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Re: [libvirt] [PATCH] qemu: sound: Support intel 'hda' model



On Tue, Jan 11, 2011 at 11:46:14AM +0100, Gerd Hoffmann wrote:
> On 01/10/11 18:19, Cole Robinson wrote:
> >In QEMU, the card itself is a PCI device, but it requires
> >-device hda-output in order to actually get sound to the host. AIUI this
> >is just HDA configuration and does not require stable addressing, so
> >is not presently represented in the XML.
> 
> It isn't that simple.  There are actually multiple devices involved.
> Each audio codec (yes, there can be multiple of these, up to 15) is
> connected via HDA Link to the pci controller.  Each audio codec has
> a codec address (HDA bus property: cad=[0..14]).
>
> So you can specify "-device intel-hda -device hda-duplex -device
> hda-output" and the guest has multiple audio devices.  Win7 even
> handles this correctly, whereas alsa uses only the first codec it
> finds (lowest codec address).  Not that this buys you much today,
> qemu mixes all channels together before sending them off to the
> hosts sound system, i.e. you don't see a stream per sound card in
> pulseaudio.  That might change in the future though.
> 

So 'intel-hda' should really be considered as a controller,
and hda-output' & 'hda-duplex' are the things to be treated
as devices in the guest config.

This suggests a setup more like the one we did for virtio-serial
where we'd invent a new address type for codecs, and have XML
looking something like

    <controller type='hda' model='ich6'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/>
    </controller>
    <sound model='hda-output'>
      <address type='hda' codec='0'/>
    </sound>
    <sound model='hda-duplex'>
      <address type='hda' codec='1'/>
    </sound>

Are there any technical model names for 'hda-output' 'hda-duplex'
we need to be aware of (as we potentially have ich6, ich7, 8, 9,
etc for intel-hda in the future)

> We also might see more hda codecs in the future.  Maybe to pass
> through digital audio interfaces from the host?  Not investigated
> yet in detail though.
> 
> The HDA Links are even hot-pluggable (new audio codec can be linked
> up when putting the laptop into the docking station for example),
> although the qemu emulation doesn't support that today.

Hotplug is another good reason for us to treat the 'hda-output'
and 'hda-duplex' objects as the <sound> device in libvirt XML,
because then we can add/remove them via virDomainAttachDevice
which we couldn't otherwise do

Regards,
Daniel


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