[PATCH v2 08/19] dmaengine: dw-edma: Centralize LL doorbell decisions

[Koichiro Den]

LL fill currently rings the doorbell every time. A running eDMA or HDMA
channel follows entries whose CB matches CCS without another kick. A
channel stopped at a CB mismatch needs one.

Move that decision to dw_edma_core_ch_maybe_doorbell(). It rings only for
a BUSY LL channel with pending entries, no EDMA_REQ_STOP or
EDMA_REQ_PAUSE, and hardware that is not running. The BUSY check prevents
EDMA_REQ_STOP completion from restarting terminated work.

issue_pending() still publishes LL entries only from IDLE. A later patch
allows live appends. Non-LL channels are unchanged.

Signed-off-by: Koichiro Den <den@xxxxxxxxxxxxx>
---
Changes in v2:
  - New patch.

 drivers/dma/dw-edma/dw-edma-core.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index fa104af4146e..e88bfb417ad4 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -129,6 +129,11 @@ static bool dw_edma_core_enable_ll_irq(struct dw_edma_desc *desc, u32 i,
 	return desc->chan->dw->core->ll_irq(desc, i, free);
 }
 
+static bool dw_edma_ll_pending(struct dw_edma_chan *chan)
+{
+	return chan->ll_head != chan->ll_end;
+}
+
 static void dw_edma_core_ll_start(struct dw_edma_desc *desc)
 {
 	struct dw_edma_chan *chan = desc->chan;
@@ -163,8 +168,6 @@ static void dw_edma_core_ll_start(struct dw_edma_desc *desc)
 
 	desc->done_burst = desc->start_burst;
 	desc->start_burst = i;
-
-	dw_edma_core_ch_doorbell(chan);
 }
 
 static void dw_edma_core_start(struct dw_edma_desc *desc)
@@ -232,6 +235,23 @@ static void dw_edma_terminate_all_descs(struct dw_edma_chan *chan)
 	dw_edma_terminate_vdesc_list(&chan->vc.desc_submitted);
 }
 
+/* Must be called with vc.lock held. */
+static void dw_edma_core_ch_maybe_doorbell(struct dw_edma_chan *chan)
+{
+	if (chan->non_ll || chan->request != EDMA_REQ_NONE ||
+	    chan->status != EDMA_ST_BUSY || !dw_edma_ll_pending(chan))
+		return;
+
+	/*
+	 * While running, both legacy eDMA and HDMA consume newly published
+	 * elements without another doorbell.
+	 */
+	if (dw_edma_core_ch_status(chan) == DMA_IN_PROGRESS)
+		return;
+
+	dw_edma_core_ch_doorbell(chan);
+}
+
 static void dw_edma_device_caps(struct dma_chan *dchan,
 				struct dma_slave_caps *caps)
 {
@@ -357,6 +377,7 @@ static int dw_edma_device_resume(struct dma_chan *dchan)
 		chan->status = EDMA_ST_BUSY;
 		if (!dw_edma_start_transfer(chan))
 			chan->status = EDMA_ST_IDLE;
+		dw_edma_core_ch_maybe_doorbell(chan);
 	}
 
 	return err;
@@ -405,6 +426,7 @@ static void dw_edma_device_issue_pending(struct dma_chan *dchan)
 	    chan->status == EDMA_ST_IDLE) {
 		chan->status = EDMA_ST_BUSY;
 		dw_edma_start_transfer(chan);
+		dw_edma_core_ch_maybe_doorbell(chan);
 	}
 	spin_unlock_irqrestore(&chan->vc.lock, flags);
 }
@@ -720,6 +742,8 @@ static void dw_edma_done_interrupt(struct dw_edma_chan *chan)
 	default:
 		break;
 	}
+	dw_edma_core_ch_maybe_doorbell(chan);
+
 	spin_unlock_irqrestore(&chan->vc.lock, flags);
 }
 
-- 
2.51.0