I have verified that enabling the bochs-drm kernel module on bionic does not cause any regressions for PowerKVM machines when the video device is VGA=std.

TLDR: See Screenshot: https://launchpadlibrarian.net/475658598/Screenshot%20from%202020-04-22%2015-14-13.png

This is in response to the main cause of regression concern, LP #1378648, which got bochs-drm disabled in the first place, on yakkety.

On Christian's advice, I created a ppc64el instance on Canonistack, with the m1.medium flavor and c8c120bd-3d55-4e2d-8cc5-93039a62524f image (ubuntu/ubuntu-bionic-18.04-ppc64el-server-20200407-disk1.img).

From there, I installed the KVM packages and a xfce4 desktop, and got xrdp working. I then installed virt-manager.

I modprobed the kvm_pr kernel module on my instance to enable nested kvm on ppc64el.

From there, I installed Ubuntu 18.04.4 Server ppc64el, using virt-manager. The "Machine Type" was pseries-2.12, and the Video Model was set to "VGA" [1].

[1]: https://launchpadlibrarian.net/475658622/Screenshot%20from%202020-04-22%2015-14-04.png

Upon booting, the system was using the Open Firmware frame buffer:

[    0.888072] Using unsupported 800x600 vga at 200081000000, depth=32, pitch=3200
[    0.890480] Console: switching to colour frame buffer device 100x37
[    0.892181] fb0: Open Firmware frame buffer device on /pci@800000020000000/vga@6

$ cat /proc/fb
0 OFfb vga

Which is what LP #1378648 wanted.

I then enabled my ppa where my test packages were built:

https://launchpad.net/~mruffell/+archive/ubuntu/sf272653-test

and installed new kmod and 4.15.0-96-generic test builds with bochs-drm enabled in the kernel config, and removed from the kmod blacklist.

I then rebooted, and found that system boots successfully, and does not get hung up at the bug in LP #1378648, indicating that it has been fixed before 4.15.

I checked "lsmod" and bochs-drm has been loaded, and looking at dmesg, initially the Open Firmware frame buffer device is used, and later in the boot, bochs-drm is loaded, and takes over the frame buffer.

See screenshot [2] for proof that bochs-drm is running and functions correctly in virt-manager.

[2]: https://launchpadlibrarian.net/475658598/Screenshot%20from%202020-04-22%2015-14-13.png

A complete dmesg from this boot can be found here [3].

[3] https://paste.ubuntu.com/p/Q8V7fKnRzz/

Interesting parts:

[    0.893046] Using unsupported 800x600 vga at 200081000000, depth=32, pitch=3200
[    0.895482] Console: switching to colour frame buffer device 100x37
[    0.897270] fb0: Open Firmware frame buffer device on /pci@800000020000000/vga@6
...
[    2.041835] checking generic (200081000000 1d4c00) vs hw (200081000000 1000000)
[    2.041836] fb: switching to bochsdrmfb from OFfb vga
[    2.042568] Console: switching to colour dummy device 80x25
[    2.045581] [drm] Found bochs VGA, ID 0xb0c5.
[    2.046100] [drm] Framebuffer size 16384 kB @ 0x200081000000, mmio @ 0x200082000000.
[    2.058141] [TTM] Zone  kernel: Available graphics memory: 504512 kiB
[    2.058883] [TTM] Initializing pool allocator
[    2.059372] [TTM] Initializing DMA pool allocator
[    2.074890] Console: switching to colour frame buffer device 128x48
[    2.089805] bochs-drm 0000:00:06.0: fb0: bochsdrmfb frame buffer device
[    2.090549] [drm] Initialized bochs-drm 1.0.0 20130925 for 0000:00:06.0 on minor 0

$ cat /proc/fb
0 bochsdrmfb

With good dmesg outputs, and positive test results in virt-manager, I am happy to say that enabling bochs-drm will not cause any regressions on ppc64el, and with that, I hope it satisfies your request for testing.