[vbox-dev] Linux guest: two framebuffer devices? Is it possible?

[Jan Petrouš]

Hi Michael.

> On 6 September 2016 at 11:13, Michael Thayer <michael.thayer at oracle.com>
wrote:
> >
> > Hello Jan,
> >
> > I think you asked about this on IRC yesterday.  The first file that you
mention is part of the Linux drm driver (the rest is the other files in
that folder).  I wrote the driver, based on in-kernel ones, but I am not an
expert in the kernel drm subsystem, and in particular I only use the basic
kernel fbdev translation functions to provide the framebuffer driver.  You
would probably be better asking on the dri-devel list<1> about what to
change to get one fbdev device per head.  You might be in luck and there
might be a simple solution.
> >
>

I just get some patches which adds to the linux vboxvideo.ko support for
multiframebuffer (one framebuffer per display).
But I have some very strange trouble with it.

When started, only the first framebuffer is working (and so only one
graphical display is enabled).
Then I enable second FB by entering "fbset -ifb /dev/fb1 -accel 1".
An that moment, I get the virtual machine freezed. Now if I try to send
[ENTER] or any other key,
I don't see cursor or any ather activities on the command line (on guest
Linux system).

The strangeness is that if I click on close button of guest console window
(so the popup menu starts
with option of save, shutdown or power-off), the windows title changed to
"paused" and only now I can see
the previously entered keys showed on guest console. It looks like console
lock is released when
popup windows started and again acquired if I cancel popup.

It looks like the guest console (fbcon?) gets freezed (so locked) by some
initialization task inside
the modified vboxvideo driver.

Configuration:

Host system: Fedora 24 desktop with kernel 4.6.7, but my colleague tries
that on Windows 7, the issue is the same,
so I guess it is host system independetend issue
Guest: I tried two distros, both have installed minimal packages and no Xwin
Guest1: Fedora 24 desktop, kernel 4.6.7
Guest2: Arch latest, kernel 4.7.2

Do you have any idea how to debug such console freeze?

/Jan

> Yes, I was asking on irc, but I think I fallen in lunch mode there, so
only silence :)
> That is why I asked here again.
>
> Anyway, thanks for the hints! I definitely will have a try with drm.
>
> But it's good that the author of driver is reachable.
> So more questions can come later ;)
>
> CU
> /Jan
>
>
> > Regards,
> >
> > Michael
> >
> > <1> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
> >
> > On 05.09.2016 17:42, Jan Petrouš wrote:
> >>
> >> Hi,
> >>
> >> as VirtualBox supports dual head config I was trying to start two
> >> framebuffers on it.
> >> But unsucessfull.
> >>
> >> The main constraint is that guest Linux is very tiny and has no
> >> X-Windows inside.
> >> The application requires only the framebuffer devices.
> >>
> >> I did many hours googling to find solution but I found only solution
for
> >> xwin environment.
> >>
> >> Is it even possible to enable two FB devices on dualhead configuration?
> >>
> >> If the answer is NO, can you show me where I should start to look
inside
> >> the sources?
> >>
> >> I found the VB Additions subversion repo where are at least two video
> >> drivers:
> >>
> >> 1,
> >>
http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Additions/linux/drm/vbox_fb.c
> >> 2,
> >>
http://www.virtualbox.org/svn/vbox/trunk/src/VBox/Additions/x11/vboxvideo/vboxvideo.c
> >>
> >> I guess that the driver for my non-x11 environment is the first one. Is
> >> it true?
> >>
> >> I'm rather linux video driver noob, but I would like to get some good
> >> start point
> >> where I can at least try to start with.
> >>
> >> BR.
> >> /Jan
> >>
> >> PS: Installed Fedora Server 24 Minimal config, so kernel is 4.6.7
> >>
> >>
> >> _______________________________________________
> >> vbox-dev mailing list
> >> vbox-dev at virtualbox.org
> >> https://www.virtualbox.org/mailman/listinfo/vbox-dev
> >>
> >
> > --
> > Michael Thayer | VirtualBox engineer
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