CDNS_UART_ISR
writel(readl(port->membase + CDNS_UART_ISR),
port->membase + CDNS_UART_ISR);
writel(0xffffffff, port->membase + CDNS_UART_ISR);
isrstatus = readl(port->membase + CDNS_UART_ISR);
writel(isrstatus, port->membase + CDNS_UART_ISR);
writel(CDNS_UART_IXR_TXEMPTY, port->membase + CDNS_UART_ISR);