Messages in this thread | | | Subject | Re: LEDs that change brightness "itself" -- that's a trigger. Re: PM regression with LED changes in next-20161109 | From | Hans de Goede <> | Date | Tue, 15 Nov 2016 15:30:57 +0100 |
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Hi,
On 15-11-16 15:04, Jacek Anaszewski wrote: > On 11/15/2016 02:48 PM, Hans de Goede wrote: >> Hi, >> >> On 15-11-16 14:28, Jacek Anaszewski wrote: >>> On 11/15/2016 01:06 PM, Hans de Goede wrote: >>>> Hi, >>>> >>>> On 15-11-16 12:48, Pavel Machek wrote: >>>>> 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). >>>> >>>> True, that is easy to do the store method will just need to call >>>> led_set_brightness_nosleep instead of led_set_brightness, this >>>> will skip the checks to stop blinking in led_set_brightness and >>>> otherwise is equivalent. >>>> >>>>>> 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. >>>> >>>> current_brightness works for me. I will take a shot a patch-set >>>> implementing this. >>> >>> Word "current" is not precise here. >>> >>> It can be thought of as either last brightness set by the >>> user or the brightness currently written to the device >>> (returned by brightness file). >>> >>> There is a semantic discrepancy in our requirements - >>> we want the file representing both permanent brightness >>> set by the user and brightness set by the hardware. >>> >>> The two stand in contradiction to each other since >>> brightness set by the user can be adjusted by the hardware. >>> >>> Reading the file shouldn't update brightness property of >>> struct led_classdev, so it shouldn't call led_update_brightness() >>> but it still should allow reading brightness set by the >>> hardware, as a result of each POLLPRI event. So in fact in >>> the same time it should report both according to our requirements >>> which is impossible. Do we need three brightness files ? >> >> I don't think so, current_brightness actually is an accurate >> name, if the brightness was last changed by writing from >> sysfs, the keyboard backlight will honor that and the current_brightness >> attribute will show the brightness last set through writing it, >> which matches the actual current brightness of the keyboard backlight. >> >> Likewise if it was changed with the hotkey last then the keyboard >> backlight brightness will be changed and reading from current_brightness >> will return the new actual brightness. Basically reading from this >> file will be no different then reading from the normal "brightness" >> file the difference will be in that it is poll-able and that >> writing 0 turns off the LED without stopping blinking. > > If so then when software blinking enabled, it will return 0 on low > blink cycle no matter what current brightness level is.
For software blinking there will not be a current_brightness atrribute, as we will only add that for LEDs with poll-able triggers.
Also during the low cycle the LED is off, so its brightness at the moment of reading (iow currently) is 0.
Regards,
Hans
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