[PATCH AUTOSEL 4.14 352/371] tty: serial: pch_uart: correct usage of dma_unmap_sg

[Sasha Levin <sashal@kernel.org>]

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

[ Upstream commit 74887542fdcc92ad06a48c0cca17cdf09fc8aa00 ]

Per Documentation/DMA-API-HOWTO.txt,
To unmap a scatterlist, just call:
	dma_unmap_sg(dev, sglist, nents, direction);

.. note::

	The 'nents' argument to the dma_unmap_sg call must be
	the _same_ one you passed into the dma_map_sg call,
	it should _NOT_ be the 'count' value _returned_ from the
	dma_map_sg call.

However in the driver, priv->nent is directly assigned with value
returned from dma_map_sg, and dma_unmap_sg use priv->nent for unmap,
this breaks the API usage.

So introduce a new entry orig_nent to remember 'nents'.

Fixes: da3564ee027e ("pch_uart: add multi-scatter processing")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/1573623259-6339-1-git-send-email-peng.fan@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/pch_uart.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index d9123f995705..15ddcbd1f9d2 100644
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -247,6 +247,7 @@ struct eg20t_port {
 	struct dma_chan			*chan_rx;
 	struct scatterlist		*sg_tx_p;
 	int				nent;
+	int				orig_nent;
 	struct scatterlist		sg_rx;
 	int				tx_dma_use;
 	void				*rx_buf_virt;
@@ -801,9 +802,10 @@ static void pch_dma_tx_complete(void *arg)
 	}
 	xmit->tail &= UART_XMIT_SIZE - 1;
 	async_tx_ack(priv->desc_tx);
-	dma_unmap_sg(port->dev, sg, priv->nent, DMA_TO_DEVICE);
+	dma_unmap_sg(port->dev, sg, priv->orig_nent, DMA_TO_DEVICE);
 	priv->tx_dma_use = 0;
 	priv->nent = 0;
+	priv->orig_nent = 0;
 	kfree(priv->sg_tx_p);
 	pch_uart_hal_enable_interrupt(priv, PCH_UART_HAL_TX_INT);
 }
@@ -1027,6 +1029,7 @@ static unsigned int dma_handle_tx(struct eg20t_port *priv)
 		dev_err(priv->port.dev, "%s:dma_map_sg Failed\n", __func__);
 		return 0;
 	}
+	priv->orig_nent = num;
 	priv->nent = nent;
 
 	for (i = 0; i < nent; i++, sg++) {
-- 
2.20.1