trigger_brightness > > And only register it when a poll-able trigger is present. I'd call it 'current_brightness', but that's no big deal. Yes, only registering it for poll-able triggers makes sense. > >Key difference is that only triggers where this makes sense (keyboard > >backlight) expose it and carry the overhead. CPU trigger would > >definitely not do this. > > Ack only having some triggers pollable is important. Thanks, Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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