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Diffstat (limited to 'Documentation/dmaengine')
| -rw-r--r-- | Documentation/dmaengine/provider.txt | 17 |
1 files changed, 17 insertions, 0 deletions
diff --git a/Documentation/dmaengine/provider.txt b/Documentation/dmaengine/provider.txt index 243889ec5c5a..67d4ce4df109 100644 --- a/Documentation/dmaengine/provider.txt +++ b/Documentation/dmaengine/provider.txt @@ -351,6 +351,23 @@ where to put them) - 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 -------------------- |