[Intel-gfx] [PATCH] allocate & enable MCHBAR if needed

Jesse Barnes jbarnes at virtuousgeek.org
Thu Feb 12 18:06:10 CET 2009

On Thursday, February 12, 2009 3:38 am Chris Wilson wrote:
> On Wed, 2009-02-11 at 17:54 -0800, Jesse Barnes wrote:
> > I noticed on my Eee 901 that the i915 DRM driver wasn't reading the
> > MCHBAR reg at startup time, and so it would disable tiling.  For decent
> > performance, especially on an Eee-like platform, tiling is a must.  So I
> > put this patch together to allocate MCHBAR space and enable it if
> > necessary.
> >
> > In combination with the pre-965 tiling patches in the tree now, you
> > should see a big performance improvement if you have an affected machine.
> >
> > (Note to Eric: don't merge this until someone else confirms it works for
> > them too.)
> No joy, I'm afraid. This patch fails to enable tiling on my el cheapo
> eee 700. Just to reaffirm with the previous patch I get a performance
> boost of around a factor of 20x over this version.
> (And /proc/dri/0/i915_gem_fence indeed reports no tiling). I noticed
> that wasn't any debugging output; is there anything I can do to help?

Hm, yeah I clearly broke something here.  I removed the ACPI check after 
chatting with the ACPI guys.  I intended for the patch to do nothing if the 
MCHBAR is already enabled, but allocate PCI space and enable it if it's not 
enabled.  Maybe the PCI space allocation is failing for you?  If so, we might 
just have to go with the ACPI version.

Jesse Barnes, Intel Open Source Technology Center

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