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Date:   Mon, 17 Jun 2019 15:01:51 +0200
From:   Pavel Machek <pavel@ucw.cz>
To:     Matthias Kaehlcke <mka@chromium.org>
Cc:     Daniel Thompson <daniel.thompson@linaro.org>,
        Brian Norris <briannorris@google.com>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        Doug Anderson <dianders@google.com>,
        Rob Herring <robh+dt@kernel.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        Richard Purdie <rpurdie@rpsys.net>,
        Jacek Anaszewski <jacek.anaszewski@gmail.com>,
        Guenter Roeck <groeck@google.com>,
        Lee Jones <lee.jones@linaro.org>,
        Alexandru Stan <amstan@google.com>, linux-leds@vger.kernel.org,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        kernel@collabora.com
Subject: Re: [PATCH v3 3/4] backlight: pwm_bl: compute brightness of LED
 linearly to human eye.
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Hi!

> > 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).
> >=20
> > 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:
> >=20
> > cie-1991,perceptual,non-linear
> >=20
> > For something that is non-linear but we are not sure what its tables are
> > we can offer just "non-linear".
>=20
> Thanks for the feedback!
>=20
> 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).
>=20
> 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
information?
									Pavel
--=20
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo=
g.html

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