The problem is that hotplug doesn’t work, which means that if the monitor doesn’t respond early enough in the boot, then the HDMI will never turn on.
I’d like to tell it to turn on the HDMI regardless of whether or not some monitor has been detected.
I’m currently using video=HDMI-A-1:1280x800@60 , which is unfortunately not sufficient.
Edit: also tried using video=HDMI-A-1:1280x800R@60e – still no, despite this;
# cat /sys/class/drm/card0-HDMI-A-1/enabled < enabled