port-amd64/53738: the bootloader does not accept console inputs in PCEngines APU2

[clare%csel.org@localhost]

>Number:         53738
>Category:       port-amd64
>Synopsis:       the bootloader does not accept console inputs in PCEngines APU2
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Nov 24 16:25:00 +0000 2018
>Originator:     Shinichi Doyashiki
>Release:        NetBSD 8.0_STABLE
>Organization:
	at home
>Environment:
System: NetBSD devel.csel.org 8.0_STABLE NetBSD 8.0_STABLE (APU1C_8) #4: Sun Nov 11 19:47:16 JST 2018 clare%devel.csel.org@localhost:/export/stage/stable-8/src/sys/arch/amd64/compile/APU1C_8 amd64
Architecture: x86_64
Machine: amd64
>Description:
        The PCEngines APUx system is only works in serial console.
	The its BIOS handles console input/output via serial port
	by the default, but the bootloader configured in serial
	console mode does not accept inputs from serial console.
	The bootloader should take inputs from serial port in serial
	console mode.

>How-To-Repeat:
	1. get APU2D4 system board from PCEngines.
	2. get most recent mainline BIOS (firmware) from github
	   and install to the box.  https://pcengines.github.io/
	3. installboot -v -o console=com,speed=115200 [device] [bootxx]
	4. reboot.
	5. you will see the bootloader does not accept any inputs.

>Fix:
	Unknown yet.

	To a workaround, you can use the kernel option CONS_OVERRIDE
	to enforce kernel using serial console, and leave the bootloader
	to use the BIOS (PC console) to input/output.  the recent
	APU2D4's BIOS can provide input/output from serial console
	for the bootloader.