Re: [gentoo-user] Virtual Desktop with a Virtual Monitor?

[Mark Knecht <markknecht@gmail.com>]

On Sun, Nov 7, 2021 at 2:04 PM Wol <antlists@youngman.org.uk> wrote:
>
> On 07/11/2021 20:39, Mark Knecht wrote:
> > Hi,
> >     I've been playing with a Raspberry Pi 4 as a utility divice for a
> > couple of purposes - a backup server for here at home as well as an
> > astrophotography manager to run my camera and mount. So far everything
> > is fine when I have a monitor attached. I can ssh in and run X apps,
> > and I can run the VNC client and control the desktop.
> >
> >     What I find, however, is that when I boot the RP4 without the
> > monitor attached, which I would be doing most all the time, I lose the
> > desktop functionality through VNC. I can still ssh X apps, and both
> > xdpyinfo and xrandr still say the X resolution is 1920 x 1280, but
> > there doesn't appear to be a real desktop for VNC to latch onto.
> >
> >     I get that this must be possible as essentially VirtualBox is able
> > to do this. I wonder if there's a way for mere mortals to do something
> > similar?
> >
> I'm guessing the reason there isn't a virtual desktop is because
> nobody's logged in AT THE PI and started one!
>
> Just start Xorg over ssh, or plasma-wayland, or whatever. Sorry I don't
> (yet) know how to do it, I need to find out because I want to do exactly
> the same :-)
>
> Cheers,
> Wol
>

It seems so far that it's even a little more onerous than that:

In the case where the monitor is detached at boot two modules are not
loaded - fuse & nvmem_rmem. Other than that the module list appears
identical.

If I ssh into the RP4 when it's running RPi OS (previously called
Raspbian apparently) but with the monitor DISCONNECTED when I boot
then screenfetch says there's no GPU. Plugging in the monitor after
it's booted doesn't change anything:

mark@science:~$ ssh -X pi@192.168.86.84
pi@192.168.86.84's password:
Linux raspberrypi 5.10.63-v7l+ #1459 SMP Wed Oct 6 16:41:57 BST 2021 armv7l

<SNIP>
pi@raspberrypi:~ $ screenfetch -nN
pi@raspberrypi
OS: Raspbian 10 buster
Kernel: armv7l Linux 5.10.63-v7l+
Uptime: 0m
Packages: 2038
Shell: 723
Resolution: 5760x1080
DE: KDE5
WM: KWin
CPU: ARMv7 rev 3 (v7l) @ 4x 1.5GHz [29.6°C]
GPU:
RAM: 61MiB / 7898MiB

pi@raspberrypi:~ $ lspci -vm -k
Device: 00:00.0
Class:  PCI bridge
Vendor: Broadcom Limited
Device: Device 2711
Rev:    10
Driver: pcieport

Device: 01:00.0
Class:  USB controller
Vendor: VIA Technologies, Inc.
Device: VL805 USB 3.0 Host Controller
SVendor:        VIA Technologies, Inc.
SDevice:        VL805 USB 3.0 Host Controller
Rev:    01
ProgIf: 30
Driver: xhci_hcd

pi@raspberrypi:~ $

However, booting with the monitor ATTACHED now shows the GPU, or at
least a DRM framebuffer possibly, in screenfetch. The PCI devices are
the same:

pi@raspberrypi:~ $ screenfetch -nN
 pi@raspberrypi
 OS: Raspbian 10 buster
 Kernel: armv7l Linux 5.10.63-v7l+
 Uptime: 0m
 Packages: 2038
 Shell: 935
 Resolution: 3840x1080
 DE: KDE5
 WM: OpenBox
 CPU: ARMv7 rev 3 (v7l) @ 4x 1.5GHz [37.9°C]
 GPU: vc4drmfb
 RAM: 144MiB / 7898MiB
pi@raspberrypi:~ $

pi@raspberrypi:~ $ lspci -vm -k
Device: 00:00.0
Class:  PCI bridge
Vendor: Broadcom Limited
Device: Device 2711
Rev:    10
Driver: pcieport

Device: 01:00.0
Class:  USB controller
Vendor: VIA Technologies, Inc.
Device: VL805 USB 3.0 Host Controller
SVendor:        VIA Technologies, Inc.
SDevice:        VL805 USB 3.0 Host Controller
Rev:    01
ProgIf: 30
Driver: xhci_hcd

pi@raspberrypi:~ $

I will repeat this experiment using Ubuntu in a little while to see if
the missing GPU is an OS or hardware thing. In this hardware it looks
like the GPU hardware is behind the PCI bridge.

Still to look into Neil's x2go suggestion.

Mark