HPS uart could not initialize at uboot.

In out case, HPS UART0 is routed to FPGA, HPS UART1 is routed to HPS.

But we found that uboot would hanging while HPS UART0 initializing(before HPS UART0 initialize, HPS UART1 finished initialzing).

The problem is hanging in ns16550.c

while (!(serial_in(&com_port->lsr) & UART_LSR_TEMT))
;

Is there anything we missed if we are making the HPS UART route to FPGA or any change we should make in uboot?