From: Brian Norris <briannorris@google.com>
To: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Matthias Kaehlcke <mka@chromium.org>, Pavel Machek <pavel@ucw.cz>,
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.
Date: Tue, 11 Jun 2019 09:55:30 -0700 [thread overview]
Message-ID: <CA+ASDXOq7KQ+f4KMh0gaC9hvXaxBDdsbiJxiTbeOJ9ZVaeNJag@mail.gmail.com> (raw)
In-Reply-To: <20190611104913.egsbwcedshjdy3m5@holly.lan>
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.
> Basically devices with a narrow range of choices can be assumed to be
> logarithmic
That's (almost, see below) exactly what we have.
(And this is what Matthias is fighting against, now that we're
implementing both "large number of data points" and "pre-curved" at
the same time. We will have to either adapt the heuristic, or else
adapt our device trees to fit the heuristic.)
> Systems are coming along that allow us to animate the change of
> brightness (part of the reason for interpolated tables is to
> permit smooth animation rather than because the user explicitly wants
> to set the brightness to exactly 1117).
Chrome OS has done this for a long time. So "coming along" is a bit late ;)
Also, I believe Chrome OS will do animation/smoothing for all tables
(small or large) where it can: even for the small tables.
> These systems are often
> logarithmic but with a wide range of values.
NB: Chrome OS happens to use a polynomial formula (exponent = 2 or
0.5, depending on how you look at it), not logarithmic. You can see it
in all its (non)glory here:
https://chromium.googlesource.com/chromiumos/platform2/+/ee015853b227cf265491bd80ccf096b188490529/power_manager/powerd/policy/internal_backlight_controller.cc#451
Regards,
Brian
next prev parent reply other threads:[~2019-06-11 16:55 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-08 11:30 [PATCH v3 0/4] backlight: pwm_bl: support linear interpolation and brightness to human eye Enric Balletbo i Serra
2018-02-08 11:30 ` [PATCH v3 1/4] backlight: pwm_bl: linear interpolation between brightness-levels Enric Balletbo i Serra
2018-04-06 15:46 ` Daniel Thompson
2018-02-08 11:30 ` [PATCH v3 2/4] dt-bindings: pwm-backlight: add a num-interpolation-steps property Enric Balletbo i Serra
2018-02-18 22:49 ` Rob Herring
2018-02-08 11:30 ` [PATCH v3 3/4] backlight: pwm_bl: compute brightness of LED linearly to human eye Enric Balletbo i Serra
2018-04-06 15:51 ` Daniel Thompson
2019-06-07 22:19 ` Matthias Kaehlcke
2019-06-08 21:02 ` Pavel Machek
2019-06-10 10:00 ` Enric Balletbo i Serra
2019-06-10 20:39 ` Matthias Kaehlcke
2019-06-10 21:02 ` Enric Balletbo i Serra
2019-06-10 21:54 ` Matthias Kaehlcke
2019-06-10 20:52 ` Matthias Kaehlcke
2019-06-11 10:49 ` Daniel Thompson
2019-06-11 16:55 ` Brian Norris [this message]
2019-06-11 22:30 ` Matthias Kaehlcke
2019-06-12 9:54 ` Pavel Machek
2019-06-12 11:03 ` Daniel Thompson
2019-06-12 19:26 ` Matthias Kaehlcke
2019-06-12 19:47 ` Daniel Thompson
2019-06-12 21:59 ` Matthias Kaehlcke
2019-06-17 13:01 ` Pavel Machek
2019-06-17 20:03 ` Matthias Kaehlcke
2018-02-08 11:30 ` [PATCH v3 4/4] dt-bindings: pwm-backlight: move brightness-levels to optional Enric Balletbo i Serra
2018-03-19 16:04 ` [PATCH v3 0/4] backlight: pwm_bl: support linear interpolation and brightness to human eye Enric Balletbo Serra
2018-03-20 11:22 ` Daniel Thompson
2018-03-20 12:13 ` Enric Balletbo Serra
2018-04-06 15:54 ` Daniel Thompson
2018-04-09 8:17 ` Lee Jones
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