64-bit pi 3 grief

[Andrew Cagney <andrew.cagney%gmail.com@localhost>]

For the moment some notes.  Once I've switched from hdmi to serial
(I'm trying to avoid posting screen shots), I'll hopefully be able to
capture more details.

setup #1:
- Pi3 with latest 9 GENERIC64 kernel on SD card; cross compiled from linux
- root=sd0a console=fb
- wired ethernet
- usb keyboard
- sd0a is a usb/ssd (configured using kernel command line param)
It boots fine but building NetBSD would generate USB disk errors and
locks up.  Being suspicious of the SSD (it's old, its cheap) I decide
to switch.
Still, have to ask, has anyone cross compiled 64-bit netbsd arm, using
64-bit netbsd arm with 1GB of ram?

setup #2:
- Pi3 with latest 9 GENERIC64 kernel on SD card; cross compiled from linux
- root=sd0a console=fb
- wired ethernet
but:
- *no usb keyboard*
- sd0a is a usb/*spinning-disk* (configured kernel boot param)
Now I hit two problems:
#1: the kernel doesn't wait for the sd0 to come online and instead
prompts for the root device (I hit this long ago on an odroid, and the
SSD was a workaround ...)
#2: the prompt displays "root device: ld0", I think it should have
displayed "root device: sd0a" since that is what was specified
Should "init" have waited longer for "sd0a" before prompting for the
root device (perhaps it waited for ld0?).  Since "sd0" does come
online while "init" is sitting at the "root device" prompt, should
"init" be able to detect this?
Any workarounds?  I"m building a custom kernel with "root on sd0" to
see if it helps.

setup #3:
- Pi3 with latest 9 GENERIC64 kernel on SD card; cross compiled from linux
- root=sd0a console=fb
- wired ethernet
but:
- usb keyboard (either from power-up, or plugged in after the "root
device" prompt)
- sd0a is a usb/*spinning-disk* (configured kernel boot param)
Kaboom.  Based on the HIDs and USBs in the backtrace, and page upon
page of what look like usb message dumps, I'm guessing its the kernel
trying to read the keyboard.