This was the culprit. So, even though I already troubleshooted missing kmods by installing all the mt-related opkg packages, I am not sure why it didn't work the last time. Anyhow, installed kmod-mt76x0e, rebooted & 802.11ac module appeared.
Thank you for your efforts in helping me (and any other future community member who will be an owner of this device model) troubleshoot the device support.
Now, everything needs to be documented, wiki docs written, PR created (containing updated makefile(s), DTS(I) & tplink-safeloader), and the device will become supported.
Also, how would I go about fixing the kernel partition layout, as indicated by a warning / error message in the boot log?
3 Likes