[PATCH v9 12/12] docs/system: add basic virtio-snd documentation

[Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>]

This commit adds basic documentation for using virtio-snd.

Signed-off-by: Emmanouil Pitsidianakis <manos.pitsidianakis@linaro.org>
---
 docs/system/device-emulation.rst   |  1 +
 docs/system/devices/virtio-snd.rst | 49 ++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 docs/system/devices/virtio-snd.rst

diff --git a/docs/system/device-emulation.rst b/docs/system/device-emulation.rst
index 4491c4cbf7..dae19446e5 100644
--- a/docs/system/device-emulation.rst
+++ b/docs/system/device-emulation.rst
@@ -92,6 +92,7 @@ Emulated Devices
    devices/usb.rst
    devices/vhost-user.rst
    devices/virtio-pmem.rst
+   devices/virtio-snd.rst
    devices/vhost-user-rng.rst
    devices/canokey.rst
    devices/usb-u2f.rst
diff --git a/docs/system/devices/virtio-snd.rst b/docs/system/devices/virtio-snd.rst
new file mode 100644
index 0000000000..2a9187fd70
--- /dev/null
+++ b/docs/system/devices/virtio-snd.rst
@@ -0,0 +1,49 @@
+virtio sound
+============
+
+This document explains the setup and usage of the Virtio sound device.
+The Virtio sound device is a paravirtualized sound card device.
+
+Linux kernel support
+--------------------
+
+Virtio sound requires a guest Linux kernel built with the
+``CONFIG_SND_VIRTIO`` option.
+
+Description
+-----------
+
+Virtio sound implements capture and playback from inside a guest using the
+configured audio backend of the host machine.
+
+Device properties
+-----------------
+
+The Virtio sound device can be configured with the following properties:
+
+ * ``jacks`` number of physical jacks (Unimplemented).
+ * ``streams`` number of PCM streams. At the moment, no stream configuration is supported: the first one will always be a playback stream, an optional second will always be a capture stream. Adding more will cycle stream directions from playback to capture.
+ * ``chmaps`` number of channel maps (Unimplemented).
+
+All streams are stereo and have the default channel positions ``Front left, right``.
+
+Examples
+--------
+
+Add an audio device and an audio backend at once with ``-audio`` and ``model=virtio``:
+
+ * pulseaudio: ``-audio driver=pa,model=virtio``
+   or ``-audio driver=pa,model=virtio,server=/run/user/1000/pulse/native``
+ * sdl: ``-audio driver=sdl,model=virtio``
+ * coreaudio: ``-audio driver=coreaudio,model=virtio``
+
+etc.
+
+To specifically add virtualized sound devices, you have to specify a PCI device
+and an audio backend listed with ``-audio driver=help`` that works on your host
+machine, e.g.:
+
+::
+
+  -device virtio-sound-pci,audiodev=my_audiodev \
+  -audiodev alsa,id=my_audiodev
-- 
2.39.2