Thanks for your replies.
Yes I'm observing both serial and VGA outputs.
Ronald Maas shared this earlycon magic:
earlycon=uart8250,mmio32,0x1c020000
and now I can see how the Debian installer kernel fails:
EFI stub: Booting Linux Kernel...
ConvertPages: Incompatible memory types
EFI stub: EFI_RNG_PROTOCOL unavailable, no randomness supplied
EFI stub: Using DTB from configuration table
EFI stub: Exiting boot services and installing virtual address map...
OSBootEvent = Success
L3c Cache: 8MB
[ 0.000000] Booting Linux on physical CPU 0x0
[ 0.000000] Linux version 4.6.0-1-arm64
(debian-ker...@lists.debian.org) (gcc version 5.4.0 20160609 (Debian
5.4.0-4) ) #1 SMP Debian 4.6.2-2 (2016-06-25)
[ 0.000000] Boot CPU: AArch64 Processor [500f0001]
[ 0.000000] earlycon: uart8250 at MMIO32 0x000000001c020000 (options '')
[ 0.000000] bootconsole [uart8250] enabled
[ 0.000000] efi: Getting EFI parameters from FDT:
[ 0.000000] EFI v2.40 by American Megatrends
[ 0.000000] efi: ACPI 2.0=0x807ff43000 ESRT=0x807e161e18 SMBIOS 3.0=0x807e161c18
[ 0.000000] Moving initrd from [4079b0f000-407ac457c3] to [7e0ac9000-7e1bff7c3]
[ 0.000000] Unhandled fault: synchronous external abort (0x96000010) at
0xffffffbffe63e078
[ 0.000000] Internal error: : 96000010 [#1] SMP
[ 0.000000] Modules linked in:
[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.6.0-1-arm64 #1
Debian 4.6.2-2
[ 0.000000] Hardware name: Gigabyte X-Gene MP30-AR0 board (DT)
[ 0.000000] task: ffffff8008b88800 ti: ffffff8008b78000 task.ti:
ffffff8008b78000
[ 0.000000] PC is at __memcpy+0x100/0x180
[ 0.000000] LR is at copy_from_early_mem+0x6c/0x94
etc.
I suspect that the "ConvertPages: Incompatible memory types" (which comes
from UEFI) may be the fundamental issue, but I'm not certain.
I've tried various different Debian installer images with the same result;
I'll look at what Linaro / Ubuntu / etc. have next. (Suggestions?)
More important question - where are the people who understand this stuff?
Debian-EFI? Linaro? APM? Gigabyte?
Thanks, Phil.