Re: [virtio-dev] virtio-snd comments/questions

Radu Ocica
2023-11-09T16:46:50Z

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> Could you elaborate on this? Which audio backend would not support
> PAUSE? I am not very familiar with audio engines.

For instance in linux, alsa-lib has a flag that specifies pause support by a PCM stream:
#define SNDRV_PCM_INFO_PAUSE (1UL<<19) /* pause ioctl is supported */
The snd_pcm_pause API can only be used successfully if the PCM stream has this bit set in its PCM info.
A similar concept exists in QNX sound.

>> This looks promising. I found it already at https://urldefense.com/v3/__https://github.com/torvalds/linux/blob/master/sound/virtio/__;!!JoeW-IhCUkS0Jg!bBq1USPrJoN1_CBJkW-XBknkCSEOUP40V1ctr_OU0tsYyEr9pXjSEu7n5ibc5BL4fKT3Utk-cpGw6FiWxDY$ and will give it a try. Is there a repository for this driver code where both this fix and the audio control support is available?
>>
>>

> What do you mean with audio control support? Are you talking about the
> device? The device implementation is at
https://urldefense.com/v3/__https://github.com/rust-vmm/vhost-device/tree/main/staging__;!!JoeW-IhCUkS0Jg!bBq1USPrJoN1_CBJkW-XBknkCSEOUP40V1ctr_OU0tsYyEr9pXjSEu7n5ibc5BL4fKT3Utk-cpGw1sNq6IY$ .

I meant the support for feature VIRTIO_SND_F_CTLS in the virtio_snd guest driver. A patch to add this support is available here: https://lists.oasis-open.org/archives/virtio-comment/202104/msg00013.html. However this patch is not present in the virtio_snd guest driver version here: https://urldefense.com/v3/__https://github.com/torvalds/linux/blob/master/sound/virtio/__;!!JoeW-IhCUkS0Jg!bBq1USPrJoN1_CBJkW-XBknkCSEOUP40V1ctr_OU0tsYyEr9pXjSEu7n5ibc5BL4fKT3Utk-cpGw6FiWxDY$ . I was wondering whether there is a repository where the virtio_snd driver has both the VIRTIO_SND_F_CTLS support and the ack callback patch.

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