[PATCH v3 14/24] dmaengine: dw-edma: Add LL interrupt placement policy

[Koichiro Den]

Choose LL interrupt positions in the common core. Always request one at
descriptor ends, at the last free slot, and before each link. Add one
every four entries when the rest of the descriptor does not fit or more
issued work follows.

Four entries is an empirically chosen coalescing interval.

Suggested-by: Frank Li <Frank.li@xxxxxxxxxxx>
Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
Changes in v3:
  - Move interrupt placement policy from providers into the common core
    and even use the same four-entry progress interval for eDMA and HDMA.
    (Frank)
  - Move this patch after LL progress reclamation to keep the series
    bisectable.

 drivers/dma/dw-edma/dw-edma-core.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index d4c0be2cbaef..d28e3633a866 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -25,6 +25,9 @@
 #include "../dmaengine.h"
 #include "../virt-dma.h"
 
+/* Empirically chosen progress interval. */
+#define DW_EDMA_LL_PROGRESS_INTERVAL	4
+
 static inline
 struct dw_edma_desc *vd2dw_edma_desc(struct virt_dma_desc *vd)
 {
@@ -250,6 +253,30 @@ static bool dw_edma_ll_done_is_stopped(struct dw_edma_chan *chan)
 	       dw_edma_core_ch_transfer_size(chan) == 0;
 }
 
+static bool dw_edma_core_enable_ll_irq(struct dw_edma_desc *desc, u32 i,
+				       u32 free)
+{
+	struct dw_edma_chan *chan = desc->chan;
+
+	/* Always report descriptor ends and the last free slot. */
+	if (i == desc->nburst - 1 || free == 1)
+		return true;
+
+	/* Keep one progress point per physical ring lap. */
+	if (chan->ll_head == chan->ll_max - 1)
+		return true;
+
+	/*
+	 * Add periodic progress points only while this descriptor does not fit
+	 * in the current free space or more issued work follows it.
+	 */
+	if (desc->nburst - i <= free &&
+	    list_is_last(&desc->vd.node, &chan->vc.desc_issued))
+		return false;
+
+	return (chan->ll_head + 1) % DW_EDMA_LL_PROGRESS_INTERVAL == 0;
+}
+
 static void dw_edma_core_ll_start(struct dw_edma_desc *desc)
 {
 	struct dw_edma_chan *chan = desc->chan;
@@ -271,7 +298,7 @@ static void dw_edma_core_ll_start(struct dw_edma_desc *desc)
 
 		dw_edma_core_ll_data(chan, &desc->burst[i],
 				     chan->ll_head, chan->cb,
-				     i == desc->nburst - 1 || free == 1);
+				     dw_edma_core_enable_ll_irq(desc, i, free));
 
 		chan->ll_head++;
 
-- 
2.51.0