Documentation/DMA-API-HOWTO.txt: fix misleading example

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>

1 files changed, 6 insertions, 6 deletions

diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
index d568bc235bc0..a0b6250add79 100644
--- a/Documentation/DMA-API-HOWTO.txt
+++ b/Documentation/DMA-API-HOWTO.txt
@@ -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);
                         }
                 }