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    SubjectRe: [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@canonical.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@canonical.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@canonical.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@canonical.com>
    > >> >>
    > >> >> Works for me.
    > >> >>
    > >> >> Tested-by: Grant Likely <grant.likely@secretlab.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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