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

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Message-ID: <20120229220809.GC20565@ubuntu-macmini>
Date:	Wed, 29 Feb 2012 16:08:09 -0600
From:	Seth Forshee <seth.forshee@...onical.com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	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 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. 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.

Seth

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