kern/51349: kernel fails to boot on radeon if firmware file is missing

[gdt%ir.bbn.com@localhost]

>Number:         51349
>Category:       kern
>Synopsis:       kernel fails to boot on radeon if firmware file is missing
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jul 20 17:45:00 +0000 2016
>Originator:     Greg Troxel
>Release:        NetBSD 7.0_STABLE
>Organization:
    BBN
>Environment:
amd64
Dell Optiplex 990
>Description:
When booting a netbsd-7 kernel with netbsd-6 userland, the kernel
fails to load the radeon microcode, and then panics because there is
no working console.

See

https://mail-index.netbsd.org/netbsd-users/2016/07/18/msg018687.html

for dmesg snippets.

This can be worked around by adding "userconf disable radeon*;" in a
boot.cfg line.

>How-To-Repeat:
Install netbsd-6.  Change to a netbsd-7 kernel, but don't update
userland.

>Fix:
Make firmware loading either succeed, or fail by rolling back to the
pre-load state, so that the console is still usable.  Actually, the
panic messages are printed fine, so it seems the problem is believing
the console is not usable, not it actually being broken.

>Unformatted:
 sources as of about 7/18