On Tue, Jan 11, 2011 at 11:10:04AM +0000, Daniel P. Berrange wrote:
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
One further alternative is to explicitly list codecs under the <sound> element eg <sound model='ich6'> <codec name='output' slot=0/> <codec name='duplex' slot=3/> <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' function='0x0'/> </sound> We could use virDomainAttachDevice/DetachDevice to hotplug an entire ich6 device, and virDomainUpdateDevice to hotplug individual codecs within the device. This might be a slightly nicer option for applications, so it would more closely mesh with what the guest OS actually sees as its device(s). Daniel