drm/xe: Add mmio read before GGTT invalidate

On LNL without a mmio read before a GGTT invalidate the GuC can
incorrectly read the GGTT scratch page upon next access leading to jobs
not getting scheduled. A mmio read before a GGTT invalidate seems to fix
this. Since a GGTT invalidate is not a hot code path, blindly do a mmio
read before each GGTT invalidate.

Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: stable@vger.kernel.org
Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Reported-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/3164
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241023221200.1797832-1-matthew.brost@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
(cherry picked from commit 5a710196883e0ac019ac6df2a6d79c16ad3c32fa)
[ Fix conflict with mmio vs gt argument ]
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

diff --git a/drivers/gpu/drm/xe/xe_ggtt.c b/drivers/gpu/drm/xe/xe_ggtt.c
index 2895f154654cac6338460eae5384057029e615ff..ff19eca5d358b325a4ed07e7ef812c4ff3d88a0c 100644 (file)
--- a/drivers/gpu/drm/xe/xe_ggtt.c
+++ b/drivers/gpu/drm/xe/xe_ggtt.c
@@ -397,6 +397,16 @@ static void ggtt_invalidate_gt_tlb(struct xe_gt *gt)
 
 static void xe_ggtt_invalidate(struct xe_ggtt *ggtt)
 {
+       struct xe_device *xe = tile_to_xe(ggtt->tile);
+
+       /*
+        * XXX: Barrier for GGTT pages. Unsure exactly why this required but
+        * without this LNL is having issues with the GuC reading scratch page
+        * vs. correct GGTT page. Not particularly a hot code path so blindly
+        * do a mmio read here which results in GuC reading correct GGTT page.
+        */
+       xe_mmio_read32(xe_root_mmio_gt(xe), VF_CAP_REG);
+
        /* Each GT in a tile has its own TLB to cache GGTT lookups */
        ggtt_invalidate_gt_tlb(ggtt->tile->primary_gt);
        ggtt_invalidate_gt_tlb(ggtt->tile->media_gt);