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

[Dmitry Sepp <dmitry.sepp@opensynergy.com>]

Hi,

On Dienstag, 17. Dezember 2019 15:09:16 CET Keiichi Watanabe wrote:
> Hi,
> 
> Thanks Tomasz and Gerd for the suggestions and information.
> 
> On Tue, Dec 17, 2019 at 10:39 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
> >   Hi,
> >   
> > > On the host side, the encode and decode APIs are different as well, so
> > > having separate implementation decoder and encoder, possibly just
> > > sharing some helper code, would make much more sense.
> > 
> > When going down that route I'd suggest to use two device ids (even when
> > specifying both variants in one spec section and one header file due to
> > the overlaps) instead of feature flags.
> 
> Sounds good. It makes sense to use different device IDs for different
> devices.
Does this mean one driver handles both? Or we have two separate drivers?

> > > > I don't think using fourcc is a problem, and given that both drm and
> > > > v4l2 use fourcc already this would be a good choice I think.
> > > 
> > > Both DRM and V4L2 use two mutually incompatible sets of FourCCs, so
> > > I'm not sure how it could be a good choice. At least unless we decide
> > > to pick a specific set of FourCC. It doesn't help that Windows/DirectX
> > > has its own set of FourCCs that's again slightly different than the
> > > two mentioned before.
> > 
> > Ouch, wasn't aware of that.  That makes reusing fourcc codes much less
> > useful.
> > 
> > > > But the definition should be more specific than just "fourcc".  Best
> > > > would be to explicitly list and define each format supported by the
> > > > spec.
> > > 
> > > Why not be consistent with virtio-gpu and just define new formats as
> > > we add support for them as sequential integers?
> > 
> > Yes, lets do that.
> 
> It makes sense. I seems to have overestimated FourCC.
This is what was actually done in the driver code already (it is a bit ahead 
of the spec, but I guess no one has looked at it so far).

Regards,
Dmitry.

> 
> Best,
> Keiichi
> 
> > cheers,
> > 
> >   Gerd