linux-kernel - [PATCH V2 2/4] dmaengine: xilinx_dma: Fix irq handler and start transfer path for AXI DMA

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Message-ID: <20250710101229.804183-3-suraj.gupta2@amd.com>
Date: Thu, 10 Jul 2025 15:42:27 +0530
From: Suraj Gupta <suraj.gupta2@....com>
To: <andrew+netdev@...n.ch>, <davem@...emloft.net>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <michal.simek@....com>, <vkoul@...nel.org>,
	<radhey.shyam.pandey@....com>
CC: <netdev@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <dmaengine@...r.kernel.org>,
	<harini.katakam@....com>
Subject: [PATCH V2 2/4] dmaengine: xilinx_dma: Fix irq handler and start transfer path for AXI DMA

AXI DMA driver incorrectly assumes complete transfer completion upon
IRQ reception, particularly problematic when IRQ coalescing is active.
Updating the tail pointer dynamically fixes it.
Remove existing idle state validation in the beginning of
xilinx_dma_start_transfer() as it blocks valid transfer initiation on
busy channels with queued descriptors.
Additionally, refactor xilinx_dma_start_transfer() to consolidate coalesce
and delay configurations while conditionally starting channels
only when idle.

Signed-off-by: Suraj Gupta <suraj.gupta2@....com>
Fixes: Fixes: c0bba3a99f07 ("dmaengine: vdma: Add Support for Xilinx AXI Direct Memory Access Engine")
---
 drivers/dma/xilinx/xilinx_dma.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index a34d8f0ceed8..187749b7b8a6 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -1548,9 +1548,6 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 	if (list_empty(&chan->pending_list))
 		return;
 
-	if (!chan->idle)
-		return;
-
 	head_desc = list_first_entry(&chan->pending_list,
 				     struct xilinx_dma_tx_descriptor, node);
 	tail_desc = list_last_entry(&chan->pending_list,
@@ -1558,23 +1555,24 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 	tail_segment = list_last_entry(&tail_desc->segments,
 				       struct xilinx_axidma_tx_segment, node);
 
+	if (chan->has_sg && list_empty(&chan->active_list))
+		xilinx_write(chan, XILINX_DMA_REG_CURDESC,
+			     head_desc->async_tx.phys);
+
 	reg = dma_ctrl_read(chan, XILINX_DMA_REG_DMACR);
 
 	if (chan->desc_pendingcount <= XILINX_DMA_COALESCE_MAX) {
 		reg &= ~XILINX_DMA_CR_COALESCE_MAX;
 		reg |= chan->desc_pendingcount <<
 				  XILINX_DMA_CR_COALESCE_SHIFT;
-		dma_ctrl_write(chan, XILINX_DMA_REG_DMACR, reg);
 	}
 
-	if (chan->has_sg)
-		xilinx_write(chan, XILINX_DMA_REG_CURDESC,
-			     head_desc->async_tx.phys);
 	reg  &= ~XILINX_DMA_CR_DELAY_MAX;
 	reg  |= chan->irq_delay << XILINX_DMA_CR_DELAY_SHIFT;
 	dma_ctrl_write(chan, XILINX_DMA_REG_DMACR, reg);
 
-	xilinx_dma_start(chan);
+	if (chan->idle)
+		xilinx_dma_start(chan);
 
 	if (chan->err)
 		return;
@@ -1914,8 +1912,10 @@ static irqreturn_t xilinx_dma_irq_handler(int irq, void *data)
 		      XILINX_DMA_DMASR_DLY_CNT_IRQ)) {
 		spin_lock(&chan->lock);
 		xilinx_dma_complete_descriptor(chan);
-		chan->idle = true;
-		chan->start_transfer(chan);
+		if (list_empty(&chan->active_list)) {
+			chan->idle = true;
+			chan->start_transfer(chan);
+		}
 		spin_unlock(&chan->lock);
 	}
 
-- 
2.25.1