serial: 8250_mid: Read RX buffer on RX DMA timeout for DNV

In DNV, when RX DMA is used and number of bytes received is less than
transfer size, only RX DMA timeout interrupt is sent. When this happens,
read the RX buffer.

Signed-off-by: Chuah, Kim Tatt <kim.tatt.chuah@intel.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_mid.c

@@ -96,6 +96,7 @@ static int tng_setup(struct mid8250 *mid, struct uart_port *p)
 static int dnv_handle_irq(struct uart_port *p)
 {
 	struct mid8250 *mid = p->private_data;
+	struct uart_8250_port *up = up_to_u8250p(p);
 	unsigned int fisr = serial_port_in(p, INTEL_MID_UART_DNV_FISR);
 	u32 status;
 	int ret = IRQ_NONE;
@@ -103,9 +104,10 @@ static int dnv_handle_irq(struct uart_port *p)
 
 	if (fisr & BIT(2)) {
 		err = hsu_dma_get_status(&mid->dma_chip, 1, &status);
-		if (err > 0)
+		if (err > 0) {
+			serial8250_rx_dma_flush(up);
 			ret |= IRQ_HANDLED;
-		else if (err == 0)
+		} else if (err == 0)
 			ret |= hsu_dma_do_irq(&mid->dma_chip, 1, status);
 	}
 	if (fisr & BIT(1)) {