[PATCH] drm: round_up the size to the alignment value

[Arunpravin Paneer Selvam]

Round up the size value to the min_page_size and trim the last block to
the required size.

This solves a bug detected when size is not aligned with the min_page_size.
Unigine Heaven has allocation requests for example required pages are 257
and alignment request is 256. To allocate the left over 1 page, continues
the iteration to find the order value which is 0 and when it compares with
min_order = 8, triggers the BUG_ON(order < min_order). To avoid this issue
we round_up the size value to the min_page_size and trim the last block to
the computed required size value.

Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
---
 drivers/gpu/drm/drm_buddy.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 72f52f293249..98d7ec359b08 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -641,6 +641,7 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
 	unsigned int min_order, order;
 	unsigned long pages;
 	LIST_HEAD(allocated);
+	u64 cur_size;
 	int err;
 
 	if (size < mm->chunk_size)
@@ -665,6 +666,11 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
 	if (start + size == end)
 		return __drm_buddy_alloc_range(mm, start, size, blocks);
 
+	cur_size = size;
+
+	if (!IS_ALIGNED(size, min_page_size))
+		size = round_up(size, min_page_size);
+
 	pages = size >> ilog2(mm->chunk_size);
 	order = fls(pages) - 1;
 	min_order = ilog2(min_page_size) - ilog2(mm->chunk_size);
@@ -702,6 +708,31 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
 			break;
 	} while (1);
 
+
+	/*
+	 * If size value rounded up to min_page_size, trim the last block
+	 * to the required size
+	 */
+	if (cur_size != size) {
+		struct drm_buddy_block *trim_block;
+		LIST_HEAD(trim_list);
+		u64 required_size;
+
+		trim_block = list_last_entry(&allocated, typeof(*trim_block), link);
+		list_move_tail(&trim_block->link, &trim_list);
+		/*
+		 * Compute the required_size value by subtracting the last block size
+		 * with (aligned size - original size)
+		 */
+		required_size = drm_buddy_block_size(mm, trim_block) - (size - cur_size);
+
+		drm_buddy_block_trim(mm,
+				     required_size,
+				     &trim_list);
+
+		list_splice_tail(&trim_list, &allocated);
+	}
+
 	list_splice_tail(&allocated, blocks);
 	return 0;
 

base-commit: ec57376fba5abc0e571617ff88e2ade7970c2e4b
-- 
2.25.1