linux-kernel - Re: [PATCH] i915: Quirk out disconnected backlight

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Date:	Fri, 14 Sep 2012 14:12:19 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	David Airlie <airlied@...ux.ie>,
	Matthew Garrett <mjg@...hat.com>
Subject: Re: [PATCH] i915: Quirk out disconnected backlight

On Fri, 2012-09-14 at 14:09 +0100, Grant Likely wrote:
> On Fri, Sep 14, 2012 at 2:01 PM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> > On Fri, 14 Sep 2012 13:57:06 +0100, Grant Likely <grant.likely@...retlab.ca> wrote:
> >> Some platforms (for instance MacbookPros) have custom backlight drivers
> >> and don't use the integrated i915 backlight control. This patch adds a
> >> quirk to disable registering the intel backlight when unused on a
> >> platform.
> >>
> >> Tested on MacbookPro8,3. Without this patch both the intel_backlight and
> >> gmux_backlight devices get registered and userspace doesn't know which
> >> it should use.
> >
> > Userspace is informed throught the backlight/type property.
> 
> Perhaps, but userspace (Ubuntu) isn't doing anything with it, and it
> still remains that it makes no sense whatsoever to register a
> backlight device that doesn't exist. 

Indeed. Userspace (well, gnome-settings-daemon) will use the backlight
provided by X, in preference to anything it finds
in /sys/class/backlight. So if the Intel one is present (and thus
exposed via X) then userspace will never bother with comparing types and
choosing the sanest backlight to use.

See https://bugzilla.redhat.com/show_bug.cgi?id=752595

-- 
dwmw2

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