linux-kernel - Re: [PATCH] backlight: add support for disabling backlights via sysfs

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Date:	Fri, 29 Jun 2012 14:24:38 +0200
From:	Corentin Chary <corentin.chary@...il.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Richard Purdie <rpurdie@...ys.net>, linux-kernel@...r.kernel.org,
	platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH] backlight: add support for disabling backlights via sysfs

On Thu, Jun 28, 2012 at 9:36 PM, Matthew Garrett <mjg59@...f.ucam.org> wrote:
> On Thu, Jun 28, 2012 at 02:30:17PM -0500, Seth Forshee wrote:
>
>> I actually don't think Corentin's solution is a bad one. It does suffer
>> from a couple of shortcomings though. First, it only works for broken
>> ACPI backlights, and some platforms have other backlight interfaces that
>> are broken (e.g. the i915 backlight on the MacBook Pro 8,2). Second,
>> marking backlights as broken in the kernel necessitates ever-expanding
>> dmi blacklists in some of the platform drivers, unless we can get
>> vendors to stop providing broken backlight interfaces.
>
> Userspace should already be prioritising platform interfaces over raw
> interfaces, so if gmux works on the Mac then there's no problem.

Hehe, sometime the platform interface doesn't work and the raw does.
That's the case on various samsung-laptop since we have absolutely no
documentation about SABI and no known way to probe if the
implementation is working or not. But anyway, for samsung-laptop it's
disabled by default in favor of acpi_video (which is also broken most
of the time on samsung laptops).

> DMI
> lists should, broadly speaking, be unnecessary - they're mostly a
> symptom of us not understanding how the hardware is expected to work.
>
>> I'm all for fixing integration bugs in the ACPI backlight
>> implementations if we can, but some vendor implementations are just
>> flat-out broken, and it isn't always possible to get vendor cooperation.
>> In the case of Toshiba I've tried reaching out to them to work on ACPI
>> integration issues, but they flat out refused.
>
> We already know that our implementation of the IGD opregion is broken,
> but Intel won't hand over newer versions of the spec. If you see
> problems with the acpi backlight interface on Intel graphics then that
> should be the default assumption.
>
> --
> Matthew Garrett | mjg59@...f.ucam.org



-- 
Corentin Chary
http://xf.iksaif.net
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