From mboxrd@z Thu Jan 1 00:00:00 1970 From: j.anaszewski@samsung.com (Jacek Anaszewski) Date: Tue, 15 Nov 2016 15:04:38 +0100 Subject: LEDs that change brightness "itself" -- that's a trigger. Re: PM regression with LED changes in next-20161109 In-Reply-To: <9d42546d-5917-891c-2b18-ccf7f7328624@redhat.com> References: <9b476f85-d45e-deb6-335d-fc56f6d90350@redhat.com> <127cdd42-6fd8-c671-60b7-3826b351577f@samsung.com> <15cafbf5-d842-e184-2fd4-65f8272f505a@redhat.com> <20161115103133.GA22860@amd> <4e392d5d-eb10-f285-517e-976a55c3e318@samsung.com> <20161115111154.GA5482@amd> <128aae59-b790-42f1-7d66-81391c9330c3@redhat.com> <20161115114859.GA7018@amd> <9e7d5e0f-c4ca-6930-63b9-83dc28517f33@samsung.com> <9d42546d-5917-891c-2b18-ccf7f7328624@redhat.com> Message-ID: <3bb538bb-3c80-70c7-2c44-46b174c90503@samsung.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. -- Best regards, Jacek Anaszewski