linux-kernel - [PATCH] Fix DMA-API-HOWTO.txt misleading example

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Date:	Sun, 10 Jul 2011 13:27:10 +0200 (CEST)
From:	Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:	linux-kernel@...r.kernel.org
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] Fix DMA-API-HOWTO.txt misleading example

See: DMA-API.txt, part Id, DMA_FROM_DEVICE description.

Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
---
 Documentation/DMA-API-HOWTO.txt |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/Documentation/DMA-API-HOWTO.txt b/Documentation/DMA-API-HOWTO.txt
index d568bc2..a0b6250 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);
 			}
 		}
-- 
1.7.5.4

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