linux-kernel - Re: [PATCH] samsung-laptop: unregister ACPI video module for some well known laptops

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Message-ID: <20120406143455.GC8666@thinkpad-t410>
Date:	Fri, 6 Apr 2012 09:34:55 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>,
	Corentin Chary <corentin.chary@...il.com>
Cc:	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux acpi <linux-acpi@...r.kernel.org>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH] samsung-laptop: unregister ACPI video module for some
 well known laptops

On Fri, Apr 06, 2012 at 11:42:18AM +0200, Corentin Chary wrote:
> On Tue, Mar 27, 2012 at 1:21 PM, Matthew Garrett <mjg59@...f.ucam.org> wrote:
> > On Tue, Mar 27, 2012 at 11:11:18AM +0200, Corentin Chary wrote:
> >> Matthew, is this one ok ? I really hope this patch can go in 3.4 so we
> >> don't introduce a regression for old laptops.
> >
> > Yes, I've got this now.
> >
> > Thanks,
> 
> 
> A user just found a DSDT which is broken by this way of doing things
> (this is not really a regression since it was also broken before).
> 
> _BCL contains a wierd "Or (VDRV, 0x02, VDRV)".
> So if you call _BLC once (video.ko will), it set a flag that affect
> the behavior of all backlight related stuff, and it breaks
> samsung-laptop's backlight even if samsung-laptop unload the acpi
> backlight.
> Using acpi_backlight=vendor solves that since it prevents the module
> from being loaded. My previous patch also fix that since it use
> acpi_backlight= mechanism.
> 
> Do you think using acpi_backlight=vendor is a good enought solution
> here ? Should we use my first patch instead ?

I've recently noticed another problem with using acpi_video_unregister()
to disable known broken backlights -- another module might call
acpi_video_register() and make it reappear. i915 does this, so when I
EFI boot the MacBook Pro 8,2 the acpi backlights reappear (under a BIOS
compatible boot the Intel GPU doesn't show up on the bus).

So Corentin's solution does seem like a better way to go, or else
something similar that forces the ACPI video driver to behave as with
acpi_video=vendor.

Seth

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