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

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Message-ID: <20120229195042.GB20565@ubuntu-macmini>
Date:	Wed, 29 Feb 2012 13:50:42 -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 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.

What about userspace? I don't know about other desktops, but in the past
gnome-settings-daemon had a list to determine which backlight to prefer,
so it would have been possible to insert gmux_backlight in the list
above acpi_video0. It seems to have been changed now to use the
backlight type, preferring a firmware backlight to a platform one, which
would prefer acpi_video0 to gmux_backlight. I don't know know what the
solution is under this paradigm.

Seth
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