Re: [resend] drm/i915: Check incoming alignment for unfenced buffers (on i915gm)

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On Tue, 2017-10-31 at 10:36 +0000, Chris Wilson wrote:
> In case the object has changed tiling between calls to execbuf, we need
> to check if the existing offset inside the GTT matches the new tiling
> constraint. We even need to do this for "unfenced" tiled objects, where
> the 3D commands use an implied fence and so the object still needs to
> match the physical fence restrictions on alignment (only required for
> gen2 and early gen3).
> 
> In commit 2889caa92321 ("drm/i915: Eliminate lots of iterations over
> the execobjects array"), the idea was to remove the second guessing and
> only set the NEEDS_MAP flag when required. However, the entire check
> for an unusable offset for fencing was removed and not just the
> secondary check. I.e.
> 
> 	/* avoid costly ping-pong once a batch bo ended up non-mappable */
>         if (entry->flags & __EXEC_OBJECT_NEEDS_MAP &&
>             !i915_vma_is_map_and_fenceable(vma))
>                 return !only_mappable_for_reloc(entry->flags);
> 
> was entirely removed as the ping-pong between execbuf passes was fixed,
> but its primary purpose in forcing unaligned unfenced access to be
> rebound was forgotten.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103502
> Fixes: 2889caa92321 ("drm/i915: Eliminate lots of iterations over the execobjects array")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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