Not much you can do except use the stock FW
Build has been updated.. Flashing is now in-line with other ipq807x devices - just boot to initramfs and apply the sysupgrade. This will take over the empty "reserved" partition to offer 279Mb on rootfs.
I acquired a GS110MX switch and gave it try after applying the DTS corrections you identified. Seems to be working on my end. I had some trouble setting the speed directly but it worked with the advertise parameter's.
aq-fw-download /lib/firmware/AQR-G3_v4.3.C-AQR_DNI_DR-EQ35AX8-R-prov1_ID23888_VER1311.cld lan5 7 ethtool -s lan5 advertise 0x1000000000000 ssdk_sh debug phy set 7 0x4004c441 0x8
From what branch are you compiling it? I tried your
ipq807x-5.15-pr branch, commit 60734a8404cb. And
ethtool eth4 as example doesn't work. I'm on the wrong branch?
ipq807x and ~7 ipq807x devices just got officially added to master. Hopefully once the DTS is figured out the RAX120 could be the 8th addition to master. With the 8x8 5ghz antennas and multi-gig port it should be one of the more / most powerful all-in-one options out there for OpenWrt.
You have the right branch but the interface names changed. lan5 is the AQR.
I may have forgot to apply your port id correction. Not sure how I missed that. I'll get another update in shortly now that ipq807x-5.15-pr has been merged.