[Intel-gfx] [PATCH 5.4.y] drm/i915: Don't use stolen memory for ring buffers with LLC

[John.C.Harrison at Intel.com]

From: John Harrison <John.C.Harrison at Intel.com>

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 at Intel.com>
Fixes: c58b735fc762 ("drm/i915: Allocate rings from stolen")
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Jani Nikula <jani.nikula at linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
Cc: intel-gfx at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v4.9+
Tested-by: Jouni Högander <jouni.hogander at intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216011101.1909009-2-John.C.Harrison@Intel.com
(cherry picked from commit f54c1f6c697c4297f7ed94283c184acc338a5cf8)
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
(cherry picked from commit 690e0ec8e63da9a29b39fedc6ed5da09c7c82651)
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
---
 drivers/gpu/drm/i915/gt/intel_ringbuffer.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_ringbuffer.c b/drivers/gpu/drm/i915/gt/intel_ringbuffer.c
index 808269b2108f..125f7bb67bee 100644
--- a/drivers/gpu/drm/i915/gt/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/gt/intel_ringbuffer.c
@@ -1268,10 +1268,11 @@ static struct i915_vma *create_ring_vma(struct i915_ggtt *ggtt, int size)
 {
 	struct i915_address_space *vm = &ggtt->vm;
 	struct drm_i915_private *i915 = vm->i915;
-	struct drm_i915_gem_object *obj;
+	struct drm_i915_gem_object *obj = NULL;
 	struct i915_vma *vma;
 
-	obj = i915_gem_object_create_stolen(i915, size);
+	if (!HAS_LLC(i915))
+		obj = i915_gem_object_create_stolen(i915, size);
 	if (!obj)
 		obj = i915_gem_object_create_internal(i915, size);
 	if (IS_ERR(obj))
-- 
2.39.1