Re: [PATCH 1/1] hw/display: Support per-head resolutions with virtio-gpu

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Aug 27, 2025 at 11:48:34AM -0400, Andrew Keesler wrote:
> Sending again (replying all this time).
> 
> > IIUC from the current code, xres/yres are only set against the
> > first head. The 2nd and later heads are left undefined by the
> > virtio-gpu-base code at least - I'm unclear if something else
> > in QEMU will fill in defaults later, or if they set to 0x0.
> 
> That is correct - xres/yres are only set against the first head in the
> current code. The wording in my commit message (and cover letter) was
> misleading. I will fix that to say that "If no
> virtio_gpu_base_conf.outputs are provided,
> virtio_gpu_base_conf.xres/virtio_gpu_base_conf.yres will still be
> respected _for the first head_ for backwards compatibility".
> 
> The only way I could get QEMU to fill in xres/yres for a 2nd and later
> head was to trigger virtio_gpu_ops.ui_info via a VNC client.
> 
> > Is it relevant to set xres/yres on outputs, even when they are
> > not (yet) enabled ?  Perhaps we should have an explicit 'enabled: bool'
> > property in the 'outputs' struct ?
> 
> Maybe you might want to set xres/yres on an output, but not enable it
> yet? I don't have any concrete examples of when you might want to do
> that, maybe you have some examples?

No, I don't have an example.

> I feel like I could see a user setting xres/yres on an output,
> forgetting to set enabled on that output, and then being confused why
> their head is blank. Because of this, my vote would be to default to
> enabling an output when it has configuration. I am easily swayed by
> your guidance, though.

Ok, lets just document that setting xres/yres will cause the
output to be automatically enabled. We can always retrofit
an 'enabled' property at a later date if someone arrives with
a use case for setting res without enabling the output.

With regards,
Daniel
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