[PATCH v2] drm/xe: Use ttm_uncached for BO with NEEDS_UC flag

[Michal Wajdeczko <michal.wajdeczko@intel.com>]

We should honor requested uncached mode also at the TTM layer.
Otherwise, we risk losing updates to the memory based interrupts
source or status vectors, as those require uncached memory.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
---
v2: assert that cpu_caching is unset (Matt)
---
 drivers/gpu/drm/xe/xe_bo.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 74294f1b05bc..65c696966e96 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -378,6 +378,15 @@ static struct ttm_tt *xe_ttm_tt_create(struct ttm_buffer_object *ttm_bo,
 	    (xe->info.graphics_verx100 >= 1270 && bo->flags & XE_BO_FLAG_PAGETABLE))
 		caching = ttm_write_combined;
 
+	if (bo->flags & XE_BO_FLAG_NEEDS_UC) {
+		/*
+		 * Valid only for internally-created buffers only, for
+		 * which cpu_caching is never initialized.
+		 */
+		xe_assert(xe, bo->cpu_caching == 0);
+		caching = ttm_uncached;
+	}
+
 	err = ttm_tt_init(&tt->ttm, &bo->ttm, page_flags, caching, extra_pages);
 	if (err) {
 		kfree(tt);
-- 
2.43.0