panic sdhci_bcm0-slot0 controller timeout when HDMI not attached

Hi,

context is 13.0-ALPHA1 #0 main-c255963-g54c743e5b29 with custom no-debug
kernel

I have an rpi4/8GB which boots off sdcard. It has an attached usb3 disk
which is ZFS and has the data. The guts of the OS is on the sdcard though.
It's been working fine up till a week or so ago when I decided to 
update FreeBSD. On reboot it failed to come back. It normally
runs headless and keyboardless.

I found that the machine would boot normally *only* if a screen was plugged
into the HDMI port. If the screen was disconnected, console output revealed 
eventual drop to debugger a short while after:

sdhci_bcm0-slot0: Controller timeout

(In the output there is also "Root mount waiting for: CAM" but this is 
deliberate and is there to allow usb3 to wake up before ZFS)

The controller never times out if HDMI is attached. I thought at first
it also needed a keyboard but that's not the case.

boot failure: 
https://cloud.zyxst.net/~john/FreeBSD/current/rpi4b/badboot.txt

successful boot:
https://cloud.zyxst.net/~john/FreeBSD/current/rpi4b/goodboot.txt

thanks,   
-- 
J.

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