Re: [PATCH v5 2/6] leds: triggers: Add a keyboard backlight trigger

["Pali Rohár" <pali.rohar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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On Sunday 20 November 2016 19:48:02 Hans de Goede wrote:
> HI,
> 
> On 20-11-16 17:21, Pavel Machek wrote:
> > Hi!
> > 
> >>>>>>> Thanks for the patch.
> >>>>>>> 
> >>>>>>> I think we need less generic trigger name.
> >>>>>>> With present name we pretend that all kbd-backlight
> >>>>>>> controllers can change LED brightness autonomously.
> >>>>>>> 
> >>>>>>> How about kbd-backlight-pollable ?
> >>>>>> 
> >>>>>> This is a trigger to control kbd-backlights, in the
> >>>>>> current use-case the brightness change is already done
> >>>>>> by the firmware, hence the set_brightness argument to
> >>>>>> ledtrig_kbd_backlight(), so that we can avoid setting
> >>>>>> it again.
> >>>>>> 
> >>>>>> But I can see future cases where we do want to have some
> >>>>>> event (e.g. a wmi hotkey event on a laptop where the firmware
> >>>>>> does not do the adjustment automatically) which does
> >>>>>> lead to actually updating the brightness.
> >>>>>> 
> >>>>>> So I decided to go with a generic kbd-backlight trigger,
> >>>>>> which in the future can also be used to directly control
> >>>>>> kbd-backlight brightness; and not just to make ot
> >>>>>> poll-able.
> >>>>> 
> >>>>> I thought that kbd-backlight stands for "keyboard backlight",
> >>>> 
> >>>> It does.
> >>>> 
> >>>>> that's why I assessed it is too generic.
> >>>> 
> >>>> The whole purpose of the trigger as implemented is to be
> >>>> generic, as it seems senseless to implement a one off
> >>>> trigger for just the dell / thinkpad case.
> >>>> 
> >>>>> It seems however to be
> >>>>> the other way round - if kbd-backlight means that this is
> >>>>> a trigger only for use with dell-laptop keyboard driver
> >>>>> (I see kbd namespacing prefix in the driver functions) than it
> >>>>> is not generic at all.
> >>>> 
> >>>> The trigger as implemented is generic, if you think
> >>>> otherwise, please let me know which part is not generic
> >>>> according to you.
> >>> 
> >>> I think I was too meticulous here. In the end of the previous
> >>> message I mentioned that we cannot guarantee that all keyboard
> >>> backlight controllers can adjust brightness autonomously.
> >>> Nonetheless, for the ones that cannot do that it would make no
> >>> sense to have a trigger. In view of that this trigger is generic
> >>> enough.
> >>> 
> >>> I'll wait for Pavel's opinion before merging the patch set
> >>> as he was also involved in this whole thread.
> > 
> > If we have a keyboard backlight that may be changed automatically,
> > I'd go for trigger. If we know for sure that hardware will not
> > change brightnes "on its own", I'd not put a trigger there (and
> > polling makes no sense). If we don't know... I guess I'd go for
> > trigger.
> > 
> > We can do various white/blacklists if we really want to..
> > 
> >> As pointed in other email, we do not know if HW really controls
> >> keyboard backlight, so adding "fake" trigger on machines without
> >> HW control is not a good idea.
> > 
> > Well, if we know that hardware will not change the brightness on
> > its own, yes, I'd avoid the trigger. If we don't know (as is
> > common on ACPI machines, I'd keep the trigger).
> 
> Right, this is taken care of by the default_trigger field of the
> led_classdev, we only set the "kbd-backlight" default_trigger on
> (kbd-backlight) LED devices where we know we have a hotkey directly
> controlling the brightness.
> 
> Regards,
> 
> Hans

Hm... now I'm thinking... should not be there a generic readonly led 
trigger named "managed by hw" (or similar name)? Only LED drivers (not 
userspace) could set it and when set it tells that hw could on its own 
change level of LED. Not keyboard backlight specific, but generic for 
led subsystem.

It not this what is needed for keyboard backlight LED drivers?

-- 
Pali Rohár
pali.rohar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org

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