Re: [PATCH v3 3/4] backlight: pwm_bl: compute brightness of LED linearly to human eye.

Pavel Machek
2019-06-12T09:54:13Z

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On Tue 2019-06-11 15:30:19, Matthias Kaehlcke wrote:
> On Tue, Jun 11, 2019 at 09:55:30AM -0700, Brian Norris wrote:
> > On Tue, Jun 11, 2019 at 3:49 AM Daniel Thompson
> > <daniel.thompson@linaro.org> wrote:
> > > This is a long standing flaw in the backlight interfaces. AFAIK generic
> > > userspaces end up with a (flawed) heuristic.
> >
> > Bingo! Would be nice if we could start to fix this long-standing flaw.
>
> Agreed!
>
> How could a fix look like, a sysfs attribute? Would a boolean value
> like 'logarithmic_scale' or 'linear_scale' be enough or could more
> granularity be needed?

I'd expect attribute "scale" with values "linear" or "logarithmic".

> The new attribute could be optional (it only exists if explicitly
> specified by the driver) or be set to a default based on a heuristic
> if not specified and be 'fixed' on a case by case basis. The latter
> might violate "don't break userspace" though, so I'm not sure it's a
> good idea.

I'd do it only when we explicitely know. We don't want it to be buggy.

And I guess we should decide what interface we really want? (Linear?
Logarithmic?) And make new drivers do that.

Best regards,
Pavel
--
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