ARM: meson: serial: check for tx-irq enabled in irq code

Ensure that if the interrupt handler is entered then only try and do tx
work if the tx irq is enabled.
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Tested-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/meson_uart.c

@@ -237,8 +237,10 @@ static irqreturn_t meson_uart_interrupt(int irq, void *dev_id)
 	if (!(readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY))
 		meson_receive_chars(port);
 
-	if (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_FULL))
+	if (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_FULL)) {
+		if (readl(port->membase + AML_UART_CONTROL) & AML_UART_TX_INT_EN)
 			meson_uart_start_tx(port);
+	}
 
 	spin_unlock(&port->lock);