Possible to use QEMU’s VNC feature with simpledrm and the DRM fbdev emulation layer?

[Paul Menzel]

Dear QEMU folks,


I wanted to replace replace the fbdev drivers with simpledrm and the DRM 
fbdev emulation layer [1][2].

My colleagues now noticed, that QEMU’s VNC feature does not work anymore 
for the console [3]. We are using QEMU emulator version 7.2.0. Log 
differences:

Working (CONFIG_FB=y):

    [    0.000000] Linux version 6.5.2.mx64.428-00118-g2bb542eff7d5 
(buczek@dose.molgen.mpg.de) (gcc (GCC) 10.4.0, GNU ld (GNU Binutils) 
2.41) #49 SMP PREEMPT_DYNAMIC Fri Sep  8 11:29:40 CEST 2023
    […]
    [    1.774569] bochs-drm 0000:00:02.0: vgaarb: deactivate vga console
    [    1.881464] Console: switching to colour dummy device 80x25
    [    1.882069] [drm] Found bochs VGA, ID 0xb0c5.
    [    1.883935] [drm] Framebuffer size 16384 kB @ 0xfd000000, mmio @ 
0xfebd0000.
    [    1.885523] [drm] Found EDID data blob.
    [    1.886042] [drm] Initialized bochs-drm 1.0.0 20130925 for 
0000:00:02.0 on minor 0
    [    1.888123] fbcon: bochs-drmdrmfb (fb0) is primary device
    [    1.895255] Console: switching to colour frame buffer device 160x50
    [    1.901041] bochs-drm 0000:00:02.0: [drm] fb0: bochs-drmdrmfb 
frame buffer device

Non-working (CONFIG_FB unselected):

    [    1.753182] bochs-drm 0000:00:02.0: vgaarb: deactivate vga console
    [    1.760518] Console: switching to colour dummy device 80x25
    [    1.761660] [drm] Found bochs VGA, ID 0xb0c5.
    [    1.762618] [drm] Framebuffer size 16384 kB @ 0xfd000000, mmio @ 
0xfebd0000.
    [    1.766553] [drm] Found EDID data blob.
    [    1.767442] [drm] Initialized bochs-drm 1.0.0 20130925 for 
0000:00:02.0 on minor 0


Kind regards,

Paul


[1]: https://fedoraproject.org/wiki/Changes/ReplaceFbdevDrivers
[2]: https://github.molgen.mpg.de/mariux64/linux/commits/mariux-6.1.39-450
[3]: 
https://github.molgen.mpg.de/mariux64/linux/commit/f3ba607af9fca65ae01cfee6ed29b6946f059f11