[PATCH v5 3/3] drm/xe/guc_ads: use uncached mapping for UM queue BO

The HW unit that writes fault descriptors into the UM queue ring buffer
may not be coherent with the CPU cache.  If a descriptor write is still
sitting in a GPU L3 cache line when GuC reads the slot, GuC sees the
stale (all-zero) content from DRAM and forwards an invalid descriptor to
the driver (Faulted Address = 0, ASID = 0).

Mark the UM queue BO as uncached (XE_BO_FLAG_NEEDS_UC) so that writes
bypass the cache and are immediately visible to GuC.

Cc: Gwan-gyeong Mun <[email protected]>
Cc: Matthew Auld <[email protected]>
Signed-off-by: Jia Yao <[email protected]>
---
 drivers/gpu/drm/xe/xe_guc_ads.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_guc_ads.c b/drivers/gpu/drm/xe/xe_guc_ads.c
index 57a0614dbf6d..0b4524a1f7b1 100644
--- a/drivers/gpu/drm/xe/xe_guc_ads.c
+++ b/drivers/gpu/drm/xe/xe_guc_ads.c
@@ -464,7 +464,8 @@ int xe_guc_ads_init(struct xe_guc_ads *ads)
 		u32 um_flags = XE_BO_FLAG_VRAM_IF_DGFX(tile) |
 			       XE_BO_FLAG_GGTT |
 			       XE_BO_FLAG_GGTT_INVALIDATE |
-			       XE_BO_FLAG_PINNED_NORESTORE;
+			       XE_BO_FLAG_PINNED_NORESTORE |
+			       XE_BO_FLAG_NEEDS_UC;
 
 		bo = xe_managed_bo_create_pin_map(xe, tile, um_size, um_flags);
 		if (IS_ERR(bo))
-- 
2.43.0