[PATCH] tty: serial: imx: use the sg count from dma_map_sg

[Peng Fan <peng.fan@nxp.com>]

From: Peng Fan <peng.fan@nxp.com>

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".

And update sport->dma_tx_nents with value from dma_map_sg to avoid
modifing dma_unmap_sg

Fixes: b4cdc8f61beb("serial: imx: add DMA support for imx6q")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 drivers/tty/serial/imx.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 87c58f9f6390..bda7f59ec60e 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -619,6 +619,9 @@ static void imx_uart_dma_tx(struct imx_port *sport)
 		dev_err(dev, "DMA mapping error for TX.\n");
 		return;
 	}
+
+	sport->dma_tx_nents = ret;
+
 	desc = dmaengine_prep_slave_sg(chan, sgl, sport->dma_tx_nents,
 					DMA_MEM_TO_DEV, DMA_PREP_INTERRUPT);
 	if (!desc) {
-- 
2.16.4