dmaengine: add fence support

Some engines optimize operation by reading ahead in the descriptor chain
such that descriptor2 may start execution before descriptor1 completes.
If descriptor2 depends on the result from descriptor1 then a fence is
required (on descriptor2) to disable this optimization.  The async_tx
api could implicitly identify dependencies via the 'depend_tx'
parameter, but that would constrain cases where the dependency chain
only specifies a completion order rather than a data dependency.  So,
provide an ASYNC_TX_FENCE to explicitly identify data dependencies.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 1012f1abcb54..4d6c1c925fd4 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -87,6 +87,8 @@ enum dma_transaction_type {
  * @DMA_PREP_CONTINUE - indicate to a driver that it is reusing buffers as
  *  sources that were the result of a previous operation, in the case of a PQ
  *  operation it continues the calculation with new sources
+ * @DMA_PREP_FENCE - tell the driver that subsequent operations depend
+ *  on the result of this operation
  */
 enum dma_ctrl_flags {
         DMA_PREP_INTERRUPT = (1 << 0),
@@ -98,6 +100,7 @@ enum dma_ctrl_flags {
         DMA_PREP_PQ_DISABLE_P = (1 << 6),
         DMA_PREP_PQ_DISABLE_Q = (1 << 7),
         DMA_PREP_CONTINUE = (1 << 8),
+        DMA_PREP_FENCE = (1 << 9),
 };
 
 /**