ATMEL_US_IMR
mask = atmel_uart_readl(port, ATMEL_US_IMR);
atmel_port->backup_imr = atmel_uart_readl(port, ATMEL_US_IMR);
imr = atmel_uart_readl(port, ATMEL_US_IMR);
imr = atmel_uart_readl(port, ATMEL_US_IMR);
atmel_port->cache.imr = atmel_uart_readl(port, ATMEL_US_IMR);