Re: qemu and -vga vs. -device

[Gerd Hoffmann]

On Sat, Sep 24, 2022 at 12:12:45AM -0700, Adam Williamson wrote:
> On Mon, 2022-09-19 at 06:42 +0200, Gerd Hoffmann wrote:
> > On Fri, Sep 16, 2022 at 10:02:17AM -0700, Adam Williamson wrote:
> > > Hi Gerd!
> > > 
> > > I'm working on a patch to revise how openQA sets video devices in qemu.
> > > In that context, a question: if we always want to specify a single
> > > video device with `-device` (e.g. `-device VGA` or `-device virtio-
> > > vga`), should we also specify `-vga none` to ensure qemu doesn't also
> > > include another adapter as a default for the -vga arg?
> > 
> > Doesn't hurt to include it.  In theory it should not be needed, qemu has
> > a list of vga devices and in case '-device $vga' is found on the command
> > line will turn off the default vga device automatically.  In practice
> > there are qemu versions where this list is not complete, so it
> > sometimes doesn't work as intended.
> > 
> > Alternatively use '-nodefaults' which will disable all automatically
> > added devices (vga, nic, cdrom, ...).
> 
> Thanks Gerd!
> 
> So, I got around to testing this today, and found something
> interesting. On ppc64le, adding `-vga none` seems to break things.
> Booting a Fedora installer ISO, which should show the boot menu with a
> 60 second timeout then boot to the installer, if we run the VM with `-
> vga std`, we see the bootloader. If we run it with `-device VGA` and no
> `-vga` arg, we see the bootloader. But if we run qemu with `-vga none -
> device VGA`, we don't see the bootloader. The system just sits at the
> OFW init screen apparently forever (I thought it might actually be
> running in the background and recover to anaconda after the 60 second
> boot timeout, but it doesn't seem to).
> 
> Not sure what's going on there, but thought you might be interested.

Hmm, no clue offhand.  Cc'ing qemu-ppc list (+ keeping full context).

I know ppc has some vga quirks in the machine init code path, switching
framebuffer byteorder to bigendian for example, maybe more.  Possibly
something goes wrong there.

take care,
  Gerd