drm/i915: Don't use stolen memory for ring buffers with LLC

Direction from hardware is that stolen memory should never be used for
ring buffer allocations on platforms with LLC. There are too many
caching pitfalls due to the way stolen memory accesses are routed. So
it is safest to just not use it.

Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Fixes: c58b735fc762 ("drm/i915: Allocate rings from stolen")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v4.9+
Tested-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216011101.1909009-2-John.C.Harrison@Intel.com

diff --git a/drivers/gpu/drm/i915/gt/intel_ring.c b/drivers/gpu/drm/i915/gt/intel_ring.c
index 15ec64d..fb1d259 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_ring.c
+++ b/drivers/gpu/drm/i915/gt/intel_ring.c
@@ -116,7 +116,7 @@ static struct i915_vma *create_ring_vma(struct i915_ggtt *ggtt, int size)
 
        obj = i915_gem_object_create_lmem(i915, size, I915_BO_ALLOC_VOLATILE |
                                          I915_BO_ALLOC_PM_VOLATILE);
-       if (IS_ERR(obj) && i915_ggtt_has_aperture(ggtt))
+       if (IS_ERR(obj) && i915_ggtt_has_aperture(ggtt) && !HAS_LLC(i915))
                obj = i915_gem_object_create_stolen(i915, size);
        if (IS_ERR(obj))
                obj = i915_gem_object_create_internal(i915, size);