dma-debug: allow DMA_BIDIRECTIONAL mappings to be synced with DMA_FRO…

…M_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 <[email protected]>
Cc: David Miller <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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,