tty: serial: pch_uart: correct usage of dma_unmap_sg

commit 74887542fdcc92ad06a48c0cca17cdf09fc8aa00 upstream.

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>

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index 6157213..c16234b 100644 (file)
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -233,6 +233,7 @@ 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;
@@ -787,9 +788,10 @@ 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);
 }
@@ -1010,6 +1012,7 @@ 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++) {