[Intel-gfx] [PATCH 4.19.y] drm/i915: Don't use BAR mappings 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 ring buffers should never be mapped
via the BAR on systems with LLC. There are too many caching pitfalls
due to the way BAR accesses are routed. So it is safest to just not
use it.

Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
Fixes: 9d80841ea4c9 ("drm/i915: Allow ringbuffers to be bound anywhere")
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/20230216011101.1909009-3-John.C.Harrison@Intel.com
(cherry picked from commit 65c08339db1ada87afd6cfe7db8e60bb4851d919)
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
(cherry picked from commit 85636167e3206c3fbd52254fc432991cc4e90194)
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 3b8218dd9bb1..979d130b24c4 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1083,7 +1083,7 @@ int intel_ring_pin(struct intel_ring *ring,
 	if (unlikely(ret))
 		return ret;
 
-	if (i915_vma_is_map_and_fenceable(vma))
+	if (i915_vma_is_map_and_fenceable(vma) && !HAS_LLC(vma->vm->i915))
 		addr = (void __force *)i915_vma_pin_iomap(vma);
 	else
 		addr = i915_gem_object_pin_map(vma->obj, map);
@@ -1118,7 +1118,7 @@ void intel_ring_unpin(struct intel_ring *ring)
 	/* Discard any unused bytes beyond that submitted to hw. */
 	intel_ring_reset(ring, ring->tail);
 
-	if (i915_vma_is_map_and_fenceable(ring->vma))
+	if (i915_vma_is_map_and_fenceable(ring->vma) && !HAS_LLC(ring->vma->vm->i915))
 		i915_vma_unpin_iomap(ring->vma);
 	else
 		i915_gem_object_unpin_map(ring->vma->obj);
-- 
2.39.1