dma-debug: allow DMA_BIDIRECTIONAL mappings to be synced with DMA_FROM_DEVICE and

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=14169

Signed-off-by: Krzysztof Halasa <khc@pm.waw.pl>
Cc: David Miller <davem@davemloft.net>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/dma-debug.c

@@ -913,6 +913,9 @@ 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 "
@@ -923,9 +926,6 @@ 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 "
@@ -948,7 +948,6 @@ 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,