ttm: Fix caching mode selection.

A bug caused a new caching state to be selected on each buffer object
validation regardless of the current caching state.
Moreover, a caching state could be selected that wasn't supported by
the memory type.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -655,31 +655,52 @@ static int ttm_bo_mem_force_space(struct ttm_bo_device *bdev,
 	return 0;
 }
 
+static uint32_t ttm_bo_select_caching(struct ttm_mem_type_manager *man,
+				      uint32_t cur_placement,
+				      uint32_t proposed_placement)
+{
+	uint32_t caching = proposed_placement & TTM_PL_MASK_CACHING;
+	uint32_t result = proposed_placement & ~TTM_PL_MASK_CACHING;
+
+	/**
+	 * Keep current caching if possible.
+	 */
+
+	if ((cur_placement & caching) != 0)
+		result |= (cur_placement & caching);
+	else if ((man->default_caching & caching) != 0)
+		result |= man->default_caching;
+	else if ((TTM_PL_FLAG_CACHED & caching) != 0)
+		result |= TTM_PL_FLAG_CACHED;
+	else if ((TTM_PL_FLAG_WC & caching) != 0)
+		result |= TTM_PL_FLAG_WC;
+	else if ((TTM_PL_FLAG_UNCACHED & caching) != 0)
+		result |= TTM_PL_FLAG_UNCACHED;
+
+	return result;
+}
+
+
 static bool ttm_bo_mt_compatible(struct ttm_mem_type_manager *man,
 				 bool disallow_fixed,
 				 uint32_t mem_type,
-				 uint32_t mask, uint32_t *res_mask)
+				 uint32_t proposed_placement,
+				 uint32_t *masked_placement)
 {
 	uint32_t cur_flags = ttm_bo_type_flags(mem_type);
 
 	if ((man->flags & TTM_MEMTYPE_FLAG_FIXED) && disallow_fixed)
 		return false;
 
-	if ((cur_flags & mask & TTM_PL_MASK_MEM) == 0)
+	if ((cur_flags & proposed_placement & TTM_PL_MASK_MEM) == 0)
 		return false;
 
-	if ((mask & man->available_caching) == 0)
+	if ((proposed_placement & man->available_caching) == 0)
 		return false;
-	if (mask & man->default_caching)
-		cur_flags |= man->default_caching;
-	else if (mask & TTM_PL_FLAG_CACHED)
-		cur_flags |= TTM_PL_FLAG_CACHED;
-	else if (mask & TTM_PL_FLAG_WC)
-		cur_flags |= TTM_PL_FLAG_WC;
-	else
-		cur_flags |= TTM_PL_FLAG_UNCACHED;
 
-	*res_mask = cur_flags;
+	cur_flags |= (proposed_placement & man->available_caching);
+
+	*masked_placement = cur_flags;
 	return true;
 }
 
@@ -723,6 +744,9 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
 		if (!type_ok)
 			continue;
 
+		cur_flags = ttm_bo_select_caching(man, bo->mem.placement,
+						  cur_flags);
+
 		if (mem_type == TTM_PL_SYSTEM)
 			break;
 
@@ -779,6 +803,9 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
 					  proposed_placement, &cur_flags))
 			continue;
 
+		cur_flags = ttm_bo_select_caching(man, bo->mem.placement,
+						  cur_flags);
+
 		ret = ttm_bo_mem_force_space(bdev, mem, mem_type,
 					     interruptible, no_wait);