RPi3 start.elf regression: garbled serial, broken USB in UEFI

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
25/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
raspberry-pi

Research direction

Start by comparing the v1.22 RPi3 release with the latest VPU start and fixup files, following the reproduction steps in the issue. Review the UEFI Tiano Core mbox clock query and the linked pftf/RPi3 issue while checking UART and DWC2 USB behavior. Done means the firmware regression is explained and working serial and USB behavior is restored or the incompatibility is documented.

Written by the indexing model from the issue text.

Description

This was seen in UEFI (Tiano Core) build for RPi3 with the latest VPU firmware. Symptoms: garbled UART output and DWC2 USB2 stopped working. Now, for USB the UEFI fw was querying mbox interface for the reported clock, so this could mean the reported clock was wrong.

Tracked https://github.com/pftf/RPi3/issues/15

To reproduce: Grab latest (v1.22) release from https://github.com/pftf/RPi3/releases. It should boot with working USB and non-garbled UART. Now replace the VPU bits (start + fixup) with your latest. See USB not working, see garbled UART.

Could someone explain why we might be seeing this behavior?

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