Did you check if everything needed is enabled in your configuration and if the keyboard is detected after a usb start / usb tree ?
It is detected, yes.
I believe the configuration is fine; I see this issue using the standard "pinebook-pro-rk3399_defconfig" and building either from the latest commit in git or from the tree at commit 3a5771249 (Peter's, which he mentioned earlier).
Changing the configuration to remove the XHCI and EHCI drivers, or to add the Inno USB phy driver, doesn't help.
Beyond that, for BL31 I'm using a release build of v2.3 of the ARM Trusted Firmware. I've tested using debug and release builds of v2.3 and v2.2 without seeing a difference.
I believe I have 2.3 from upstream.
Your keyboard is working with linux, right ?
Yes it is. It's only U-Boot that's affected.
The only things I've thought of so far that might be unique about my setup are
My PBP is from the latest manufacturing run of a few months ago, not last year's; and
I currently have the eMMC module disabled via the internal switch and am booting off a microSD card.
I'm booting off mSD and I actually took out the eMMC because it was a pain dealing with it when I was developing the upstream U-Boot support. I think my keyboard firmware is quite old (dealing with that is on my list), but I'm not sure that should make a difference here.