Documentation: dmaengine: Add DMA_CTRL_REUSE documentation
Signed-off-by: Vinod Koul <vinod.koul@intel.com>
Acked-by:Robert Jarzmik <robert.jarzmik@free.fr>
diff --git a/Documentation/dmaengine/provider.txt b/Documentation/dmaengine/provider.txt
index 243889e..67d4ce4 100644
--- a/Documentation/dmaengine/provider.txt
+++ b/Documentation/dmaengine/provider.txt
@@ -351,6 +351,23 @@
- 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
--------------------