[PATCH 4.19 006/243] tty: serial: fsl_lpuart: use the sg count from dma_map_sg

[Greg Kroah-Hartman]

From: Peng Fan <peng.fan@xxxxxxx>

commit 487ee861de176090b055eba5b252b56a3b9973d6 upstream.

The dmaengine_prep_slave_sg needs to use sg count returned
by dma_map_sg, not use sport->dma_tx_nents, because the return
value of dma_map_sg is not always same with "nents".

When enabling iommu for lpuart + edma, iommu framework may concatenate
two sgs into one.

Fixes: 6250cc30c4c4e ("tty: serial: fsl_lpuart: Use scatter/gather DMA for Tx")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
Link: https://lore.kernel.org/r/1572932977-17866-1-git-send-email-peng.fan@xxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/fsl_lpuart.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -376,8 +376,8 @@ static void lpuart_dma_tx(struct lpuart_
 	}
 
 	sport->dma_tx_desc = dmaengine_prep_slave_sg(sport->dma_tx_chan, sgl,
-					sport->dma_tx_nents,
-					DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT);
+					ret, DMA_MEM_TO_DEV,
+					DMA_PREP_INTERRUPT);
 	if (!sport->dma_tx_desc) {
 		dma_unmap_sg(dev, sgl, sport->dma_tx_nents, DMA_TO_DEVICE);
 		dev_err(dev, "Cannot prepare TX slave DMA!\n");