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>

drivers/md/raid5.c

@@ -502,13 +502,17 @@ async_copy_data(int frombio, struct bio *bio, struct page *page,
 	int i;
 	int page_offset;
 	struct async_submit_ctl submit;
+	enum async_tx_flags flags = 0;
 
 	if (bio->bi_sector >= sector)
 		page_offset = (signed)(bio->bi_sector - sector) * 512;
 	else
 		page_offset = (signed)(sector - bio->bi_sector) * -512;
 
-	init_async_submit(&submit, 0, tx, NULL, NULL, NULL);
+	if (frombio)
+		flags |= ASYNC_TX_FENCE;
+	init_async_submit(&submit, flags, tx, NULL, NULL, NULL);
+
 	bio_for_each_segment(bvl, bio, i) {
 		int len = bio_iovec_idx(bio, i)->bv_len;
 		int clen;
@@ -685,7 +689,7 @@ ops_run_compute5(struct stripe_head *sh, struct raid5_percpu *percpu)
 
 	atomic_inc(&sh->count);
 
-	init_async_submit(&submit, ASYNC_TX_XOR_ZERO_DST, NULL,
+	init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST, NULL,
 			  ops_complete_compute, sh, to_addr_conv(sh, percpu));
 	if (unlikely(count == 1))
 		tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE, &submit);
@@ -763,7 +767,8 @@ ops_run_compute6_1(struct stripe_head *sh, struct raid5_percpu *percpu)
 		count = set_syndrome_sources(blocks, sh);
 		blocks[count] = NULL; /* regenerating p is not necessary */
 		BUG_ON(blocks[count+1] != dest); /* q should already be set */
-		init_async_submit(&submit, 0, NULL, ops_complete_compute, sh,
+		init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
+				  ops_complete_compute, sh,
 				  to_addr_conv(sh, percpu));
 		tx = async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE, &submit);
 	} else {
@@ -775,8 +780,8 @@ ops_run_compute6_1(struct stripe_head *sh, struct raid5_percpu *percpu)
 			blocks[count++] = sh->dev[i].page;
 		}
 
-		init_async_submit(&submit, ASYNC_TX_XOR_ZERO_DST, NULL,
-				  ops_complete_compute, sh,
+		init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
+				  NULL, ops_complete_compute, sh,
 				  to_addr_conv(sh, percpu));
 		tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE, &submit);
 	}
@@ -837,8 +842,9 @@ ops_run_compute6_2(struct stripe_head *sh, struct raid5_percpu *percpu)
 		/* Q disk is one of the missing disks */
 		if (faila == syndrome_disks) {
 			/* Missing P+Q, just recompute */
-			init_async_submit(&submit, 0, NULL, ops_complete_compute,
-					  sh, to_addr_conv(sh, percpu));
+			init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
+					  ops_complete_compute, sh,
+					  to_addr_conv(sh, percpu));
 			return async_gen_syndrome(blocks, 0, count+2,
 						  STRIPE_SIZE, &submit);
 		} else {
@@ -859,21 +865,24 @@ ops_run_compute6_2(struct stripe_head *sh, struct raid5_percpu *percpu)
 				blocks[count++] = sh->dev[i].page;
 			}
 			dest = sh->dev[data_target].page;
-			init_async_submit(&submit, ASYNC_TX_XOR_ZERO_DST, NULL,
-					  NULL, NULL, to_addr_conv(sh, percpu));
+			init_async_submit(&submit,
+					  ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
+					  NULL, NULL, NULL,
+					  to_addr_conv(sh, percpu));
 			tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE,
 				       &submit);
 
 			count = set_syndrome_sources(blocks, sh);
-			init_async_submit(&submit, 0, tx, ops_complete_compute,
-					  sh, to_addr_conv(sh, percpu));
+			init_async_submit(&submit, ASYNC_TX_FENCE, tx,
+					  ops_complete_compute, sh,
+					  to_addr_conv(sh, percpu));
 			return async_gen_syndrome(blocks, 0, count+2,
 						  STRIPE_SIZE, &submit);
 		}
 	}
 
-	init_async_submit(&submit, 0, NULL, ops_complete_compute, sh,
-			  to_addr_conv(sh, percpu));
+	init_async_submit(&submit, ASYNC_TX_FENCE, NULL, ops_complete_compute,
+			  sh, to_addr_conv(sh, percpu));
 	if (failb == syndrome_disks) {
 		/* We're missing D+P. */
 		return async_raid6_datap_recov(syndrome_disks+2, STRIPE_SIZE,
@@ -916,7 +925,7 @@ ops_run_prexor(struct stripe_head *sh, struct raid5_percpu *percpu,
 			xor_srcs[count++] = dev->page;
 	}
 
-	init_async_submit(&submit, ASYNC_TX_XOR_DROP_DST, tx,
+	init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
 			  ops_complete_prexor, sh, to_addr_conv(sh, percpu));
 	tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);