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

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Date:   Tue, 20 Mar 2018 19:22:12 +0800
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Enric Balletbo Serra <eballetbo@...il.com>
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        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>,
        Lee Jones <lee.jones@...aro.org>,
        Alexandru Stan <amstan@...gle.com>, linux-leds@...r.kernel.org,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, kernel@...labora.com
Subject: Re: [PATCH v3 0/4] backlight: pwm_bl: support linear interpolation
 and brightness to human eye

On Mon, Mar 19, 2018 at 05:04:31PM +0100, Enric Balletbo Serra wrote:
> Hi Daniel,
> 
> Gentle ping for this series, there is any possibility you have a
> chance to review it? Let me know if you want I change something.

I haven't got it in my TODO backlog... which means either I mistakenly
deleted it when it went through originally or that I deliberately deleted
it because I thought a v4 was coming along soon.

I could go diving through the archives if I need to but were there other
pending changes for this patchset?


Daniel.


> 
> Thanks,
>   Enric
> 
> 2018-02-08 12:30 GMT+01:00 Enric Balletbo i Serra
> <enric.balletbo@...labora.com>:
> > Dear all,
> >
> > This series is a third patchset 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 compability, 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(-)
> >
> > --
> > 2.15.1
> >