no console during boot on UC20

[Oliver Grawert]

when booting UC20 on a Pi4 the screen backlight is completely off and no signal is produced.

inspecting the boot a little closer it seems the necessary modules for bringing up the vc4 framebuffer are not included in the initramfs on ubuntu core. once they get loaded (after boot) the backlight and signal turn on. The initrd should include the modules and load them during boot.

this is also required to bring any kind of bootsplash back to UC20 which is a reason all our digital signage customers currently hold back on going forward to UC20.

the modules required are:

ogra@ubuntu:~$ lsmod|grep vc4
vc4 290816 3
drm_kms_helper 225280 3 vc4
snd_soc_core 262144 1 vc4
snd_pcm 143360 5 vc4,snd_bcm2835,snd_soc_core,snd_pcm_dmaengine
drm 565248 7 gpu_sched,drm_kms_helper,v3d,vc4

the loading during boot in the journal is shown below:

ogra@ubuntu:~$ sudo journalctl -b | grep vc4
Apr 01 17:23:45 ubuntu kernel: vc4-drm gpu: bound fe600000.firmwarekms (ops vc4_fkms_ops [vc4])
Apr 01 17:23:45 ubuntu kernel: fb0: switching to vc4drmfb from simple
Apr 01 17:23:45 ubuntu kernel: [drm] Initialized vc4 0.0.0 20140616 for gpu on minor 1
Apr 01 17:23:45 ubuntu kernel: vc4-drm gpu: fb0: vc4drmfb frame buffer device

[Juerg Haefliger (juergh)]

The list of modules to include in the initrd is not under the kernel's control but ubuntu-core-initramfs. This commit should fix the issue:

https://github.com/snapcore/core-initrd/commit/fa088d26aded1a8c8ce9910ccdb81ba99ed976c4