[PATCH v5 06/10] dmaengine: dw: simplify transfer-complete handling

[James Hilliard]

With hardware-LLP residue handled by the status getter, the descriptor
scanner only needs to process transfer-complete events. Return through a
common unlock path when no event or active descriptor remains, and flatten
the completion handling.

Only one transaction is active on a channel. Detach that descriptor before
starting the next queued transfer, keeping cookie completion under the
channel lock and client notification outside it. Preserve software-LLP
block advancement before completing the transaction.

Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>

---

Changelog RFC:
- Instead of just dropping the dwc_scan_descriptors() method invocation
  calculate the residue in the Tx-status getter.
---
 drivers/dma/dw/core.c | 92 +++++++++++++++++++++------------------------------
 1 file changed, 38 insertions(+), 54 deletions(-)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 0d6b5bd8ea6b..e198c9f45f0b 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -271,74 +271,58 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
 {
 	struct dw_desc *desc, *_desc;
 	struct dw_desc *child;
-	u32 status_xfer;
 	unsigned long flags;
 	LIST_HEAD(list);
 
 	spin_lock_irqsave(&dwc->lock, flags);
-	status_xfer = dma_readl(dw, RAW.XFER);
-
-	if (status_xfer & dwc->mask) {
-		/* Everything we've submitted is done */
-		dma_writel(dw, CLEAR.XFER, dwc->mask);
-		if (list_empty(&dwc->active_list)) {
-			spin_unlock_irqrestore(&dwc->lock, flags);
-			return;
-		}
-
-		if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
-			struct list_head *head, *active = dwc->tx_node_active;
-
-			/*
-			 * We are inside first active descriptor.
-			 * Otherwise something is really wrong.
-			 */
-			desc = dwc_first_active(dwc);
-
-			head = &desc->tx_list;
-			if (active != head) {
-				/* Update residue to reflect last sent descriptor */
-				if (active == head->next)
-					desc->residue -= desc->len;
-				else
-					desc->residue -= to_dw_desc(active->prev)->len;
 
-				child = to_dw_desc(active);
-
-				/* Submit next block */
-				dwc_do_single_block(dwc, child);
+	if (!(dma_readl(dw, RAW.XFER) & dwc->mask))
+		goto unlock;
 
-				spin_unlock_irqrestore(&dwc->lock, flags);
-				return;
-			}
+	dma_writel(dw, CLEAR.XFER, dwc->mask);
+	if (list_empty(&dwc->active_list))
+		goto unlock;
 
-			/* We are done here */
-			clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
+	desc = dwc_first_active(dwc);
+	if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
+		struct list_head *head = &desc->tx_list;
+		struct list_head *active = dwc->tx_node_active;
+
+		if (active != head) {
+			/* Update residue to reflect last sent descriptor. */
+			if (active == head->next)
+				desc->residue -= desc->len;
+			else
+				desc->residue -= to_dw_desc(active->prev)->len;
+
+			child = to_dw_desc(active);
+
+			/* Submit next block, including for polled transfers. */
+			dwc_do_single_block(dwc, child);
+			goto unlock;
 		}
 
-		if (dma_readl(dw, CH_EN) & dwc->mask) {
-			dev_err(dmaengine_chan_dev(&dwc->chan),
-				"BUG: XFER bit set, but channel not idle!\n");
-
-			/* Try to continue after resetting the channel... */
-			dwc_chan_disable(dw, dwc);
-		}
+		clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
+	}
 
-		/* Detach the completed transfer before starting queued work. */
-		list_splice_init(&dwc->active_list, &list);
-		list_for_each_entry(desc, &list, desc_node)
-			dma_cookie_complete(&desc->txd);
-		dwc_dostart_first_queued(dwc);
-		spin_unlock_irqrestore(&dwc->lock, flags);
+	if (dma_readl(dw, CH_EN) & dwc->mask) {
+		dev_err(dmaengine_chan_dev(&dwc->chan),
+			"BUG: XFER bit set, but channel not idle!\n");
 
-		list_for_each_entry_safe(desc, _desc, &list, desc_node) {
-			list_del_init(&desc->desc_node);
-			dwc_descriptor_free(dwc, desc, true);
-		}
-		return;
+		/* Try to continue after resetting the channel... */
+		dwc_chan_disable(dw, dwc);
 	}
 
+	dma_cookie_complete(&desc->txd);
+	list_move_tail(&desc->desc_node, &list);
+	dwc_dostart_first_queued(dwc);
+unlock:
 	spin_unlock_irqrestore(&dwc->lock, flags);
+
+	list_for_each_entry_safe(desc, _desc, &list, desc_node) {
+		list_del_init(&desc->desc_node);
+		dwc_descriptor_free(dwc, desc, true);
+	}
 }
 
 static inline void dwc_dump_lli(struct dw_dma_chan *dwc, struct dw_desc *desc)

-- 
2.53.0