linux-kernel - Re: [PATCH v3 0/4] backlight: Expose brightness curve type through sysfs

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Message-ID: <20190725171726.GD250418@google.com>
Date:   Thu, 25 Jul 2019 10:17:26 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Lee Jones <lee.jones@...aro.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 0/4] backlight: Expose brightness curve type through
 sysfs

On Thu, Jul 25, 2019 at 12:15:41PM +0100, Lee Jones wrote:
> On Mon, 22 Jul 2019, Matthias Kaehlcke wrote:
> 
> > On Tue, Jul 09, 2019 at 12:00:03PM -0700, 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 is currently opaque
> > > to userspace, so userspace often relies on 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 a new sysfs attribute.
> > > 
> > > Matthias Kaehlcke (4):
> > >   MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
> > >   backlight: Expose brightness curve type through sysfs
> > >   backlight: pwm_bl: Set scale type for CIE 1931 curves
> > >   backlight: pwm_bl: Set scale type for brightness curves specified in
> > >     the DT
> > > 
> > >  .../ABI/testing/sysfs-class-backlight         | 26 ++++++++++++++
> > >  MAINTAINERS                                   |  2 ++
> > >  drivers/video/backlight/backlight.c           | 19 ++++++++++
> > >  drivers/video/backlight/pwm_bl.c              | 35 ++++++++++++++++++-
> > >  include/linux/backlight.h                     |  8 +++++
> > >  5 files changed, 89 insertions(+), 1 deletion(-)
> > >  create mode 100644 Documentation/ABI/testing/sysfs-class-backlight
> > 
> > ping, any comments on v3?
> 
> Looks like PATCH 2/4 still needs seeing to.

The patch currently doesn't have any comments.

Do you see any specific things that need improvement? If so, could you
comment on the patch?

Thanks

Matthias