serial: 8250: Extract IIR logic steering from rx dma

Using fake IIR values to perform rx dma operations unnecessarily
conflates separate operations, stopping in-progress dma with starting
new dma.

Introduce serial8250_rx_dma_flush() to handle stopping in-progress dma
[omap8250 already has equivalent omap_8250_rx_dma_flush()].
Replace rx_dma(UART_IIR_RX_TIMEOUT) with the equivalent *_rx_dma_flush(),
and rx_dma(0) with the equivalent *_rx_dma(). Handle IIR steering
in the irq handler with handle_rx_dma() helper.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250.h

@@ -17,7 +17,7 @@
 
 struct uart_8250_dma {
 	int (*tx_dma)(struct uart_8250_port *p);
-	int (*rx_dma)(struct uart_8250_port *p, unsigned int iir);
+	int (*rx_dma)(struct uart_8250_port *p);
 
 	/* Filter function */
 	dma_filter_fn		fn;
@@ -189,7 +189,8 @@ static inline int is_omap1510_8250(struct uart_8250_port *pt)
 
 #ifdef CONFIG_SERIAL_8250_DMA
 extern int serial8250_tx_dma(struct uart_8250_port *);
-extern int serial8250_rx_dma(struct uart_8250_port *, unsigned int iir);
+extern int serial8250_rx_dma(struct uart_8250_port *);
+extern void serial8250_rx_dma_flush(struct uart_8250_port *);
 extern int serial8250_request_dma(struct uart_8250_port *);
 extern void serial8250_release_dma(struct uart_8250_port *);
 #else
@@ -197,10 +198,11 @@ static inline int serial8250_tx_dma(struct uart_8250_port *p)
 {
 	return -1;
 }
-static inline int serial8250_rx_dma(struct uart_8250_port *p, unsigned int iir)
+static inline int serial8250_rx_dma(struct uart_8250_port *p)
 {
 	return -1;
 }
+static inline void serial8250_rx_dma_flush(struct uart_8250_port *p) { }
 static inline int serial8250_request_dma(struct uart_8250_port *p)
 {
 	return -1;