Documentation/DMA-API-HOWTO.txt: fix misleading example
Michal Miroslaw [Tue, 26 Jul 2011 23:08:51 +0000 (16:08 -0700)]
See: DMA-API.txt, part Id, DMA_FROM_DEVICE description.

Signed-off-by: Michal Miroslaw <mirq-linux@rere.qmqm.pl>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/DMA-API-HOWTO.txt

index d568bc2..a0b6250 100644 (file)
@@ -613,13 +613,13 @@ to use the dma_sync_*() interfaces.
                                pass_to_upper_layers(cp->rx_buf);
                                make_and_setup_new_rx_buf(cp);
                        } else {
-                               /* Just sync the buffer and give it back
-                                * to the card.
+                               /* CPU should not write to
+                                * DMA_FROM_DEVICE-mapped area,
+                                * so dma_sync_single_for_device() is
+                                * not needed here. It would be required
+                                * for DMA_BIDIRECTIONAL mapping if
+                                * the memory was modified.
                                 */
-                               dma_sync_single_for_device(&cp->dev,
-                                                          cp->rx_dma,
-                                                          cp->rx_len,
-                                                          DMA_FROM_DEVICE);
                                give_rx_buf_to_card(cp);
                        }
                }