Using generic fbdev helpers breaks hibernation

Maybe someone more familiar with the generic drm fbdev helpers can help me understand why they don't work with hibernation, at least with AMD GPUs. We converted amdgpu to use the generic helpers instead of rolling our own in this patch[1], but it seems to have broken hibernation[2]. amdgpu has always set mode_config.prefer_shadow = 1, but that seems to be the cause of the hibernation breakage with the generic helpers. I've been staring at the code for a while now but I can't see why this fails. Any pointers?

Thanks,

Alex

[1] - https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... [2] - https://bugzilla.kernel.org/show_bug.cgi?id=216119