Raspberry pi 4B (4GB RAM) with HDMI not connected fails to boot using newer release

Compare firmware package commits dd8cbec5a6d27090e5eb080e13d83c35fdd759f7 and 62fc8c01165a80021054a430182b504f7b877c2d on the Raspberry Pi 4B, using the reported config.txt and cmdline.txt. Reproduce booting with power and Ethernet but no HDMI, then check whether the board boots and remains reachable over the network without a display.

Describe the bug

Using Arch Linux Arm (64-bit) with a 4.19.71-v8+ kernel boots fine when using the firmware package 20200412 (this is commit dd8cbec5a6d27090e5eb080e13d83c35fdd759f7) with nothing connected to the HDMI ports, but when using package 20200528 (commit 62fc8c01165a80021054a430182b504f7b877c2d), the board will only boot up successfully if there is a monitor connected to one of the HDMI ports.

What happens in this state is also odd, the board has an ethernet cable connected and when it boots successfully, the green and orange lights come on and the board is reachable over the network, however when it boots without the monitor connected, the green ethernet light remains off but the orange light comes on and the board is dead to the network.

To reproduce

I only have 1 board and 1 SD card so haven't tried reproducing it freshly. How it happens on my board is I have arch linux arm (64-bit) installed, I also have a custom built 4.19.71-v8+ kernel (I upgraded to 5.4 and was seeing issues so went back to 4.9). I upgraded all packages and rebooted (just power and ethernet connected), at this point the board is basically dead.

In my config.txt is:

gpu_mem=64
kernel=kernel8.img
dtparam=i2c_arm=on
arm_64bit=1

In my cmdline.txt is:

console=ttyS0,115200 console=tty0 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=bfq rw rootwait dwc_otg.speed=1 dwc_otg.host_support_fs_ls_low_power=1 dwc_otg.host_ls_low_power_phy_clk=1 dwc_otg.fiq_fix_enable=1

Expected behaviour

Board should boot up fine regardless if HDMI is connected or not, and ethernet should also work.

Actual behaviour

Board does not appear to boot up, orange light on ethernet is on whilst yellow is off, board is unresponsive over network, if HDMI is plugged in after this point then nothing appears on the screen, if a USB keyboard is plugged in and caps lock is pressed, the caps lock light never illuminates.

System

Model: Raspberry Pi 4B (4GB)
OS: Arch Linux Arm 64-bit
Firmware: Apr  7 2020 15:56:30 version 6ab498ee82102a9669a1909ae90341e3ecc2128f (clean) (release) (start)
Kernel: Linux BRPi 4.19.71-v8+ #1 SMP Sun Sep 8 14:10:58 BST 2019 aarch64 GNU/Linux