2 files changed, 25 insertions, 0 deletions

diff --git a/block/ll_rw_blk.c b/block/ll_rw_blk.c
index 8b919940b2ab..14af36c5cdb2 100644
--- a/block/ll_rw_blk.c
+++ b/block/ll_rw_blk.c
@@ -760,6 +760,30 @@ void blk_queue_dma_alignment(struct request_queue *q, int mask)
 EXPORT_SYMBOL(blk_queue_dma_alignment);
 
 /**
+ * blk_queue_update_dma_alignment - update dma length and memory alignment
+ * @q:     the request queue for the device
+ * @mask:  alignment mask
+ *
+ * description:
+ *    update required memory and length aligment for direct dma transactions.
+ *    If the requested alignment is larger than the current alignment, then
+ *    the current queue alignment is updated to the new value, otherwise it
+ *    is left alone.  The design of this is to allow multiple objects
+ *    (driver, device, transport etc) to set their respective
+ *    alignments without having them interfere.
+ *
+ **/
+void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
+{
+        BUG_ON(mask > PAGE_SIZE);
+
+        if (mask > q->dma_alignment)
+                q->dma_alignment = mask;
+}
+
+EXPORT_SYMBOL(blk_queue_update_dma_alignment);
+
+/**
  * blk_queue_find_tag - find a request by its tag and queue
  * @q:   The request queue for the device
  * @tag: The tag of the request
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d18ee67b40f8..81e99e516302 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -766,6 +766,7 @@ extern void blk_queue_segment_boundary(struct request_queue *, unsigned long);
 extern void blk_queue_prep_rq(struct request_queue *, prep_rq_fn *pfn);
 extern void blk_queue_merge_bvec(struct request_queue *, merge_bvec_fn *);
 extern void blk_queue_dma_alignment(struct request_queue *, int);
+extern void blk_queue_update_dma_alignment(struct request_queue *, int);
 extern void blk_queue_softirq_done(struct request_queue *, softirq_done_fn *);
 extern struct backing_dev_info *blk_get_backing_dev_info(struct block_device *bdev);
 extern int blk_queue_ordered(struct request_queue *, unsigned, prepare_flush_fn *);