Re: [virtio-dev] Re: [PATCH v7] virtio-snd: add virtio sound device specification

[Gerd Hoffmann <kraxel@redhat.com>]

On Mon, Mar 16, 2020 at 09:30:59PM +0100, Anton Yakovlev wrote:
> Hi,
> 
> On 16.03.2020 11:19, Gerd Hoffmann wrote:
> >    Hi,
> > 
> > > 2. Rework jack configuration structure, now it's more aligned with the HDA spec.
> > 
> > Yep, that looks good.
> > 
> > > +\item[\field{hda_fn_nid}] indicates a functional node identifier
> > > +(see \hyperref[intro:HDA]{HDA}, section 7.1.2).
> > 
> > How is the nid used?
> 
> Since a functional group in HDA links entities of different kinds
> together, as an example, the linux driver can provide different groups
> as different PCM devices (and this well aligns with hardware case when
> streams with different capabilities live in different groups). This may
> be necessary to reassign the jack, because you need to know which
> streams are attached to the jacks. In addition, it will allow you to
> associate device controls with the stream/PCM device.

Ah, there is virtio_snd_pcm_config.hda_fn_nid.  So this is how jacks are
associated with streams.  Havn't noticed this update before.

> > In general some of the defconf and caps fields might need some
> > clarification if and how they are used, given we just cherry-pick
> > some items from the HDA spec ...
> 
> Yes, I also thought about it. But will this lead to a direct dependence
> on the HDA specification? If something changes there, we should update
> here. Therefore, I left these elements transparent and allowed the
> device/driver to decide on the wise use of these fields.

I'm mostly thinking about virtio-sound specific stuff which obviously
isn't covered by the HDA spec, like this:

> > If the "Presence Detect Capable" bit is set the status is available in
> > the "connected" field.

Most fields don't need a comment in virtio-sound, things like the jack
color should be pretty clear without that.

cheers,
  Gerd