Re: [PATCH] i915: Update VGA arbiter support for newer devices

[Alex Williamson <alex.williamson@redhat.com>]

On Fri, 2013-08-16 at 08:49 +1000, Dave Airlie wrote:
> On Fri, Aug 16, 2013 at 8:43 AM, Alex Williamson
> <alex.williamson@redhat.com> wrote:
> > This is intended to add VGA arbiter support for Intel HD graphics on
> > Core processors.  The old GMCH registers no longer exist, so even
> > though it appears that i915 participates in VGA arbitration, it doesn't
> > work.  On Intel HD graphics we already attempt to disable VGA regions
> > of the device.  This makes registering as a VGA client unnecessary since
> > we don't intend to operate differently depending on how many VGA devices
> > are present.  We can disable VGA memory regions by clearing a memory
> > enable bit in the VGA MSR.  That only leaves VGA IO, which we update
> > the VGA arbiter to know that we don't participate in VGA memory
> > arbitration.  We also add a hook on unload to re-enable memory and
> > reinstate VGA memory arbitration.
> 
> I would think there is still a VGA disable bit on the Intel device
> somewhere, we'd just need
> Intel to look in the docs and find it. A bit that can nuke both i/o
> and cmd regs.

The only bit available is in the GGC and is a keyed/locked register that
not only disables VGA memory and I/O, but also modifies the class code
of the device.  Early Core processors didn't lock this, but it's
untouchable in newer ones AFAICT.  Thanks,

Alex