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

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Date:	Fri, 16 Aug 2013 08:49:10 +1000
From:	Dave Airlie <airlied@...il.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	Dave Airlie <airlied@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [PATCH] i915: Update VGA arbiter support for newer devices

On Fri, Aug 16, 2013 at 8:43 AM, Alex Williamson
<alex.williamson@...hat.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.

Dave.
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