[PATCH V3 2/4] dmaengine: xilinx_dma: Move descriptors to done list based on completion bit

[Srinivas Neeli <srinivas.neeli@amd.com>]

In AXI MCDMA scatter-gather mode, xilinx_dma_complete_descriptor() walks
the channel's active_list and unconditionally moves every entry to the
done_list. The MCDMA IOC interrupt handler invokes this function on
every interrupt-on-completion, but with interrupt coalescing
(IRQThreshold > 1) an IOC interrupt may fire after only a subset of the
queued descriptors have actually been processed by the hardware. As a
result, descriptors whose completion bit is not yet set in the BD status
were being reported as completed to client drivers.

Add a check for the descriptor completion bit before moving entries from
the active list to the done list, using the appropriate direction-
specific status field (s2mm_status for DMA_DEV_TO_MEM, mm2s_status for
DMA_MEM_TO_DEV).

The MCDMA completion check is intentionally not guarded by chan->has_sg,
unlike the AXIDMA branch above. AXI MCDMA only operates in scatter-gather
mode (has_sg is always true), so the guard would always pass and is
omitted. The completion bit is therefore checked unconditionally.

Fixes: 6ccd692bfb7f ("dmaengine: xilinx_dma: Add Xilinx AXI MCDMA Engine driver support")
Signed-off-by: Srinivas Neeli <srinivas.neeli@amd.com>
---
Changes in V3:
 - Added Fixes tag.
 - Expanded commit message to explain the interrupt coalescing scenario
   and why the has_sg guard is omitted for MCDMA.
 - Changed local variable from 'bool completed' to 'u32 status' for
   cleaner status field access.
 - Simplified completion check logic.

Changes in V2:
 - No change.
---
 drivers/dma/xilinx/xilinx_dma.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index ff5b29a808e9..1b5b00f08c5f 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -1784,6 +1784,17 @@ static void xilinx_dma_complete_descriptor(struct xilinx_dma_chan *chan)
 					      struct xilinx_axidma_tx_segment, node);
 			if (!(seg->hw.status & XILINX_DMA_BD_COMP_MASK) && chan->has_sg)
 				break;
+		} else if (chan->xdev->dma_config->dmatype == XDMA_TYPE_AXIMCDMA) {
+			struct xilinx_aximcdma_tx_segment *seg;
+			u32 status;
+
+			seg = list_last_entry(&desc->segments,
+					      struct xilinx_aximcdma_tx_segment,
+					      node);
+			status = (chan->direction == DMA_DEV_TO_MEM) ?
+				seg->hw.s2mm_status : seg->hw.mm2s_status;
+			if (!(status & XILINX_DMA_BD_COMP_MASK))
+				break;
 		}
 		if (chan->has_sg && chan->xdev->dma_config->dmatype !=
 		    XDMA_TYPE_VDMA)
-- 
2.25.1