Newer revisions of the RPi4 need their xHCI chip, VL805, firmware to be loaded explicitly. Earlier versions didn't need that as they where using an EEPROM for that purpose. This series takes care of setting up the relevant infrastructure and run the firmware loading routine at the right moment.
Patch 2 is a little invasive, but I couldn't find a mechanism in u-boot similar to Linux's PCI quirks.
Nicolas Saenz Julienne (2): arm: rpi: Add function to trigger VL805's firmware load usb: xhci: Load Raspberry Pi 4 VL805's firmware
arch/arm/mach-bcm283x/include/mach/mbox.h | 13 +++++++ arch/arm/mach-bcm283x/include/mach/msg.h | 7 ++++ arch/arm/mach-bcm283x/msg.c | 41 +++++++++++++++++++++++ drivers/usb/host/xhci-pci.c | 6 ++++ 4 files changed, 67 insertions(+)