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Diffstat (limited to 'Documentation/dmaengine/provider.txt')
| -rw-r--r-- | Documentation/dmaengine/provider.txt | 23 |
1 files changed, 20 insertions, 3 deletions
diff --git a/Documentation/dmaengine/provider.txt b/Documentation/dmaengine/provider.txt index ca67b0f04c6e..67d4ce4df109 100644 --- a/Documentation/dmaengine/provider.txt +++ b/Documentation/dmaengine/provider.txt @@ -345,12 +345,29 @@ where to put them) that abstracts it away. * DMA_CTRL_ACK - - 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(). + - If clear, the descriptor cannot be reused by provider until the + client acknowledges receipt, i.e. has has a chance to establish any + dependency chains + - This can be acked by invoking async_tx_ack() + - 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 -------------------- |