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Documentation: dmaengine: document DMA_CTRL_ACK

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Add documentation about acking the transfers, and their
reusability.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
This commit is contained in:
Robert Jarzmik 2015-05-26 23:06:34 +02:00 committed by Vinod Koul
parent b9855f03d5
commit 5f88d9706f
1 changed files with 6 additions and 5 deletions
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11
Documentation/dmaengine/provider.txt
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@ -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
--------------------