drm/buddy: Add start address support to trim function

- Add a new start parameter in trim function to specify exact
address from where to start the trimming. This would help us
in situations like if drivers would like to do address alignment
for specific requirements.

- Add a new flag DRM_BUDDY_TRIM_DISABLE. Drivers can use this
flag to disable the allocator trimming part. This patch enables
the drivers control trimming and they can do it themselves
based on the application requirements.

v1:(Matthew)
- check new_start alignment with min chunk_size
- use range_overflows()

Signed-off-by: Arunpravin Paneer Selvam <[e-mail]>
Acked-by: Alex Deucher <[e-mail]>
Acked-by: Christian König <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>
(cherry picked from commit db65eb46de135338d6177f8853e0fd208f19d63e)

drivers/gpu/drm/drm_buddy.c

···
  * drm_buddy_block_trim - free unused pages
  *
  * @mm: DRM buddy manager
+ * @start: start address to begin the trimming.
  * @new_size: original size requested
  * @blocks: Input and output list of allocated blocks.
  * MUST contain single block as input to be trimmed.
···
  * 0 on success, error code on failure.
  */
 int drm_buddy_block_trim(struct drm_buddy *mm,
+			 u64 *start,
 			 u64 new_size,
 			 struct list_head *blocks)
 {
 	struct drm_buddy_block *parent;
 	struct drm_buddy_block *block;
+	u64 block_start, block_end;
 	LIST_HEAD(dfs);
 	u64 new_start;
 	int err;
···
 	block = list_first_entry(blocks,
 				 struct drm_buddy_block,
 				 link);
+
+	block_start = drm_buddy_block_offset(block);
+	block_end = block_start + drm_buddy_block_size(mm, block);
 
 	if (WARN_ON(!drm_buddy_block_is_allocated(block)))
 		return -EINVAL;
···
 	if (new_size == drm_buddy_block_size(mm, block))
 		return 0;
 
+	new_start = block_start;
+	if (start) {
+		new_start = *start;
+
+		if (new_start < block_start)
+			return -EINVAL;
+
+		if (!IS_ALIGNED(new_start, mm->chunk_size))
+			return -EINVAL;
+
+		if (range_overflows(new_start, new_size, block_end))
+			return -EINVAL;
+	}
+
 	list_del(&block->link);
 	mark_free(mm, block);
 	mm->avail += drm_buddy_block_size(mm, block);
···
 	parent = block->parent;
 	block->parent = NULL;
 
-	new_start = drm_buddy_block_offset(block);
 	list_add(&block->tmp_link, &dfs);
 	err =  __alloc_range(mm, &dfs, new_start, new_size, blocks, NULL);
 	if (err) {
···
 	} while (1);
 
 	/* Trim the allocated block to the required size */
-	if (original_size != size) {
+	if (!(flags & DRM_BUDDY_TRIM_DISABLE) &&
+	    original_size != size) {
 		struct list_head *trim_list;
 		LIST_HEAD(temp);
 		u64 trim_size;
···
 		}
 
 		drm_buddy_block_trim(mm,
+				     NULL,
 				     trim_size,
 				     trim_list);
 

drivers/gpu/drm/xe/xe_ttm_vram_mgr.c

···
 	} while (remaining_size);
 
 	if (place->flags & TTM_PL_FLAG_CONTIGUOUS) {
-		if (!drm_buddy_block_trim(mm, vres->base.size, &vres->blocks))
+		if (!drm_buddy_block_trim(mm, NULL, vres->base.size, &vres->blocks))
 			size = vres->base.size;
 	}
 

include/drm/drm_buddy.h

···
 #define DRM_BUDDY_CONTIGUOUS_ALLOCATION		BIT(2)
 #define DRM_BUDDY_CLEAR_ALLOCATION		BIT(3)
 #define DRM_BUDDY_CLEARED			BIT(4)
+#define DRM_BUDDY_TRIM_DISABLE			BIT(5)
 
 struct drm_buddy_block {
 #define DRM_BUDDY_HEADER_OFFSET GENMASK_ULL(63, 12)
···
 			   unsigned long flags);
 
 int drm_buddy_block_trim(struct drm_buddy *mm,
+			 u64 *start,
 			 u64 new_size,
 			 struct list_head *blocks);