dmaengine: xilinx: xilinx_dma: Fix unmasked residue subtraction

[ Upstream commit c7d812e ]

The segment .control and .status fields both contain top bits which are
not part of the buffer size, the buffer size is located only in the bottom
max_buffer_len bits. To avoid interference from those top bits, mask out
the size using max_buffer_len first, and only then subtract the values.

Fixes: a575d0b ("dmaengine: xilinx_dma: Introduce xilinx_dma_get_residue")
Signed-off-by: Marek Vasut <marex@nabladev.com>
Link: https://patch.msgid.link/20260316222530.163815-1-marex@nabladev.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Marek Vasut

drivers/dma/xilinx/xilinx_dma.c

@@ -996,25 +996,25 @@ static u32 xilinx_dma_get_residue(struct xilinx_dma_chan *chan,
 					      struct xilinx_cdma_tx_segment,
 					      node);
 			cdma_hw = &cdma_seg->hw;
-			residue += (cdma_hw->control - cdma_hw->status) &
-				   chan->xdev->max_buffer_len;
+			residue += (cdma_hw->control & chan->xdev->max_buffer_len) -
+			           (cdma_hw->status & chan->xdev->max_buffer_len);
 		} else if (chan->xdev->dma_config->dmatype ==
 			   XDMA_TYPE_AXIDMA) {
 			axidma_seg = list_entry(entry,
 						struct xilinx_axidma_tx_segment,
 						node);
 			axidma_hw = &axidma_seg->hw;
-			residue += (axidma_hw->control - axidma_hw->status) &
-				   chan->xdev->max_buffer_len;
+			residue += (axidma_hw->control & chan->xdev->max_buffer_len) -
+			           (axidma_hw->status & chan->xdev->max_buffer_len);
 		} else {
 			aximcdma_seg =
 				list_entry(entry,
 					   struct xilinx_aximcdma_tx_segment,
 					   node);
 			aximcdma_hw = &aximcdma_seg->hw;
 			residue +=
-				(aximcdma_hw->control - aximcdma_hw->status) &
-				chan->xdev->max_buffer_len;
+				(aximcdma_hw->control & chan->xdev->max_buffer_len) -
+				(aximcdma_hw->status & chan->xdev->max_buffer_len);
 		}
 	}