serial: omap: simplify IRQ handling

quite a few changes here, though they are
pretty obvious. In summary we're making sure
to detect which interrupt type we need to
handle before calling the underlying interrupt
handling procedure.
Tested-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/omap-serial.c

@@ -351,33 +351,58 @@ static inline irqreturn_t serial_omap_irq(int irq, void *dev_id)
 {
 	struct uart_omap_port *up = dev_id;
 	unsigned int iir, lsr;
+	unsigned int type;
 	unsigned long flags;
+	irqreturn_t ret = IRQ_NONE;
 
+	spin_lock_irqsave(&up->port.lock, flags);
 	pm_runtime_get_sync(up->dev);
 	iir = serial_in(up, UART_IIR);
-	if (iir & UART_IIR_NO_INT) {
-		pm_runtime_mark_last_busy(up->dev);
-		pm_runtime_put_autosuspend(up->dev);
-		return IRQ_NONE;
-	}
+again:
+	if (iir & UART_IIR_NO_INT)
+		goto out;
 
-	spin_lock_irqsave(&up->port.lock, flags);
+	ret = IRQ_HANDLED;
 	lsr = serial_in(up, UART_LSR);
-	if (iir & UART_IIR_RLSI) {
-		if (lsr & UART_LSR_DR)
-			receive_chars(up, &lsr);
-	}
 
+	/* extract IRQ type from IIR register */
+	type = iir & 0x3e;
+
+	switch (type) {
+	case UART_IIR_MSI:
 		check_modem_status(up);
-	if ((lsr & UART_LSR_THRE) && (iir & UART_IIR_THRI))
+		break;
+	case UART_IIR_THRI:
+		if (lsr & UART_LSR_THRE)
 			transmit_chars(up);
+		break;
+	case UART_IIR_RDI:
+		if (lsr & UART_LSR_DR)
+			receive_chars(up, &lsr);
+		break;
+	case UART_IIR_RLSI:
+		if (lsr & UART_LSR_BRK_ERROR_BITS)
+			receive_chars(up, &lsr);
+		break;
+	case UART_IIR_RX_TIMEOUT:
+		receive_chars(up, &lsr);
+		break;
+	case UART_IIR_CTS_RTS_DSR:
+		iir = serial_in(up, UART_IIR);
+		goto again;
+	case UART_IIR_XOFF:
+		/* FALLTHROUGH */
+	default:
+		break;
+	}
 
+out:
 	spin_unlock_irqrestore(&up->port.lock, flags);
 	pm_runtime_mark_last_busy(up->dev);
 	pm_runtime_put_autosuspend(up->dev);
-
 	up->port_activity = jiffies;
-	return IRQ_HANDLED;
+
+	return ret;
 }
 
 static unsigned int serial_omap_tx_empty(struct uart_port *port)