There is no need to perform full BIDIR sync (copying the buffers in case

of swiotlb and similar schemes) if we know that the owner (CPU or device)
hasn't altered the data.

Addresses the false-positive reported at
http://bugzilla.kernel.org/show_bug.cgi?id=14169Signed-off-by: Krzysztof Halasa <khc@pm.waw.pl>
Cc: David Miller <davem@davemloft.net>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/dma-debug.c

@@ -907,6 +907,9 @@ static void check_sync(struct device *dev,
 				ref->size);
 	}
 
+	if (entry->direction == DMA_BIDIRECTIONAL)
+		goto out;
+
 	if (ref->direction != entry->direction) {
 		err_printk(dev, entry, "DMA-API: device driver syncs "
 				"DMA memory with different direction "
@@ -917,9 +920,6 @@ static void check_sync(struct device *dev,
 				dir2name[ref->direction]);
 	}
 
-	if (entry->direction == DMA_BIDIRECTIONAL)
-		goto out;
-
 	if (to_cpu && !(entry->direction == DMA_FROM_DEVICE) &&
 		      !(ref->direction == DMA_TO_DEVICE))
 		err_printk(dev, entry, "DMA-API: device driver syncs "
@@ -942,7 +942,6 @@ static void check_sync(struct device *dev,
 
 out:
 	put_hash_bucket(bucket, &flags);
-
 }
 
 void debug_dma_map_page(struct device *dev, struct page *page, size_t offset,