Re: [PATCH 1/2] vfio: add edid api for display (vgpu) devices.

Zhenyu Wang
2018-09-17T09:15:50Z

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On 2018.09.17 10:50:33 +0200, Gerd Hoffmann wrote:
> > > +#define VFIO_DEVICE_INFO_CAP_EDID 1
> > > +
> > > +struct vfio_device_info_edid_cap {
> > > + struct vfio_info_cap_header header;
> > > + __u32 max_x; /* Max display height (zero == no limit) */
> > > + __u32 max_y; /* Max display height (zero == no limit) */
> > > +};
> >
> > As current virtual display for Intel vGPU is still emulating against real HW
> > pipeline with same limitations, asked display developers that whether or not
> > specific mode can work might still depend on current or future HW behavior.
> > So could we add some hints on what kind of edid mode vfio device can operate?
> > Some may support arbitrary modes, but some may only support standard modes.
>
> What kind of restrictions do we have here? Really to a fixed list of
> standard modes?

Restriction is still with HW differences, e.g for skl/kbl with ddi wrpll
within min/max clock range which may generate any required frequency, but
I've been told for bxt there're some gaps in clock range that could be
generated.

>
> Some testing (kaby lake) indicates y axis has no restrictions and x axis
> gets rounded up to the next multiple of 8 pixels (32 bytes), maybe to
> align scanlines with cachelines?

That should be plane stride requirement I think.

>
> Oh, and btw: Seems the resolution restriction (to 1024x768 for the
> smallest vgpu type) seems to not be enforced. Intentional?
>

hmm, what do you mean here? Not enforce to have only one mode for vgpu type?
Or can't change to other mode?

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