[v3,1/5] dmaengine: xilinx_dma: in axidma slave_sg and dma_cylic mode align split descriptors

[Andrea Merello <andrea.merello@gmail.com>]

Whenever a single or cyclic transaction is prepared, the driver
could eventually split it over several SG descriptors in order
to deal with the HW maximum transfer length.

This could end up in DMA operations starting from a misaligned
address. This seems fatal for the HW if DRE is not enabled.

This patch eventually adjusts the transfer size in order to make sure
all operations start from an aligned address.

Cc: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
---
Changes in v2:
        - don't introduce copy_mask field, rather rely on already-esistent
          copy_align field. Suggested by Radhey Shyam Pandey
        - reword title
Changes in v3:
	- fix bug introduced in v2: wrong copy size when DRE is enabled
	  use implementation suggested by Radhey Shyam Pandey
---
 drivers/dma/xilinx/xilinx_dma.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
index 27b523530c4a..113d9bf1b6a1 100644
--- a/drivers/dma/xilinx/xilinx_dma.c
+++ b/drivers/dma/xilinx/xilinx_dma.c
@@ -1793,6 +1793,16 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_slave_sg(
 			 */
 			copy = min_t(size_t, sg_dma_len(sg) - sg_used,
 				     XILINX_DMA_MAX_TRANS_LEN);
+
+			if ((copy + sg_used < sg_dma_len(sg)) &&
+			    chan->xdev->common.copy_align) {
+				/*
+				 * If this is not the last descriptor, make sure
+				 * the next one will be properly aligned
+				 */
+				copy = rounddown(copy,
+					(1 << chan->xdev->common.copy_align));
+			}
 			hw = &segment->hw;
 
 			/* Fill in the descriptor */
@@ -1898,6 +1908,16 @@ static struct dma_async_tx_descriptor *xilinx_dma_prep_dma_cyclic(
 			 */
 			copy = min_t(size_t, period_len - sg_used,
 				     XILINX_DMA_MAX_TRANS_LEN);
+
+			if ((copy + sg_used < period_len) &&
+			    chan->xdev->common.copy_align) {
+				/*
+				 * If this is not the last descriptor, make sure
+				 * the next one will be properly aligned
+				 */
+				copy = rounddown(copy,
+					(1 << chan->xdev->common.copy_align));
+			}
 			hw = &segment->hw;
 			xilinx_axidma_buf(chan, hw, buf_addr, sg_used,
 					  period_len * i);