I'm trying to use Fedora 28 Minimal on a Raspberry Pi 3 to set up an NTP server using a GPS hat, specifically intended for this purpose:
https://www.tindie.com/products/nsayer/skytraq-venus838lpx-t-timing-gps-module-breakout/

(That link initially shows the non-Raspberry Pi version; click the second photo for the Pi version.)

Booting Fedora from the MicroSD fails, apparently due to U-Boot thinking that the UART has "pressed a key" to abort the boot. I get a U-Boot prompt, followed by lots of garbage (presumably due to baud rate mismatch).

Is there any easy way to get U-Boot to not listen to the UART?

I've tried this with 32-bit and 64-bit Fedora 28 on a Pi 3B and a Pi 3B+, with the same results. Without hte GPS hat it boots fine.

Thanks!

Best regards,
Eric