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

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