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>

crypto/async_tx/async_memcpy.c

@@ -52,9 +52,12 @@ async_memcpy(struct page *dest, struct page *src, unsigned int dest_offset,
 
 	if (device) {
 		dma_addr_t dma_dest, dma_src;
-		unsigned long dma_prep_flags;
+		unsigned long dma_prep_flags = 0;
 
-		dma_prep_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
+		if (submit->cb_fn)
+			dma_prep_flags |= DMA_PREP_INTERRUPT;
+		if (submit->flags & ASYNC_TX_FENCE)
+			dma_prep_flags |= DMA_PREP_FENCE;
 		dma_dest = dma_map_page(device->dev, dest, dest_offset, len,
 					DMA_FROM_DEVICE);
 

crypto/async_tx/async_memset.c

@@ -49,9 +49,12 @@ async_memset(struct page *dest, int val, unsigned int offset, size_t len,
 
 	if (device) {
 		dma_addr_t dma_dest;
-		unsigned long dma_prep_flags;
+		unsigned long dma_prep_flags = 0;
 
-		dma_prep_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
+		if (submit->cb_fn)
+			dma_prep_flags |= DMA_PREP_INTERRUPT;
+		if (submit->flags & ASYNC_TX_FENCE)
+			dma_prep_flags |= DMA_PREP_FENCE;
 		dma_dest = dma_map_page(device->dev, dest, offset, len,
 					DMA_FROM_DEVICE);
 

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]));

crypto/async_tx/async_raid6_recov.c

@@ -44,6 +44,8 @@ async_sum_product(struct page *dest, struct page **srcs, unsigned char *coef,
 		struct dma_async_tx_descriptor *tx;
 		enum dma_ctrl_flags dma_flags = DMA_PREP_PQ_DISABLE_P;
 
+		if (submit->flags & ASYNC_TX_FENCE)
+			dma_flags |= DMA_PREP_FENCE;
 		dma_dest[1] = dma_map_page(dev, dest, 0, len, DMA_BIDIRECTIONAL);
 		dma_src[0] = dma_map_page(dev, srcs[0], 0, len, DMA_TO_DEVICE);
 		dma_src[1] = dma_map_page(dev, srcs[1], 0, len, DMA_TO_DEVICE);
@@ -89,6 +91,8 @@ async_mult(struct page *dest, struct page *src, u8 coef, size_t len,
 		struct dma_async_tx_descriptor *tx;
 		enum dma_ctrl_flags dma_flags = DMA_PREP_PQ_DISABLE_P;
 
+		if (submit->flags & ASYNC_TX_FENCE)
+			dma_flags |= DMA_PREP_FENCE;
 		dma_dest[1] = dma_map_page(dev, dest, 0, len, DMA_BIDIRECTIONAL);
 		dma_src[0] = dma_map_page(dev, src, 0, len, DMA_TO_DEVICE);
 		tx = dma->device_prep_dma_pq(chan, dma_dest, dma_src, 1, &coef,
@@ -138,7 +142,7 @@ __2data_recov_4(size_t bytes, int faila, int failb, struct page **blocks,
 	srcs[1] = q;
 	coef[0] = raid6_gfexi[failb-faila];
 	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
-	init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_sum_product(b, srcs, coef, bytes, submit);
 
 	/* Dy = P+Pxy+Dx */
@@ -188,23 +192,23 @@ __2data_recov_5(size_t bytes, int faila, int failb, struct page **blocks,
 	dp = blocks[faila];
 	dq = blocks[failb];
 
-	init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_memcpy(dp, g, 0, 0, bytes, submit);
-	init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_mult(dq, g, raid6_gfexp[good], bytes, submit);
 
 	/* compute P + Pxy */
 	srcs[0] = dp;
 	srcs[1] = p;
-	init_async_submit(submit, ASYNC_TX_XOR_DROP_DST, tx, NULL, NULL,
-			  scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
+			  NULL, NULL, scribble);
 	tx = async_xor(dp, srcs, 0, 2, bytes, submit);
 
 	/* compute Q + Qxy */
 	srcs[0] = dq;
 	srcs[1] = q;
-	init_async_submit(submit, ASYNC_TX_XOR_DROP_DST, tx, NULL, NULL,
-			  scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
+			  NULL, NULL, scribble);
 	tx = async_xor(dq, srcs, 0, 2, bytes, submit);
 
 	/* Dx = A*(P+Pxy) + B*(Q+Qxy) */
@@ -212,7 +216,7 @@ __2data_recov_5(size_t bytes, int faila, int failb, struct page **blocks,
 	srcs[1] = dq;
 	coef[0] = raid6_gfexi[failb-faila];
 	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
-	init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_sum_product(dq, srcs, coef, bytes, submit);
 
 	/* Dy = P+Pxy+Dx */
@@ -252,7 +256,7 @@ __2data_recov_n(int disks, size_t bytes, int faila, int failb,
 	blocks[failb] = (void *)raid6_empty_zero_page;
 	blocks[disks-1] = dq;
 
