Re: [virtio-dev] Re: [PATCH v5] virtio-snd: add virtio sound device specification

[Anton Yakovlev <anton.yakovlev@opensynergy.com>]

Hello all,

We have completed the implementation of the PoC specification v5. Below are 
our comments on what might or should be improved in the specification.

Initialization:

1. I think we should add the direction of the jack (in/out) to the
configuration of the jack. Because some properties (for example, a label for
some jack types) are based on this direction. The Linux HDA subsystem takes
this information from a pin/complex configuration. But we don't have (and
don't need) such entities.

2. The stream configuration contains âfeaturesâ that partially work as normal
virtio features, and partially do not. Maybe it is better to rename the field
to âflagsâ (as well as in the set_params request) and enter two sets of flags:
one is reported in the stream configuration, and the other is used in the
set_params request? This should make things less confusing.

Message-based PCM transport:

1. In the latest version of the specification, we resized the âfeaturesâ field
in the stream configuration (u8->le32), but forgot to do the same in the
set_params request. This should be fixed.

2. The device may report polling support for message-based transport. In this
case, the driver can be optimized so that it does not kick virtqueue for each
message.

3. For the input stream (capture), we decided to report the actual filled size
using the len field in the virtqueue descriptor. Should the specification
clearly indicate that the value contains sizeof(struct virtio_snd_pcm_status)
+ the size of the recorded frames?

4. We also need to add a device requirement to complete all pending messages
for a stream on a RELEASE request. Otherwise, they may become stuck in the
virtqueue.

We are looking forward for your comments.


--
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin