[PATCH V2 1/3] dmaengine: xilinx_dma: Fix channel idle state management in AXIDMA and MCDMA interrupt handlers

[Suraj Gupta]

Fix a race condition in AXIDMA and MCDMA irq handlers where the channel
could be incorrectly marked as idle and attempt spurious transfers when
descriptors are still being processed.

The issue occurs when:
1. Multiple descriptors are queued and active.
2. An interrupt fires after completing some descriptors.
3. xilinx_dma_complete_descriptor() moves completed descriptors to
done_list.
4. Channel is marked idle and start_transfer() is called even though
   active_list still contains unprocessed descriptors.
5. This leads to premature transfer attempts and potential descriptor
   corruption or missed completions.

Only mark the channel as idle and start new transfers when the active list
is actually empty, ensuring proper channel state management and avoiding
spurious transfer attempts.

Signed-off-by: Suraj Gupta <suraj.gupta2 at amd.com>
Co-developed-by: Srinivas Neeli <srinivas.neeli at amd.com>
Signed-off-by: Srinivas Neeli <srinivas.neeli at amd.com>
Fixes: c0bba3a99f07 ("dmaengine: vdma: Add Support for Xilinx AXI Direct Memory Access Engine")
---
 drivers/dma/xilinx/xilinx_dma.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index fabff602065f..53b82ddad007 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -1857,8 +1857,10 @@ static irqreturn_t xilinx_mcdma_irq_handler(int irq, void *data)
 	if (status & XILINX_MCDMA_IRQ_IOC_MASK) {
 		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);
 	}
 
@@ -1914,8 +1916,10 @@ 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