linux-kernel - [PATCH V2 2/3] dmaengine: xilinx_dma: Enable transfer chaining for AXIDMA and MCDMA by removing idle restriction

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Message-ID: <20251003061910.471575-3-suraj.gupta2@amd.com>
Date: Fri, 3 Oct 2025 11:49:09 +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 V2 2/3] dmaengine: xilinx_dma: Enable transfer chaining for AXIDMA and MCDMA by removing idle restriction

Remove the restrictive idle check in xilinx_dma_start_transfer() and
xilinx_mcdma_start_transfer() that prevented new transfers from being
queued when the channel was busy.
Additionally, only update the CURDESC register when the channel is
running in scatter-gather mode and active list is empty to avoid
interfering with transfers already in progress. When the active list
contains transfers, the hardware tail pointer extension mechanism
handles chaining automatically.

Signed-off-by: Suraj Gupta <suraj.gupta2@....com>
Co-developed-by: Srinivas Neeli <srinivas.neeli@....com>
Signed-off-by: Srinivas Neeli <srinivas.neeli@....com>
---
 drivers/dma/xilinx/xilinx_dma.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 53b82ddad007..aa6589e88c5c 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,
@@ -1567,7 +1564,7 @@ static void xilinx_dma_start_transfer(struct xilinx_dma_chan *chan)
 		dma_ctrl_write(chan, XILINX_DMA_REG_DMACR, reg);
 	}
 
-	if (chan->has_sg)
+	if (chan->has_sg && list_empty(&chan->active_list))
 		xilinx_write(chan, XILINX_DMA_REG_CURDESC,
 			     head_desc->async_tx.phys);
 	reg  &= ~XILINX_DMA_CR_DELAY_MAX;
@@ -1627,9 +1624,6 @@ static void xilinx_mcdma_start_transfer(struct xilinx_dma_chan *chan)
 	if (chan->err)
 		return;
 
-	if (!chan->idle)
-		return;
-
 	if (list_empty(&chan->pending_list))
 		return;
 
@@ -1652,8 +1646,9 @@ static void xilinx_mcdma_start_transfer(struct xilinx_dma_chan *chan)
 	dma_ctrl_write(chan, XILINX_MCDMA_CHAN_CR_OFFSET(chan->tdest), reg);
 
 	/* Program current descriptor */
-	xilinx_write(chan, XILINX_MCDMA_CHAN_CDESC_OFFSET(chan->tdest),
-		     head_desc->async_tx.phys);
+	if (chan->has_sg && list_empty(&chan->active_list))
+		xilinx_write(chan, XILINX_MCDMA_CHAN_CDESC_OFFSET(chan->tdest),
+			     head_desc->async_tx.phys);
 
 	/* Program channel enable register */
 	reg = dma_ctrl_read(chan, XILINX_MCDMA_CHEN_OFFSET);
-- 
2.25.1