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Date:   Wed, 12 Jun 2019 11:54:13 +0200
From:   Pavel Machek <pavel@ucw.cz>
To:     Matthias Kaehlcke <mka@chromium.org>
Cc:     Brian Norris <briannorris@google.com>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        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.
Message-ID: <20190612095413.GA12656@amd>
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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 gener=
ic
> > > userspaces end up with a (flawed) heuristic.
> >=20
> > Bingo! Would be nice if we could start to fix this long-standing flaw.
>=20
> Agreed!
>=20
> 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
--=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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