This patch adds a helper function whether a queue can merge
the segments by the DMA MAP layer (e.g. via IOMMU).

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda...@renesas.com>
Reviewed-by: Christoph Hellwig <h...@lst.de>
Reviewed-by: Simon Horman <horms+rene...@verge.net.au>
---
 block/blk-settings.c   | 22 ++++++++++++++++++++++
 include/linux/blkdev.h |  2 ++
 2 files changed, 24 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 45f2c52..6a78ea0 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -4,6 +4,7 @@
  */
 #include <linux/bio.h>
 #include <linux/blkdev.h>
+#include <linux/dma-mapping.h>
 #include <linux/gcd.h>
 #include <linux/gfp.h>
 #include <linux/init.h>
@@ -831,6 +832,27 @@ void blk_queue_write_cache(struct request_queue *q, bool 
wc, bool fua)
 }
 EXPORT_SYMBOL_GPL(blk_queue_write_cache);
 
+/**
+ * blk_queue_can_use_dma_map_merging - configure queue for merging segments.
+ * @q:         the request queue for the device
+ * @dev:       the device pointer for dma
+ *
+ * Tell the block layer about merging the segments by dma map of @q.
+ */
+bool blk_queue_can_use_dma_map_merging(struct request_queue *q,
+                                      struct device *dev)
+{
+       unsigned long boundary = dma_get_merge_boundary(dev);
+
+       if (!boundary)
+               return false;
+
+       /* No need to update max_segment_size. see blk_queue_virt_boundary() */
+       blk_queue_virt_boundary(q, boundary);
+
+       return true;
+}
+
 static int __init blk_settings_init(void)
 {
        blk_max_low_pfn = max_low_pfn - 1;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ef375d..f6d55e2 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1085,6 +1085,8 @@ 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_rq_timeout(struct request_queue *, unsigned int);
 extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool 
fua);
+extern bool blk_queue_can_use_dma_map_merging(struct request_queue *q,
+                                             struct device *dev);
 
 /*
  * Number of physical segments as sent to the device.
-- 
2.7.4

Reply via email to