-	init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_gen_syndrome(blocks, 0, disks, bytes, submit);
 
 	/* Restore pointer table */
@@ -264,15 +268,15 @@ __2data_recov_n(int disks, size_t bytes, int faila, int failb,
 	/* compute P + Pxy */
 	srcs[0] = dp;
 	srcs[1] = p;
-	init_async_submit(submit, ASYNC_TX_XOR_DROP_DST, tx, NULL, NULL,
-			  scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
+			  NULL, NULL, scribble);
 	tx = async_xor(dp, srcs, 0, 2, bytes, submit);
 
 	/* compute Q + Qxy */
 	srcs[0] = dq;
 	srcs[1] = q;
-	init_async_submit(submit, ASYNC_TX_XOR_DROP_DST, tx, NULL, NULL,
-			  scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
+			  NULL, NULL, scribble);
 	tx = async_xor(dq, srcs, 0, 2, bytes, submit);
 
 	/* Dx = A*(P+Pxy) + B*(Q+Qxy) */
@@ -280,7 +284,7 @@ __2data_recov_n(int disks, size_t bytes, int faila, int failb,
 	srcs[1] = dq;
 	coef[0] = raid6_gfexi[failb-faila];
 	coef[1] = raid6_gfinv[raid6_gfexp[faila]^raid6_gfexp[failb]];
-	init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_sum_product(dq, srcs, coef, bytes, submit);
 
 	/* Dy = P+Pxy+Dx */
@@ -407,13 +411,16 @@ async_raid6_datap_recov(int disks, size_t bytes, int faila,
 		int good = faila == 0 ? 1 : 0;
 		struct page *g = blocks[good];
 
-		init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+		init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
+				  scribble);
 		tx = async_memcpy(p, g, 0, 0, bytes, submit);
 
-		init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+		init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
+				  scribble);
 		tx = async_mult(dq, g, raid6_gfexp[good], bytes, submit);
 	} else {
-		init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+		init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL,
+				  scribble);
 		tx = async_gen_syndrome(blocks, 0, disks, bytes, submit);
 	}
 
@@ -426,11 +433,11 @@ async_raid6_datap_recov(int disks, size_t bytes, int faila,
 
 	srcs[0] = dq;
 	srcs[1] = q;
-	init_async_submit(submit, ASYNC_TX_XOR_DROP_DST, tx, NULL, NULL,
-			  scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
+			  NULL, NULL, scribble);
 	tx = async_xor(dq, srcs, 0, 2, bytes, submit);
 
-	init_async_submit(submit, 0, tx, NULL, NULL, scribble);
+	init_async_submit(submit, ASYNC_TX_FENCE, tx, NULL, NULL, scribble);
 	tx = async_mult(dq, dq, coef, bytes, submit);
 
 	srcs[0] = p;

crypto/async_tx/async_xor.c

@@ -69,6 +69,7 @@ do_async_xor(struct dma_chan *chan, struct page *dest, struct page **src_list,
 		 */
 		if (src_cnt > xor_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;
@@ -78,7 +79,8 @@ do_async_xor(struct dma_chan *chan, struct page *dest, struct page **src_list,
 		}
 		if (submit->cb_fn)
 			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 progress
 		 * in case they can not provide a descriptor
@@ -264,12 +266,15 @@ async_xor_val(struct page *dest, struct page **src_list, unsigned int offset,
 		dma_src = (dma_addr_t *) src_list;
 
 	if (dma_src && device && src_cnt <= device->max_xor) {
-		unsigned long dma_prep_flags;
+		unsigned long dma_prep_flags = 0;
 		int i;
 
 		pr_debug("%s: (async) len: %zu\n", __func__, len);
 
-		dma_prep_flags = submit->cb_fn ? DMA_PREP_INTERRUPT : 0;
+		if (submit->cb_fn)
+			dma_prep_flags |= DMA_PREP_INTERRUPT;
+		if (submit->flags & ASYNC_TX_FENCE)
+			dma_prep_flags |= DMA_PREP_FENCE;
 		for (i = 0; i < src_cnt; i++)
 			dma_src[i] = dma_map_page(device->dev, src_list[i],
 						  offset, len, DMA_TO_DEVICE);

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);
 

include/linux/async_tx.h

@@ -58,11 +58,14 @@ struct dma_chan_ref {
  * array.
  * @ASYNC_TX_ACK: immediately ack the descriptor, precludes setting up a
  * dependency chain
+ * @ASYNC_TX_FENCE: specify that the next operation in the dependency
+ * chain uses this operation's result as an input
  */
 enum async_tx_flags {
 	ASYNC_TX_XOR_ZERO_DST	 = (1 << 0),
 	ASYNC_TX_XOR_DROP_DST	 = (1 << 1),
 	ASYNC_TX_ACK		 = (1 << 2),
+	ASYNC_TX_FENCE		 = (1 << 3),
 };
 
 /**

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),
 };
 
 /**