[PATCH 5/8] drm: Implement method to free unused pages

[Arunpravin]

On contiguous allocation, we round up the size
to the *next* power of 2, implement a function
to free the unused pages after the newly allocate block.

Signed-off-by: Arunpravin <Arunpravin.PaneerSelvam at amd.com>
---
 drivers/gpu/drm/drm_buddy.c | 103 ++++++++++++++++++++++++++++++++++++
 include/drm/drm_buddy.h     |   4 ++
 2 files changed, 107 insertions(+)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 9d3547bcc5da..0da8510736eb 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -284,6 +284,109 @@ static inline bool contains(u64 s1, u64 e1, u64 s2, u64 e2)
 	return s1 <= s2 && e1 >= e2;
 }
 
+/**
+ * drm_buddy_free_unused_pages - free unused pages
+ *
+ * @mm: DRM buddy manager
+ * @actual_size: original size requested
+ * @blocks: output list head to add allocated blocks
+ *
+ * For contiguous allocation, we round up the size to the nearest
+ * power of two value, drivers consume *actual* size, so remaining
+ * portions are unused and it can be freed.
+ *
+ * Returns:
+ * 0 on success, error code on failure.
+ */
+int drm_buddy_free_unused_pages(struct drm_buddy_mm *mm,
+				u64 actual_size,
+				struct list_head *blocks)
+{
+	struct drm_buddy_block *block;
+	struct drm_buddy_block *buddy;
+	u64 actual_start;
+	u64 actual_end;
+	LIST_HEAD(dfs);
+	u64 count = 0;
+	int err;
+
+	if (!list_is_singular(blocks))
+		return -EINVAL;
+
+	block = list_first_entry_or_null(blocks,
+					 struct drm_buddy_block,
+					 link);
+
+	if (!block)
+		return -EINVAL;
+
+	if (actual_size > drm_buddy_block_size(mm, block))
+		return -EINVAL;
+
+	if (actual_size == drm_buddy_block_size(mm, block))
+		return 0;
+
+	list_del(&block->link);
+
+	actual_start = drm_buddy_block_offset(block);
+	actual_end = actual_start + actual_size - 1;
+
+	if (drm_buddy_block_is_allocated(block))
+		mark_free(mm, block);
+
+	list_add(&block->tmp_link, &dfs);
+
+	while (1) {
+		block = list_first_entry_or_null(&dfs,
+						 struct drm_buddy_block,
+						 tmp_link);
+
+		if (!block)
+			break;
+
+		list_del(&block->tmp_link);
+
+		if (count == actual_size)
+			return 0;
+
+		if (contains(actual_start, actual_end, drm_buddy_block_offset(block),
+			(drm_buddy_block_offset(block) + drm_buddy_block_size(mm, block) - 1))) {
+			BUG_ON(!drm_buddy_block_is_free(block));
+
+			/* Allocate only required blocks */
+			mark_allocated(block);
+			mm->avail -= drm_buddy_block_size(mm, block);
+			list_add_tail(&block->link, blocks);
+			count += drm_buddy_block_size(mm, block);
+			continue;
+		}
+
+		if (drm_buddy_block_order(block) == 0)
+			continue;
+
+		if (!drm_buddy_block_is_split(block)) {
+			err = split_block(mm, block);
+
+			if (unlikely(err))
+				goto err_undo;
+		}
+
+		list_add(&block->right->tmp_link, &dfs);
+		list_add(&block->left->tmp_link, &dfs);
+	}
+
+	return -ENOSPC;
+
+err_undo:
+	buddy = get_buddy(block);
+	if (buddy &&
+	    (drm_buddy_block_is_free(block) &&
+	     drm_buddy_block_is_free(buddy)))
+		__drm_buddy_free(mm, block);
+	return err;
+}
+EXPORT_SYMBOL(drm_buddy_free_unused_pages);
+
 static struct drm_buddy_block *
 alloc_range(struct drm_buddy_mm *mm,
 	    u64 start, u64 end,
diff --git a/include/drm/drm_buddy.h b/include/drm/drm_buddy.h
index cd8021d2d6e7..1dfc80c88e1f 100644
--- a/include/drm/drm_buddy.h
+++ b/include/drm/drm_buddy.h
@@ -145,6 +145,10 @@ int drm_buddy_alloc(struct drm_buddy_mm *mm,
 		    struct list_head *blocks,
 		    unsigned long flags);
 
+int drm_buddy_free_unused_pages(struct drm_buddy_mm *mm,
+				u64 actual_size,
+				struct list_head *blocks);
+
 void drm_buddy_free(struct drm_buddy_mm *mm, struct drm_buddy_block *block);
 
 void drm_buddy_free_list(struct drm_buddy_mm *mm, struct list_head *objects);
-- 
2.25.1