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

[Seth Forshee <seth.forshee@canonical.com>]

On Mon, Mar 12, 2012 at 03:07:17PM +0000, Matthew Garrett wrote:
> > We also have the problem of gmux_backlight versus acpi_video. On most
> > machines with a gmux the acpi_video backlight interface is present but
> > just doesn't work. This problem isn't just limited to Apples. I'm of the
> > opinion that we need a more generalized solution for arbitrating between
> > the backlight interfaces present on a given machine, but I haven't had a
> > chance to really think about what that would look like.
> 
> The ACPI code appears to be trapping into system management mode, so 
> figuring out what it's meant to do is going to be awkward. I think 
> having a hook in the ACPI video driver to deregister it in cases where 
> we know it doesn't work is legitimate, but since it presumably works 
> under Windows it'd be nice to figure out what's broken about it.

Why do you presume it works under Windows? Boot camp installs a pile of
drivers for Windows, one of those could be a driver for the backlight. I
don't know either way. But it's pretty clear that MacOS is using the
gmux for the backlight when it is present from the reverse engineering
work done by others.

Seth