[PATCH v5 05/10] dmaengine: dw: calculate residue in the status getter

[James Hilliard <james.hilliard1@gmail.com>]

From: Serge Semin <fancer.lancer@gmail.com>

Calculate hardware-LLP residue while looking up the requested cookie under
the channel lock. The scanner and the status getter currently take that
lock separately, allowing a descriptor to start between the scanner's
residue update and the status query.

Have dwc_get_hard_llp_desc_residue() return a local residue value from a
fresh LLP snapshot. Keep the persistent residue field for software-LLP
block accounting, subtracting the current block's progress when reporting
status. The descriptor scanner continues to advance software-LLP blocks
and complete cookies from RAW.XFER, including for polled transfers.

Fixes: 3bfb1d20b547 ("dmaengine: Driver for the Synopsys DesignWare DMA controller")
Cc: stable@vger.kernel.org
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
[james: retain polled completion and software-LLP progress]
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>

---

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 | 88 ++++++++++++++++++---------------------------------
 1 file changed, 31 insertions(+), 57 deletions(-)

diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 5a1caca7ad68..0d6b5bd8ea6b 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -267,41 +267,8 @@ static inline u32 dwc_get_sent(struct dw_dma_chan *dwc)
 	return dw->block2bytes(dwc, ctlhi, ctllo >> 4 & 7);
 }
 
-static bool dwc_get_hard_llp_desc_residue(struct dw_dma_chan *dwc,
-				       struct dw_desc *desc, dma_addr_t llp)
-{
-	struct dw_desc *child;
-
-	/* Initial residue value */
-	desc->residue = desc->total_len;
-
-	/* Check first descriptors addr */
-	if (desc->txd.phys == DWC_LLP_LOC(llp))
-		return true;
-
-	/* Check first descriptors llp */
-	if (lli_read(desc, llp) == llp) {
-		/* This one is currently in progress */
-		desc->residue -= dwc_get_sent(dwc);
-		return true;
-	}
-
-	desc->residue -= desc->len;
-	list_for_each_entry(child, &desc->tx_list, desc_node) {
-		if (lli_read(child, llp) == llp) {
-			/* Currently in progress */
-			desc->residue -= dwc_get_sent(dwc);
-			return true;
-		}
-		desc->residue -= child->len;
-	}
-
-	return false;
-}
-
 static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
 {
-	dma_addr_t llp;
 	struct dw_desc *desc, *_desc;
 	struct dw_desc *child;
 	u32 status_xfer;
@@ -309,7 +276,6 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
 	LIST_HEAD(list);
 
 	spin_lock_irqsave(&dwc->lock, flags);
-	llp = channel_readl(dwc, LLP);
 	status_xfer = dma_readl(dw, RAW.XFER);
 
 	if (status_xfer & dwc->mask) {
@@ -372,27 +338,6 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
 		return;
 	}
 
-	if (list_empty(&dwc->active_list)) {
-		spin_unlock_irqrestore(&dwc->lock, flags);
-		return;
-	}
-
-	if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
-		dev_vdbg(dmaengine_chan_dev(&dwc->chan), "%s: soft LLP mode\n", __func__);
-		spin_unlock_irqrestore(&dwc->lock, flags);
-		return;
-	}
-
-	dev_vdbg(dmaengine_chan_dev(&dwc->chan), "%s: llp=%pad\n", __func__, &llp);
-
-	list_for_each_entry_safe(desc, _desc, &dwc->active_list, desc_node) {
-		if (dwc_get_hard_llp_desc_residue(dwc, desc, llp)) {
-			spin_unlock_irqrestore(&dwc->lock, flags);
-			return;
-		}
-	}
-
-	/* Residue describes source reads; only RAW.XFER completes a transfer. */
 	spin_unlock_irqrestore(&dwc->lock, flags);
 }
 
@@ -975,6 +920,32 @@ static struct dw_desc *dwc_find_desc(struct dw_dma_chan *dwc, dma_cookie_t c)
 	return NULL;
 }
 
+static u32 dwc_get_hard_llp_desc_residue(struct dw_dma_chan *dwc, struct dw_desc *desc)
+{
+	u32 residue = desc->total_len;
+	struct dw_desc *child;
+	dma_addr_t llp;
+
+	llp = channel_readl(dwc, LLP);
+
+	/* The first descriptor may still be waiting to be fetched. */
+	if (desc->txd.phys == DWC_LLP_LOC(llp))
+		return residue;
+
+	if (lli_read(desc, llp) == llp)
+		return residue - dwc_get_sent(dwc);
+
+	residue -= desc->len;
+	list_for_each_entry(child, &desc->tx_list, desc_node) {
+		if (lli_read(child, llp) == llp)
+			return residue - dwc_get_sent(dwc);
+
+		residue -= child->len;
+	}
+
+	return residue;
+}
+
 static u32 dwc_get_residue_and_status(struct dw_dma_chan *dwc, dma_cookie_t cookie,
 				      enum dma_status *status)
 {
@@ -987,9 +958,12 @@ static u32 dwc_get_residue_and_status(struct dw_dma_chan *dwc, dma_cookie_t cook
 	desc = dwc_find_desc(dwc, cookie);
 	if (desc) {
 		if (desc == dwc_first_active(dwc)) {
-			residue = desc->residue;
-			if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags) && residue)
+			if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
+				residue = desc->residue;
 				residue -= dwc_get_sent(dwc);
+			} else {
+				residue = dwc_get_hard_llp_desc_residue(dwc, desc);
+			}
 			if (test_bit(DW_DMA_IS_PAUSED, &dwc->flags))
 				*status = DMA_PAUSED;
 		} else {

-- 
2.53.0