[ARM] Don't call consistent_sync() for DMA coherent memory

Memory allocated by the coherent memory allocators will be marked
uncacheable, which means it's pointless calling consistent_sync()
to perform cache maintainence on this memory; it's just a waste of
CPU cycles.

Moreover, with the (subsequent) merge of outer cache support, it
actually breaks things to call consistent_sync() on anything but
direct-mapped memory.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 10 insertions, 3 deletions

diff --git a/arch/arm/common/dmabounce.c b/arch/arm/common/dmabounce.c
index 2e635b814c14..272702accd8b 100644
--- a/arch/arm/common/dmabounce.c
+++ b/arch/arm/common/dmabounce.c
@@ -281,10 +281,14 @@ map_single(struct device *dev, void *ptr, size_t size,
                 ptr = buf->safe;
 
                 dma_addr = buf->safe_dma_addr;
+        } else {
+                /*
+                 * We don't need to sync the DMA buffer since
+                 * it was allocated via the coherent allocators.
+                 */
+                consistent_sync(ptr, size, dir);
         }
 
-        consistent_sync(ptr, size, dir);
-
         return dma_addr;
 }
 
@@ -397,7 +401,10 @@ sync_single(struct device *dev, dma_addr_t dma_addr, size_t size,
                 default:
                         BUG();
                 }
-                consistent_sync(buf->safe, size, dir);
+                /*
+                 * No need to sync the safe buffer - it was allocated
+                 * via the coherent allocators.
+                 */
         } else {
                 consistent_sync(dma_to_virt(dev, dma_addr), size, dir);
         }