linux-kernel - Re: [RESEND PATCH v3 0/4] backlight: pwm_bl: support linear interpolation and brightness to human eye

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Date:   Mon, 18 Jun 2018 07:20:05 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        Doug Anderson <dianders@...gle.com>,
        Pavel Machek <pavel@....cz>, Rob Herring <robh+dt@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Brian Norris <briannorris@...gle.com>,
        Guenter Roeck <groeck@...gle.com>,
        Alexandru Stan <amstan@...gle.com>, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com
Subject: Re: [RESEND PATCH v3 0/4] backlight: pwm_bl: support linear
 interpolation and brightness to human eye

On Mon, 09 Apr 2018, Enric Balletbo i Serra wrote:

> Dear all,
> 
> This series is a third patchset (resend )integrating the requested
> changes.
> 
> The first and second patch what tries to solve is the problem of
> granularity for high resolution PWMs. The idea is simple interpolate
> between 2 brightness values so we can have a high PWM duty cycle (a
> 16 bits PWM is up to 65535 possible steps) without having to list
> out every possible value in the dts. I think that this patch is
> required to not break backward compatibility, to be more flexible and
> also extend the functionality to be able to use high resolution PWM
> with enough steps to have a good UI experience in userspace.
> 
> The thirth and fourth patch is a bit more ambicious, the idea is let
> decide the driver the brightness-levels required in function of the PWM
> resolution. To do this create a brightness-levels table filled with the
> CIE 1931 algorithm values to convert brightness to PWM duty cycle.
> 
> More detailed info is available in the commit message of every patch.
> 
> Both functionalities were tested on a Samsung Chromebook Plus (that has
> a 16 bits PWM) and a SL50 device (with a 8 bits PWM)
> 
> Waiting for your feedback.
> 
> Best regards
> 
> Enric Balletbo i Serra (4):
>   backlight: pwm_bl: linear interpolation between brightness-levels
>   dt-bindings: pwm-backlight: add a num-interpolation-steps property.
>   backlight: pwm_bl: compute brightness of LED linearly to human eye.
>   dt-bindings: pwm-backlight: move brightness-levels to optional.
> 
>  .../bindings/leds/backlight/pwm-backlight.txt      |  34 ++-
>  drivers/video/backlight/pwm_bl.c                   | 232 +++++++++++++++++++--
>  2 files changed, 246 insertions(+), 20 deletions(-)

All applied for v4.18, thanks.

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