[Intel-gfx] [PATCH] drm/i915: Force uncached PPAT for debugging purposes.

[Chris Wilson]

On Mon, Feb 27, 2017 at 05:18:08PM -0800, Ben Widawsky wrote:
> On 17-02-27 17:12:07, Rodrigo Vivi wrote:
> >Many screen corruptions and hangs in the past were somehow
> >related to the caches. In many situations forcing the uncached
> >was useful at least to narrow down the issue by confirming it
> >was cache related.
> >
> >Instead of having to hardcode it everytime that we suspect on
> >this table let's provide a mechanism to disable these
> >cache leves on this private table (PPAT).
> >
> >Cc: Ben Widawsky <benjamin.widawsky at intel.com>
> >Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> >Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> 
> I think this is a cool idea, it could equally be achieved by modifying the PTE
> encoding function. In my head, modifying the pte encode makes more sense since
> it applies to all legacy context, advanced context, and ggtt entries.

Changing the mocs table is not the same as changing the PTE. Both are
useful for different types of bugs.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre