Comment 7 for bug 2064370

> If I switch to the KMS overlay, the message is exactly the same, so it means the EDID is accessible from the monitor in either case.

Not quite the case I'm afraid. The output you're quoting there is from the pi's bootloader running on the GPU. So, what you've established there is that the GPU (which ignores hotplug, as noted in 6by9's comment in the upstream bug) reads the EDID. This is all that's needed in the FKMS case because there the kernel driver is a thin shim that just talks to the firmware running on the GPU and retrieves EDID data from there.

However in the KMS case, the bootloader eventually relinquishes control of the GPU to the linux kernel, and the kernel then attempts to retrieve the EDID independently (as least, this is my understanding of things -- I'm no expert in this area; corrections welcome!).

Glad to hear the force_hotplug option works; that largely gels with the idea that the monitor is not correctly asserting hot-plug. If it's not asserting hot-plug on boot, the would also explain why re-plugging the monitor doesn't work either. FKMS doesn't care, it just reads the EDID anyway, but the KMS driver is waiting for a signal to do so and there's none on boot, or later when the monitor is re-plugged.