drm/xe: Perform dma_map when moving system buffer objects to TT

Currently we dma_map on ttm_tt population and dma_unmap when
the pages are released in ttm_tt unpopulate.

Strictly, the dma_map is not needed until the bo is moved to the
XE_PL_TT placement, so perform the dma_mapping on such moves
instead, and remove the dma_mappig when moving to XE_PL_SYSTEM.

This is desired for the upcoming shrinker series where shrinking
of a ttm_tt might fail. That would lead to an odd construct where
we first dma_unmap, then shrink and if shrinking fails dma_map
again. If dma_mapping instead is performed on move like this,
shrinking does not need to care at all about dma mapping.

Finally, where a ttm_tt is destroyed while bound to a different
memory type than XE_PL_SYSTEM, we keep the dma_unmap in
unpopulate().

v2:
- Don't accidently unmap the dma-buf's sgtable.

Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240502183251.10170-1-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/xe/xe_bo.c

@@ -302,6 +302,18 @@ static int xe_tt_map_sg(struct ttm_tt *tt)
 	return 0;
 }
 
+static void xe_tt_unmap_sg(struct ttm_tt *tt)
+{
+	struct xe_ttm_tt *xe_tt = container_of(tt, struct xe_ttm_tt, ttm);
+
+	if (xe_tt->sg) {
+		dma_unmap_sgtable(xe_tt->dev, xe_tt->sg,
+				  DMA_BIDIRECTIONAL, 0);
+		sg_free_table(xe_tt->sg);
+		xe_tt->sg = NULL;
+	}
+}
+
 struct sg_table *xe_bo_sg(struct xe_bo *bo)
 {
 	struct ttm_tt *tt = bo->ttm.ttm;
@@ -377,27 +389,15 @@ static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct ttm_tt *tt,
 	if (err)
 		return err;
 
-	/* A follow up may move this xe_bo_move when BO is moved to XE_PL_TT */
-	err = xe_tt_map_sg(tt);
-	if (err)
-		ttm_pool_free(&ttm_dev->pool, tt);
-
 	return err;
 }
 
 static void xe_ttm_tt_unpopulate(struct ttm_device *ttm_dev, struct ttm_tt *tt)
 {
-	struct xe_ttm_tt *xe_tt = container_of(tt, struct xe_ttm_tt, ttm);
-
 	if (tt->page_flags & TTM_TT_FLAG_EXTERNAL)
 		return;
 
-	if (xe_tt->sg) {
+	xe_tt_unmap_sg(tt);
-		dma_unmap_sgtable(xe_tt->dev, xe_tt->sg,
-				  DMA_BIDIRECTIONAL, 0);
-		sg_free_table(xe_tt->sg);
-		xe_tt->sg = NULL;
-	}
 
 	return ttm_pool_free(&ttm_dev->pool, tt);
 }
@@ -628,17 +628,21 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
 	bool handle_system_ccs = (!IS_DGFX(xe) && xe_bo_needs_ccs_pages(bo) &&
 				  ttm && ttm_tt_is_populated(ttm)) ? true : false;
 	int ret = 0;
+
 	/* Bo creation path, moving to system or TT. */
 	if ((!old_mem && ttm) && !handle_system_ccs) {
-		ttm_bo_move_null(ttm_bo, new_mem);
+		if (new_mem->mem_type == XE_PL_TT)
-		return 0;
+			ret = xe_tt_map_sg(ttm);
+		if (!ret)
+			ttm_bo_move_null(ttm_bo, new_mem);
+		goto out;
 	}
 
 	if (ttm_bo->type == ttm_bo_type_sg) {
 		ret = xe_bo_move_notify(bo, ctx);
 		if (!ret)
 			ret = xe_bo_move_dmabuf(ttm_bo, new_mem);
-		goto out;
+		return ret;
 	}
 
 	tt_has_data = ttm && (ttm_tt_is_populated(ttm) ||
@@ -650,6 +654,12 @@ 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 (new_mem->mem_type == XE_PL_TT) {
+		ret = xe_tt_map_sg(ttm);
+		if (ret)
+			goto out;
+	}
+
 	if ((move_lacks_source && !needs_clear)) {
 		ttm_bo_move_null(ttm_bo, new_mem);
 		goto out;
@@ -786,8 +796,11 @@ static int xe_bo_move(struct ttm_buffer_object *ttm_bo, bool evict,
 	xe_pm_runtime_put(xe);
 
 out:
-	return ret;
+	if ((!ttm_bo->resource || ttm_bo->resource->mem_type == XE_PL_SYSTEM) &&
+	    ttm_bo->ttm)
+		xe_tt_unmap_sg(ttm_bo->ttm);
 
+	return ret;
 }
 
 /**