[PATCH 1/3] drm/xe: Add XE_BO_FLAG_SKIP_CLEAR

[Matthew Brost <matthew.brost@intel.com>]

TTM issues a GPU clear when a BO is first backed by device memory. For
BOs whose owner guarantees that every byte is either overwritten or
explicitly cleared before the contents can be observed, that clear is
pure overhead.

Add XE_BO_FLAG_SKIP_CLEAR which suppresses it. The first user is SVM
device memory, where the clear sits directly in the GPU page fault and
prefetch critical paths.

Assisted-by: Github-Copilot:Claude-opus-5
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
---
 drivers/gpu/drm/xe/xe_bo.c | 3 +++
 drivers/gpu/drm/xe/xe_bo.h | 1 +
 2 files changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index 6921b6967330..351cb12ecd11 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -1024,6 +1024,9 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
 	needs_clear = (ttm && ttm->page_flags & TTM_TT_FLAG_ZERO_ALLOC) ||
 		(!ttm && ttm_bo->type == ttm_bo_type_device);
 
+	if (bo->flags & XE_BO_FLAG_SKIP_CLEAR)
+		needs_clear = false;
+
 	if (new_mem->mem_type == XE_PL_TT) {
 		ret = xe_tt_map_sg(xe, ttm);
 		if (ret)
diff --git a/drivers/gpu/drm/xe/xe_bo.h b/drivers/gpu/drm/xe/xe_bo.h
index 861b1be231de..45fd6dea4fa7 100644
--- a/drivers/gpu/drm/xe/xe_bo.h
+++ b/drivers/gpu/drm/xe/xe_bo.h
@@ -56,6 +56,7 @@
 #define XE_BO_FLAG_FORCE_USER_VRAM	BIT(25)
 #define XE_BO_FLAG_NO_COMPRESSION	BIT(26)
 #define XE_BO_FLAG_NEEDS_1G		BIT(27)
+#define XE_BO_FLAG_SKIP_CLEAR		BIT(28)
 
 /* this one is trigger internally only */
 #define XE_BO_FLAG_INTERNAL_TEST	BIT(30)
-- 
2.34.1