serial: fsl_lpuart: move DMA RX timeout calculation

The DMA RX timeout calculation is done based on FIFO buffer size and
port timeout when setting up DMA. However, both variables are not
necessarily initialized at DMA initialization time, which can lead
to a division by zero.

Move the timeout calculation to set_termios where both variables
are initialized.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/fsl_lpuart.c

@@ -720,13 +720,6 @@ static int lpuart_dma_rx_request(struct uart_port *port)
 	sport->dma_rx_buf_bus = dma_bus;
 	sport->dma_rx_in_progress = 0;
 
-	sport->dma_rx_timeout = (sport->port.timeout - HZ / 50) *
-				FSL_UART_RX_DMA_BUFFER_SIZE * 3 /
-				sport->rxfifo_size / 2;
-
-	if (sport->dma_rx_timeout < msecs_to_jiffies(20))
-		sport->dma_rx_timeout = msecs_to_jiffies(20);
-
 	return 0;
 }
 
@@ -918,6 +911,17 @@ lpuart_set_termios(struct uart_port *port, struct ktermios *termios,
 	/* update the per-port timeout */
 	uart_update_timeout(port, termios->c_cflag, baud);
 
+	if (sport->lpuart_dma_use) {
+		/* Calculate delay for 1.5 DMA buffers */
+		sport->dma_rx_timeout = (sport->port.timeout - HZ / 50) *
+					FSL_UART_RX_DMA_BUFFER_SIZE * 3 /
+					sport->rxfifo_size / 2;
+		dev_dbg(port->dev, "DMA Rx t-out %ums, tty t-out %u jiffies\n",
+			sport->dma_rx_timeout * 1000 / HZ, sport->port.timeout);
+		if (sport->dma_rx_timeout < msecs_to_jiffies(20))
+			sport->dma_rx_timeout = msecs_to_jiffies(20);
+	}
+
 	/* wait transmit engin complete */
 	while (!(readb(sport->port.membase + UARTSR1) & UARTSR1_TC))
 		barrier();