Re: [virtio-dev] [RFC RESEND] virtio-video: Add virtio video device specification

Dmitry Sepp
2019-11-21T10:55:06Z

Hi Gerd,

On Mittwoch, 20. November 2019 12:29:29 CET Gerd Hoffmann wrote:
> Hi,
>
> > > > > 3. No support for getting plane requirements from the device (sg vs
> > > > > contig,
> > > > > size, stride alignment, plane count).
> > > >
> > > > There is actually a bigger difference that results in that. Vdec
> > > > assumes host-allocated buffers coming from a different device, e.g.
> > > > virtio-gpu and the host having the right knowledge to allocate the
> > > > buffers correctly. This is related to the fact that it's generally
> > > > difficult to convey all the allocation constraints in a generic
> > > > manner.
> > >
> > > Yep, buffer handling is tricky, especially when it comes to decoding
> > > directly to gpu buffers and also when supporting playback of
> > > drm-protected streams where the guest might not be allowed to access
> > > the stream data.
> >
> > Also, if we decide to have a buffer sharing device as Gerd suggested
> > in a different thread,
> > we'll get less overlaps between video codec feature and camera feature.
> > e.g. VIRTIO_VIDEO_T_RESOURCE_* would be simplified. (or removed?)
>
> Disclaimer: Havn't found the time yet to go over both virtio-video and
> virtio-vdec in detail.
>
> > As Tomasz said, I think virtio-vdec can be modified to support
> > encoding as well without big changes. I'm happy to update our
> > protocol and driver implementation to support encoding if needed.
>
> I think it makes sense to have a rough plan first ;)
> Is there a virtio-video implementation too?
Yes, of course. We will be ready to share the code very soon.

Regards,
Dmitry.

>
> When it comes to buffer handling: I don't like that virtio-vdec depends
> on virtio-gpu for buffer handling. Allowing sharing buffers between
> virtio-vdec and virtio-gpu (and possibly other devices) makes sense as
> an optional extension. But IMO the encoder/decoder device should be
> able to operate as stand-alone device.
>
> cheers,
> Gerd
>
>
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