serial: altera: don't enable any irq if the device doesn't feature an irq

If the irq line of an altera UART device isn't used to report interrupts
for this device the driver better ensures that this device doesn't pull
this line to active state and so disturb the whatever might be connected
to this line.

Signed-off-by: Uwe Kleine-König <[e-mail]>
Acked-by: Tobias Klauser <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/altera_uart.c

···
 	return sigs;
 }
 
+static void altera_uart_update_ctrl_reg(struct altera_uart *pp)
+{
+	unsigned short imr = pp->imr;
+
+	/*
+	 * If the device doesn't have an irq, ensure that the irq bits are
+	 * masked out to keep the irq line inactive.
+	 */
+	if (!pp->port.irq)
+		imr &= ALTERA_UART_CONTROL_TRBK_MSK | ALTERA_UART_CONTROL_RTS_MSK;
+
+	altera_uart_writel(&pp->port, imr, ALTERA_UART_CONTROL_REG);
+}
+
 static void altera_uart_set_mctrl(struct uart_port *port, unsigned int sigs)
 {
 	struct altera_uart *pp = container_of(port, struct altera_uart, port);
···
 		pp->imr |= ALTERA_UART_CONTROL_RTS_MSK;
 	else
 		pp->imr &= ~ALTERA_UART_CONTROL_RTS_MSK;
-	altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+	altera_uart_update_ctrl_reg(pp);
 }
 
 static void altera_uart_start_tx(struct uart_port *port)
···
 	struct altera_uart *pp = container_of(port, struct altera_uart, port);
 
 	pp->imr |= ALTERA_UART_CONTROL_TRDY_MSK;
-	altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+	altera_uart_update_ctrl_reg(pp);
 }
 
 static void altera_uart_stop_tx(struct uart_port *port)
···
 	struct altera_uart *pp = container_of(port, struct altera_uart, port);
 
 	pp->imr &= ~ALTERA_UART_CONTROL_TRDY_MSK;
-	altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+	altera_uart_update_ctrl_reg(pp);
 }
 
 static void altera_uart_stop_rx(struct uart_port *port)
···
 	struct altera_uart *pp = container_of(port, struct altera_uart, port);
 
 	pp->imr &= ~ALTERA_UART_CONTROL_RRDY_MSK;
-	altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+	altera_uart_update_ctrl_reg(pp);
 }
 
 static void altera_uart_break_ctl(struct uart_port *port, int break_state)
···
 		pp->imr |= ALTERA_UART_CONTROL_TRBK_MSK;
 	else
 		pp->imr &= ~ALTERA_UART_CONTROL_TRBK_MSK;
-	altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+	altera_uart_update_ctrl_reg(pp);
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
···
 
 	if (xmit->head == xmit->tail) {
 		pp->imr &= ~ALTERA_UART_CONTROL_TRDY_MSK;
-		altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+		altera_uart_update_ctrl_reg(pp);
 	}
 }
 
···
 
 	/* Enable RX interrupts now */
 	pp->imr = ALTERA_UART_CONTROL_RRDY_MSK;
-	altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+	altera_uart_update_ctrl_reg(pp);
 
 	spin_unlock_irqrestore(&port->lock, flags);
 
···
 
 	/* Disable all interrupts now */
 	pp->imr = 0;
-	altera_uart_writel(port, pp->imr, ALTERA_UART_CONTROL_REG);
+	altera_uart_update_ctrl_reg(pp);
 
 	spin_unlock_irqrestore(&port->lock, flags);