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-rw-r--r--Documentation/dmaengine/provider.txt11
1 files changed, 6 insertions, 5 deletions
diff --git a/Documentation/dmaengine/provider.txt b/Documentation/dmaengine/provider.txt
index 05d228019..ca67b0f04 100644
--- a/Documentation/dmaengine/provider.txt
+++ b/Documentation/dmaengine/provider.txt
@@ -345,11 +345,12 @@ where to put them)
that abstracts it away.
* DMA_CTRL_ACK
- - Undocumented feature
- - No one really has an idea of what it's about, besides being
- related to reusing the DMA transaction descriptors or having
- additional transactions added to it in the async-tx API
- - Useless in the case of the slave API
+ - If set, the transfer can be reused after being completed.
+ - There is a guarantee the transfer won't be freed until it is acked
+ by async_tx_ack().
+ - As a consequence, if a device driver wants to skip the dma_map_sg() and
+ dma_unmap_sg() in between 2 transfers, because the DMA'd data wasn't used,
+ it can resubmit the transfer right after its completion.
General Design Notes
--------------------