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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>
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commit 3f0fb4e85b3842a2606c647c0a66afe2073574b4 1 parent 91f6cdf
Michal Miroslaw authored torvalds committed
Showing with 6 additions and 6 deletions.
  1. +6 −6 Documentation/DMA-API-HOWTO.txt
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12 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);
}
}
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