From: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
To: linux-kernel@vger.kernel.org
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>,
Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH] Fix DMA-API-HOWTO.txt misleading example
Date: Sun, 10 Jul 2011 13:27:10 +0200 (CEST) [thread overview]
Message-ID: <db1360f4ddad69f9a3b8bd8ed87df27d2b2919cc.1310297055.git.mirq-linux@rere.qmqm.pl> (raw)
See: DMA-API.txt, part Id, DMA_FROM_DEVICE description.
Signed-off-by: Michał Mirosław <mirq-linux@rere.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
reply other threads:[~2011-07-10 11:28 UTC|newest]
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