Success!!
I applied my newly revised patches to 76ac1d3918f91b9234cfb26c6519da0cf5f86302 on the wip-pinebook-pro branch.
u-boot correctly finds the rk3399-pinebook-pro.dtb file.
The extlinux.conf file no longer needs to be altered. It is as follows:
# This file was generated from your Guix configuration. Any changes
# will be lost upon reconfiguration.
UI menu.c32
MENU TITLE GNU Guix Boot Options
PROMPT 1
TIMEOUT 50
LABEL GNU with Linux-Libre-Pinebook-Pro 5.6.0
MENU LABEL GNU with Linux-Libre-Pinebook-Pro 5.6.0
KERNEL /gnu/store/qs1292ckhvkprsgdyxq665qj167l5c07-linux-libre-pinebook-pro-5.6.0/Image
FDTDIR /gnu/store/qs1292ckhvkprsgdyxq665qj167l5c07-linux-libre-pinebook-pro-5.6.0/lib/dtbs
INITRD /gnu/store/2d01lxl21i74jflji5smi9fhwsgyqanf-raw-initrd/initrd.cpio.gz
APPEND --root=/dev/mmcblk1p1 --system=/gnu/store/453h9sqcqvnpj72k0gwia3zsfavhar4p-system --load=/gnu/store/453h9sqcqvnpj72k0gwia3zsfavhar4p-system/boot ethaddr=${ethaddr} eth1addr=${eth1addr} serial=${serial#} video=HDMI-A-1:1920x1080@60 video=eDP-1:1920x1080@60 vga=current
The FDTDIR /gnu/store/qs1292ckhvkprsgdyxq665qj167l5c07-linux-libre-pinebook-pro-5.6.0/lib/dtbs still has a rockchip sub-folder that contains the rk3399-pinebook-pro.dtb file.
I decided to go back to my older SD card and remove the rockchip from the FDTDIR path, and it also booted.
I know previously that janneke and I had problems with this, but obviously along the way something was fixed.
At any rate, it’s nice to see the image boot and no longer having to edit the extlinux.conf file.
I will have to put together a patch set in the near future.
Cheers!
Brian C. Woodcox