[PATCH V3 1/4] dmaengine: xilinx_dma: Fix MCDMA descriptor fields based on DMA direction

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

The MCDMA BD format differs between memory-to-device (MM2S) and
device-to-memory (S2MM) directions, but the driver was using generic
'status' and 'sideband_status' fields for both. This led to incorrect
residue calculations when the hardware updates direction-specific fields.

Refactor the descriptor structure to use unions with direction-specific
field mappings, and update the residue calculation logic to select the
correct status field based on DMA direction.

This matches the hardware descriptor layout and fixes incorrect
residue reporting.

Fixes: 6ccd692bfb7f ("dmaengine: xilinx_dma: Add Xilinx AXI MCDMA Engine driver support")
Signed-off-by: Srinivas Neeli <srinivas.neeli@amd.com>
---
Changes in V3:
 - Renamed subject from "for MM2S vs S2MM" to "based on DMA direction".
 - Reworded commit message for clarity.
 - Added XILINX_MCDMA_BD_HW_SIZE macro and static_assert to verify
   descriptor size at compile time.
 - Refactored residue calculation to separate addition and subtraction
   operations for better readability.

Changes in V2:
 - No change.
---
 drivers/dma/xilinx/xilinx_dma.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 98b41b8f8915..ff5b29a808e9 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -223,6 +223,7 @@
 #define XILINX_MCDMA_IRQ_ERR_MASK		BIT(7)
 #define XILINX_MCDMA_BD_EOP			BIT(30)
 #define XILINX_MCDMA_BD_SOP			BIT(31)
+#define XILINX_MCDMA_BD_HW_SIZE			64
 
 /**
  * struct xilinx_vdma_desc_hw - Hardware Descriptor
@@ -277,8 +278,10 @@ struct xilinx_axidma_desc_hw {
  * @buf_addr_msb: MSB of Buffer address @0x0C
  * @rsvd: Reserved field @0x10
  * @control: Control Information field @0x14
- * @status: Status field @0x18
- * @sideband_status: Status of sideband signals @0x1C
+ * @mm2s_ctrl_sideband: Sideband control info for mm2s @0x18
+ * @s2mm_status: Status field for s2mm @0x18
+ * @mm2s_status: Status field for mm2s @0x1C
+ * @s2mm_sideband_status: Sideband status for s2mm @0x1C
  * @app: APP Fields @0x20 - 0x30
  */
 struct xilinx_aximcdma_desc_hw {
@@ -288,10 +291,17 @@ struct xilinx_aximcdma_desc_hw {
 	u32 buf_addr_msb;
 	u32 rsvd;
 	u32 control;
-	u32 status;
-	u32 sideband_status;
+	union {
+		u32 mm2s_ctrl_sideband;
+		u32 s2mm_status;
+	};
+	union {
+		u32 mm2s_status;
+		u32 s2mm_sideband_status;
+	};
 	u32 app[XILINX_DMA_NUM_APP_WORDS];
 } __aligned(64);
+static_assert(sizeof(struct xilinx_aximcdma_desc_hw) == XILINX_MCDMA_BD_HW_SIZE);
 
 /**
  * struct xilinx_cdma_desc_hw - Hardware Descriptor
@@ -1015,9 +1025,11 @@ static u32 xilinx_dma_get_residue(struct xilinx_dma_chan *chan,
 					   struct xilinx_aximcdma_tx_segment,
 					   node);
 			aximcdma_hw = &aximcdma_seg->hw;
-			residue +=
-				(aximcdma_hw->control & chan->xdev->max_buffer_len) -
-				(aximcdma_hw->status & chan->xdev->max_buffer_len);
+			residue += aximcdma_hw->control & chan->xdev->max_buffer_len;
+			if (chan->direction == DMA_DEV_TO_MEM)
+				residue -= aximcdma_hw->s2mm_status & chan->xdev->max_buffer_len;
+			else
+				residue -= aximcdma_hw->mm2s_status & chan->xdev->max_buffer_len;
 		}
 	}
 
-- 
2.25.1