linux-kernel - Re: [PATCH v3 3/4] backlight: pwm_bl: compute brightness of LED linearly to human eye.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190612095413.GA12656@amd>
Date:   Wed, 12 Jun 2019 11:54:13 +0200
From:   Pavel Machek <pavel@....cz>
To:     Matthias Kaehlcke <mka@...omium.org>
Cc:     Brian Norris <briannorris@...gle.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Doug Anderson <dianders@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Richard Purdie <rpurdie@...ys.net>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Guenter Roeck <groeck@...gle.com>,
        Lee Jones <lee.jones@...aro.org>,
        Alexandru Stan <amstan@...gle.com>, linux-leds@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        kernel@...labora.com
Subject: Re: [PATCH v3 3/4] backlight: pwm_bl: compute brightness of LED
 linearly to human eye.

On Tue 2019-06-11 15:30:19, Matthias Kaehlcke wrote:
> On Tue, Jun 11, 2019 at 09:55:30AM -0700, Brian Norris wrote:
> > On Tue, Jun 11, 2019 at 3:49 AM Daniel Thompson
> > <daniel.thompson@...aro.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.
> 
> Agreed!
> 
> How could a fix look like, a sysfs attribute? Would a boolean value
> like 'logarithmic_scale' or 'linear_scale' be enough or could more
> granularity be needed?

I'd expect attribute "scale" with values "linear" or "logarithmic".

> The new attribute could be optional (it only exists if explicitly
> specified by the driver) or be set to a default based on a heuristic
> if not specified and be 'fixed' on a case by case basis. The latter
> might violate "don't break userspace" though, so I'm not sure it's a
> good idea.

I'd do it only when we explicitely know. We don't want it to be buggy.

And I guess we should decide what interface we really want? (Linear?
Logarithmic?) And make new drivers do that.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Download attachment "signature.asc" of type "application/pgp-signature" (182 bytes)