RPi4+UEFI/ACPI---how to choose root partition?

[Paul Mather <bsd-lists%gromit.dlib.vt.edu@localhost>]

I have a Raspberry Pi 4 8GB model on which I have installed NetBSD/aarch64 -CURRENT.  I am using the UEFI/ACPI firmware at https://github.com/pftf/RPi4/releases/tag/v1.16 (i.e., RPI_EFI.fd) to boot rather than using the standard bootcode.bin.

Following a recent post by Mark Millard (https://mail-index.netbsd.org/port-arm/2020/07/01/msg006833.html), I moved my NetBSD installation to an external USB3 SSD and wish to run from that.  I'm using the "stock RPi4 eeprom firmware" option described in Mark's message, with the https://github.com/pftf/RPi4/releases/tag/v1.16 related materials on the SD card.  This allows the UEFI/ACPI firmware to load and then boot NetBSD from the external USB3 SSD.

This MOSTLY works for me.  I've selected the EFI partition on the external USB3 SSD to boot from by default in the UEFI settings.  When it boots, I can see it loads the "netbsd.img" loader.  It then fails to load/boot the "netbsd" kernel itself (after trying all the various options, e.g., netbsd, netbsd.gz, onetbsd, onetbsd.gz, ..., etc.).  It appears this is because it is trying to load it (in my case) from hd1b: whereas my root file system is actually on hd1e:.  I am able to boot successfully by executing "boot hd1e:netbsd" from the loader prompt.

Is there any way of specifying which partition to boot "netbsd" from, or does it always look in "hd?b:"?

On a RPi3 system running NetBSD/aarch64 9-STABLE, I set "root=wedge:system" in cmdline.txt on the EFI partition to boot "netbsd" from my root partition (i.e., from the GPT partition labelled "system").  Is there something similar I can do with the UEFI/ACPI boot firmware?  (It appears to ignore "cmdline.txt".)

I don't have much familiarity/experience with UEFI booting/configuration, so apologies if the answer is something obvious. :-)

Cheers,

Paul.