linux-kernel - Re: [PATCH v3 2/4] backlight: Expose brightness curve type through sysfs

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Date:   Mon, 2 Sep 2019 10:41:37 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-pwm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Douglas Anderson <dianders@...omium.org>,
        Brian Norris <briannorris@...omium.org>,
        Pavel Machek <pavel@....cz>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>
Subject: Re: [PATCH v3 2/4] backlight: Expose brightness curve type through
 sysfs

On Tue, 09 Jul 2019, Matthias Kaehlcke wrote:

> Backlight brightness curves can have different shapes. The two main
> types are linear and non-linear curves. The human eye doesn't
> perceive linearly increasing/decreasing brightness as linear (see
> also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED
> linearly to human eye"), hence many backlights use non-linear (often
> logarithmic) brightness curves. The type of curve currently is opaque
> to userspace, so userspace often uses more or less reliable heuristics
> (like the number of brightness levels) to decide whether to treat a
> backlight device as linear or non-linear.
> 
> Export the type of the brightness curve via the new sysfs attribute
> 'scale'. The value of the attribute can be 'linear', 'non-linear' or
> 'unknown'. For devices that don't provide information about the scale
> of their brightness curve the value of the 'scale' attribute is 'unknown'.
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
> Feel free to suggest improvements in the documentation :)
> 
> Changes in v3:
> - removed composite strings, only keep 'linear', 'non-linear' and
>   'unknown'
> - updated sysfs attribute documentation
> - updated commit message
> 
> Changes in v2:
> - changed order of brightness scale enums, explicitly make 'unknown' zero
> - minor update of commit message
> - deleted excess blank line after 'backlight_scale_types'
> - s/curves/curve/ in sysfs doc
> ---
>  .../ABI/testing/sysfs-class-backlight         | 26 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  drivers/video/backlight/backlight.c           | 19 ++++++++++++++
>  include/linux/backlight.h                     |  8 ++++++
>  4 files changed, 54 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-class-backlight

Applied, thanks.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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