vfio: add vgpu edid support?

[Zhang, Tina]

> -----Original Message-----
> From: Gerd Hoffmann [mailto:kraxel at redhat.com]
> Sent: Monday, September 10, 2018 6:35 PM
> To: Zhang, Tina <tina.zhang at intel.com>
> Cc: intel-gvt-dev at lists.freedesktop.org; kvm at vger.kernel.org; Kirti Wankhede
> <kwankhede at nvidia.com>; Alex Williamson <alex.williamson at redhat.com>
> Subject: Re: vfio: add vgpu edid support?
> 
>   Hi,
> 
> > > Intel has two hard-coded edid blobs for that (depending on vgpu type).
> > > Not sure how nvidia handles this, but probably simliar.  With qemu
> > > passing a edid blob for the virtual display instead of using the
> > > hardcoded blob we could make the display configuration much more flexible.
> >
> > Sounds interesting. People are asking us to add more display modes.
> > With this proposal, we could provide any required mode in a flexible way.
> 
> Yes, exactly.
> 
> > But the hard-coded resolution might still be needed. As it is used for
> > vgpu resources allocation during vgpu creation before running a qemu.
> > And a vgpu cannot support a resolution bigger than the one used for
> > its resources allocation.
> 
> The CAPS ioctl below should handle that:
> 
> > > +/**
> > > + * VFIO_DEVICE_GFX_EDID_CAPS - _IOW(VFIO_TYPE, VFIO_BASE + 17,
> > > + *                                  struct vfio_device_gfx_edid_caps)
> > > + *
> > > + * Get edid capabilities.
> > > + *
> > > + * Drivers must support either none or both GFX_EDID ioctls,
> > > + * so the CAPS ioctl can also be used to probe for edid support.
> > > + *
> > > + * max_xres, max_yres - maximum display resolution supported.
> > > + *                      value "0" means no restriction.
> > > + *
> > > + */
> > > +struct vfio_device_gfx_edid_caps {
> > > +	__u32 argsz;
> > > +	__u32 flags;
> > > +	/* out */
> > > +	__u32 max_xres;
> > > +	__u32 max_yres;
> > > +};
Yeah, that's workable. And I also find  in qemu_edid_generate(), the generated
edid has display port  as the video input type. That's compatible with gvt-g
hard-coded edid.

So, do you plan to use VFIO_DEVICE_GFX_EDID_SET dynamically? To change
the display resolution during guest running? Could you elaborate more on
what the use case would be?

Besides, I think the proposed "VFIO_DEVICE_GFX_EDID_SET" can also provide
host a capability to trigger display monitor hot-plug event to guest, when host
wants to temporarily turn off vfio/display. Qemu can pass a special edid to
vendor driver to tell vendor driver to plug the guest display monitor out.

Thanks.

BR,
Tina
> 
> cheers,
>   Gerd