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

[Pavel Machek <pavel@ucw.cz>]

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Hi!

> >>>>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).
> >>
> >>I'd drop the trigger approach due to the mess it can make in peoples'
> >>minds due to the fact that LED class device handles trigger events
> >>generated by itself.
> >
> >We can teach people. IMO the LED that changes itself is special, and
> >trigger explains that nicely to the userspace. Plus, it allows us to
> >keep this functionality out of the core.
> 
> Please refer to the downsides of this appraoch:
> 
> - lack of information if given LED class device supports hw
>   generated POLLPRI events

Userspace can plainly see that a trigger is active, and knows to
expect 

> - impossible to apply other trigger while polling

That's a good thing. We _don't_ want polling to be active when trigger
such as "CPU active" is active. We want userspace to monitor hardware
events but not software ones.

> >>I'd add a file hw_brightness_change or async_brightness or something
> >>similar and make it only readable/pollable. current_brightness is
> >>ambiguous and questionable.
> >
> >Well, exact name is not too important...
> 
> The name should clearly explain the file purpose. I bet that we would
> see many questions once the file appeared in the mainline.
> Also, I'm afraid that I wouldn't be able to explain this name in
> few simple words, without daunting the listener, or even triggering
> the discussion on brightness shortcomings we've already gone through.

Well, feel free to suggest non-confusing name.

Unfortunately, yes, we'll need to do some explaining, as existing
"brightness" behaviour is already pretty tricky / confusing /
counterintuitive.

Lets at least make sure new additions are clean and simple.

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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