[09/15] dmaengine: img-mdc: Handle early status read

["Andreas Färber" <afaerber@suse.de>]

From: Damien Horsley <damien.horsley@imgtec.com>

It is possible that mdc_tx_status may be called before the first
node has been read from memory.

In this case, the residue value stored in the register is undefined.
Return the transfer size instead.

Signed-off-by: Damien Horsley <damien.horsley@imgtec.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
---
 drivers/dma/img-mdc-dma.c | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/drivers/dma/img-mdc-dma.c b/drivers/dma/img-mdc-dma.c
index 25cec9c243e1..0f2f0f52d83a 100644
--- a/drivers/dma/img-mdc-dma.c
+++ b/drivers/dma/img-mdc-dma.c
@@ -621,25 +621,33 @@ static enum dma_status mdc_tx_status(struct dma_chan *chan,
 			(MDC_CMDS_PROCESSED_CMDS_DONE_MASK + 1);
 
 		/*
-		 * If the command loaded event hasn't been processed yet, then
-		 * the difference above includes an extra command.
+		 * If the first node has not yet been read from memory,
+		 * the residue register value is undefined
 		 */
-		if (!mdesc->cmd_loaded)
-			cmds--;
-		else
-			cmds += mdesc->list_cmds_done;
-
-		bytes = mdesc->list_xfer_size;
-		ldesc = mdesc->list;
-		for (i = 0; i < cmds; i++) {
-			bytes -= ldesc->xfer_size + 1;
-			ldesc = ldesc->next_desc;
-		}
-		if (ldesc) {
-			if (residue != MDC_TRANSFER_SIZE_MASK)
-				bytes -= ldesc->xfer_size - residue;
+		if (!mdesc->cmd_loaded && !cmds) {
+			bytes = mdesc->list_xfer_size;
+		} else {
+			/*
+			 * If the command loaded event hasn't been processed yet, then
+			 * the difference above includes an extra command.
+			 */
+			if (!mdesc->cmd_loaded)
+				cmds--;
 			else
+				cmds += mdesc->list_cmds_done;
+
+			bytes = mdesc->list_xfer_size;
+			ldesc = mdesc->list;
+			for (i = 0; i < cmds; i++) {
 				bytes -= ldesc->xfer_size + 1;
+				ldesc = ldesc->next_desc;
+			}
+			if (ldesc) {
+				if (residue != MDC_TRANSFER_SIZE_MASK)
+					bytes -= ldesc->xfer_size - residue;
+				else
+					bytes -= ldesc->xfer_size + 1;
+			}
 		}
 	}
 	spin_unlock_irqrestore(&mchan->vc.lock, flags);