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Documentation: dmaengine: Add DMA_CTRL_REUSE documentation

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Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Acked-by:Robert Jarzmik <robert.jarzmik@free.fr>
This commit is contained in:
Vinod Koul
2015-08-05 08:42:06 +05:30
parent 06f10e2f93
commit 60884ddecd
1 changed files with 17 additions and 0 deletions
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17
Documentation/dmaengine/provider.txt
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@@ -351,6 +351,23 @@ where to put them)
- This can be acked by invoking async_tx_ack() - This can be acked by invoking async_tx_ack()
- If set, does not mean descriptor can be reused - If set, does not mean descriptor can be reused
* DMA_CTRL_REUSE
- If set, the descriptor can be reused after being completed. It should
not be freed by provider if this flag is set.
- The descriptor should be prepared for reuse by invoking
dmaengine_desc_set_reuse() which will set DMA_CTRL_REUSE.
- dmaengine_desc_set_reuse() will succeed only when channel support
reusable descriptor as exhibited by capablities
- 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.
- Descriptor can be freed in few ways
- Clearing DMA_CTRL_REUSE by invoking dmaengine_desc_clear_reuse()
and submitting for last txn
- Explicitly invoking dmaengine_desc_free(), this can succeed only
when DMA_CTRL_REUSE is already set
- Terminating the channel
General Design Notes General Design Notes
-------------------- --------------------