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

From: Pavel Machek
Date: Mon Jun 17 2019 - 09:06:50 EST


> > Certainly "linear" (this device will work more or less correctly if the
> > userspace applies perceptual curves). Not sure about logarithmic since
> > what is actually useful is something that is "perceptually linear"
> > (logarithmic is merely a way to approximate that).
> >
> > I do wonder about a compatible string like most-detailed to
> > least-detailed description. This for a PWM with the auto-generated
> > tables we'd see something like:
> >
> > cie-1991,perceptual,non-linear
> >
> > For something that is non-linear but we are not sure what its tables are
> > we can offer just "non-linear".
> Thanks for the feedback!
> It seems clear that we want a string for the added flexibility. I can
> work on a patch with the compatible string like description you
> suggested and we can discuss in the review if we want to go with that
> or prefer something else.

Compatible-like string seems overly complicated.

> > Instead one valid value for the sysfs should be "unknown" and this be
> > the default for drivers we have not analysed (this also makes it easy to
> > introduce change here).
> An "unknown" value sounds good, it allows userspace to just do what it
> did/would hace done before this attribute existed.

What about simply not presenting the attribute when we don't have the
(cesky, pictures)

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