Serial UART does not work with downstream RPi kernel

[ElvishJerricco]

The pi's firmware and EDK2 both output over serial like normal. But when the RPi downstream linux kernel boots, it fails to set up the serial console. The "System Table Mode" is set to "Device Tree."

With their linux 6.1 branch, it logs this:

$ dmesg | grep -i uart
[    0.012261] Serial: AMBA PL011 UART driver
[    0.375564] bcm7271-uart 107d50c000.serial: unable to register 8250 port
[    0.375575] bcm7271-uart: probe of 107d50c000.serial failed with error -28

With their 6.9 branch, I get a very similar log:

$ dmesg | grep -i uart
[    0.011473] Serial: AMBA PL011 UART driver
[    0.303985] bcm7271-uart 107d50c000.serial: error -EINVAL: unable to register 8250 port
[    0.304006] bcm7271-uart 107d50c000.serial: probe with driver bcm7271-uart failed with error -22

There is a /dev/ttyAMA10 device, but doesn't seem to work. Nothing happens after running systemctl start serial-getty@ttyAMA10.service.