[PATCH V2 7/8] dmaengine: zynqmp_dma: Reject zero-length memcpy transfers

[Golla Nagendra <nagendra.golla@amd.com>]

Zero-length prep_memcpy() needlessly consumed a descriptor slot. Reject
zero-length memcpy at prep time and document the behaviour.

Signed-off-by: Golla Nagendra <nagendra.golla@amd.com>
---
Changes in V2:
- No change
---
 drivers/dma/xilinx/zynqmp_dma.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/dma/xilinx/zynqmp_dma.c b/drivers/dma/xilinx/zynqmp_dma.c
index 194abfd6cb25..921d3d9f6ed6 100644
--- a/drivers/dma/xilinx/zynqmp_dma.c
+++ b/drivers/dma/xilinx/zynqmp_dma.c
@@ -837,7 +837,8 @@ static void zynqmp_dma_synchronize(struct dma_chan *dchan)
  * @len: Transfer length
  * @flags: transfer ack flags
  *
- * Return: Async transaction descriptor on success and NULL on failure
+ * Return: Async transaction descriptor on success and NULL on failure or
+ *	   zero length transfer
  */
 static struct dma_async_tx_descriptor *zynqmp_dma_prep_memcpy(
 				struct dma_chan *dchan, dma_addr_t dma_dst,
@@ -852,6 +853,9 @@ static struct dma_async_tx_descriptor *zynqmp_dma_prep_memcpy(
 
 	chan = to_chan(dchan);
 
+	if (!len)
+		return NULL;
+
 	desc_cnt = DIV_ROUND_UP(len, ZYNQMP_DMA_MAX_TRANS_LEN);
 
 	spin_lock_irqsave(&chan->lock, irqflags);
-- 
2.44.4