linux-kernel - Re: [PATCH v2] platform/x86: Add driver for Apple gmux device

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Message-ID: <CACxGe6tLCYhuiAH1Q1PoWTzFLmZ0watw==0g76J1hS-Qurzyrw@mail.gmail.com>
Date:	Wed, 29 Feb 2012 16:32:28 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Grant Likely <grant.likely@...retlab.ca>,
	Matthew Garrett <mjg@...hat.com>,
	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] platform/x86: Add driver for Apple gmux device

On Wed, Feb 29, 2012 at 4:08 PM, Seth Forshee
<seth.forshee@...onical.com> wrote:
> On Wed, Feb 29, 2012 at 03:23:20PM -0600, Grant Likely wrote:
>> On Wed, Feb 29, 2012 at 1:50 PM, Seth Forshee
>> <seth.forshee@...onical.com> wrote:
>> > On Wed, Feb 29, 2012 at 12:43:23PM -0600, Grant Likely wrote:
>> >> On Wed, Feb 29, 2012 at 11:53 AM, Seth Forshee
>> >> <seth.forshee@...onical.com> wrote:
>> >> > On Wed, Feb 29, 2012 at 11:46:39AM -0600, Grant Likely wrote:
>> >> >> On Wed, Feb 22, 2012 at 8:37 AM, Seth Forshee
>> >> >> <seth.forshee@...onical.com> wrote:
>> >> >> > Apple laptops with hybrid graphics have a device named gmux that
>> >> >> > controls the muxing of the LVDS panel between the GPUs as well as screen
>> >> >> > brightness. This driver adds support for the gmux device. Only backlight
>> >> >> > control is supported initially.
>> >> >> >
>> >> >> > Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
>> >> >>
>> >> >> Works for me.
>> >> >>
>> >> >> Tested-by: Grant Likely <grant.likely@...retlab.ca>
>> >> >>
>> >> >> Now I just need to figure out how to get the desktop backlight widget
>> >> >> to use gmux_backlight instead of acpi_video0...
>> >> >
>> >> > The easy way is to pass acpi_backlight=vendor to the kernel, then you
>> >> > won't have acpi_vidoe0.
>> >>
>> >> That did it, thanks.  I'm assume something is in the works to set it
>> >> up automatically?
>> >
>> > Not that I'm aware of. A number machines have this problem, that the
>> > standard ACPI backlight interfaces are implemented but don't work. This
>> > generally isn't detectable in software; with the Apples at least
>> > everything looks like it's working except that the brightness doesn't
>> > change (but not all Apple laptops are affected, so qurking based on
>> > manufacturer wouldn't work). All we're left with is DMI quirking, which
>> > isn't practical. Maybe we could add something so a platform driver can
>> > tell acpi_video that it knows the ACPI backlight doesn't work, but I
>> > think on some platforms that still is going to be based off of DMI
>> > information.
>>
>> blacklisting based on specific product name (ie. MacBookPro8,*) or
>> machine model is probably the best.  It wouldn't be the first
>> blacklist in the linux kernel.
>
> I think the blacklist would have to be against specific product names.
> For example, the MacBook Pro 8,1 has a working acpi_video backlight and
> no gmux_backlight, the 8,2 has both but only gmux_backlight works, and I
> suspect the 8,3 is the same as the 8,2.

I have the 8,3, and my testing confirms that.

> We'd probably end up with an
> entry in the blacklist for every single model whose acpi_video backlight
> doesn't work, adding entries for each new generation of MacBooks.
>
> And if we start blacklisting Macs we'd have start doing it for other
> machines too, I guess. From what I've seen, open-ended blacklists like
> this get nacked pretty consistently nowadays.

An alternative would be to blacklist or disable acpi0_backlight when
the apple-gmux driver loads.  I don't know how acceptable that is, but
I also don't have much sympathy for nacking blacklists if there isn't
a viable alternative.

g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
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