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, 5 insertions, 0 deletions

diff --git a/crypto/async_tx/async_pq.c b/crypto/async_tx/async_pq.c
index 108b21efb499..a25e290c39fb 100644
--- a/crypto/async_tx/async_pq.c
+++ b/crypto/async_tx/async_pq.c
@@ -101,6 +101,7 @@ do_async_gen_syndrome(struct dma_chan *chan, struct page **blocks,
                  */
                 if (src_cnt > pq_src_cnt) {
                         submit->flags &= ~ASYNC_TX_ACK;
+                        submit->flags |= ASYNC_TX_FENCE;
                         dma_flags |= DMA_COMPL_SKIP_DEST_UNMAP;
                         submit->cb_fn = NULL;
                         submit->cb_param = NULL;
@@ -111,6 +112,8 @@ do_async_gen_syndrome(struct dma_chan *chan, struct page **blocks,
                         if (cb_fn_orig)
                                 dma_flags |= DMA_PREP_INTERRUPT;
                 }
+                if (submit->flags & ASYNC_TX_FENCE)
+                        dma_flags |= DMA_PREP_FENCE;
 
                 /* Since we have clobbered the src_list we are committed
                  * to doing this asynchronously.  Drivers force forward
@@ -282,6 +285,8 @@ async_syndrome_val(struct page **blocks, unsigned int offset, int disks,
                         dma_flags |= DMA_PREP_PQ_DISABLE_P;
                 if (!Q(blocks, disks))
                         dma_flags |= DMA_PREP_PQ_DISABLE_Q;
+                if (submit->flags & ASYNC_TX_FENCE)
+                        dma_flags |= DMA_PREP_FENCE;
                 for (i = 0; i < disks; i++)
                         if (likely(blocks[i])) {
                                 BUG_ON(is_raid6_zero_block(blocks[i]));