Re: [PATCH 2/3] drm/i915: Fix obj->map_and_fenceable for ppgtt

[Ben Widawsky <benjamin.widawsky@intel.com>]

On Sat, Aug 09, 2014 at 05:37:23PM +0100, Chris Wilson wrote:
> With ppgtt, it is no longer correct to mark an object as
> map_and_fenceable if we simply unbind it from the global gtt. This has
> consequences during execbuffer where we simply use
> obj->map_and_fenceable in use_cpu_reloc() to decide which access method
> to use for writing into the object. Now for a ppgtt object,
> map_and_fenceable will be true when it is not bound into the ggtt but
> only in a ppgtt, leading to an invalid access on a non-llc architecture.

The last sentence confused me for some reason. I think the first two
sentences were perfectly succinct in describing the problem.

> 
> v2: Revamp and resend to ease future patches.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Ben Widawsky <benjamin.widawsky@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

I didn't read the patch closely, but the problem is clear. It seems like
the one hunk:
> -     if (use_cpu_reloc(obj))
> +     if (use_cpu_reloc(obj) || !i915_gem_obj_ggtt_bound(obj))

would be sufficient to fix the problem.

I had a local solution at one point (I'm too lazy to check what I've
sent out these days) where I turned map_and_fenceable into a getter(). I
thought that looked pretty nice as well.

lgtm

[snip]

-- 
Ben Widawsky, Intel Open Source Technology Center