Re: [virtio-comment] [PATCH] virtio-snd: add support for audio controls

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Jul 27, 2021 at 05:57:23PM +0200, Cornelia Huck wrote:
> On Tue, Apr 20 2021, Anton Yakovlev <anton.yakovlev@opensynergy.com> wrote:
> 
> > This patch extends the virtio sound device specification by adding
> > support for audio controls. Audio controls can be used to set the volume
> > level, mute/unmute the audio signal, switch different modes/states of
> > the virtual sound device, etc.
> >
> > Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
> > ---
> >  conformance.tex  |   5 +
> >  virtio-sound.tex | 374 ++++++++++++++++++++++++++++++++++++++++++++++-
> >  2 files changed, 378 insertions(+), 1 deletion(-)
> >
> 
> > @@ -50,6 +53,7 @@ \subsection{Device Configuration Layout}\label{sec:Device Types / Sound Device /
> >      le32 jacks;
> >      le32 streams;
> >      le32 chmaps;
> > +    le32 controls;
> >  };
> >  \end{lstlisting}
> >  
> > @@ -62,6 +66,9 @@ \subsection{Device Configuration Layout}\label{sec:Device Types / Sound Device /
> >  PCM streams.
> >  \item[\field{chmaps}] (driver-read-only) indicates a total number of all available
> >  channel maps.
> > +\item[\field{controls}] (driver-read-only) indicates a total number of all available
> > +control elements if VIRTIO_SND_F_CTLS has been negotiated.
> 
> While the driver is not supposed to read this if the feature has not
> been negotiated, do we also want to add a normative statement about what
> the device is supposed to do in this case? Does the field always exist?


Cornelia this is a general issue in the spec. We should be clearer
that
- drivers should be ready for config space to be shorter
or longer than described here, as long as they do not
need to access outside of it, it is ok.
- negotiated/offered confusion


I will revive my proposal where feature is negotiated even before
FEATURES_OK

I think this can stand as is for now.

-- 
MST