linux-kernel - [PATCH 3/3] dmaengine: xilinx_dma: Optimize control register write and channel start logic in xilinx_dma_start

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Message-ID: <20250917133609.231316-4-suraj.gupta2@amd.com>
Date: Wed, 17 Sep 2025 19:06:09 +0530
From: Suraj Gupta <suraj.gupta2@....com>
To: <vkoul@...nel.org>, <radhey.shyam.pandey@....com>, <michal.simek@....com>
CC: <dmaengine@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH 3/3] dmaengine: xilinx_dma: Optimize control register write and channel start logic in xilinx_dma_start_transfer

Optimize AXI DMA control register programming by consolidating
coalesce count and delay configuration into a single register write.
Previously, the coalesce count was written separately from the delay
configuration, resulting in two register writes. Combine these into
one write operation to reduce bus overhead.
Additionally, avoid redundant channel starts by only calling
xilinx_dma_start() when the channel is actually idle.

Signed-off-by: Suraj Gupta <suraj.gupta2@....com>
---
 drivers/dma/xilinx/xilinx_dma.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 7211c394cdca..6e9bf4732ded 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -1561,7 +1561,6 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 		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 && list_empty(&chan->active_list))
@@ -1571,7 +1570,8 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 	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;
-- 
2.25.1