Re: [PATCH v2 4/9] ALSA: virtio: build PCM devices and substream hardware descriptors

[Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>]

On Sun, 24 Jan 2021, Anton Yakovlev wrote:

> Like the HDA specification, the virtio sound device specification links
> PCM substreams, jacks and PCM channel maps into functional groups. For
> each discovered group, a PCM device is created, the number of which
> coincides with the group number.
>
> Introduce the module parameters for setting the hardware buffer
> parameters:
>  pcm_buffer_ms [=160]
>  pcm_periods_min [=2]
>  pcm_periods_max [=16]
>  pcm_period_ms_min [=10]
>  pcm_period_ms_max [=80]
>
> Signed-off-by: Anton Yakovlev <anton.yakovlev@opensynergy.com>
> ---
> sound/virtio/Makefile      |   3 +-
> sound/virtio/virtio_card.c |  45 ++++
> sound/virtio/virtio_card.h |   9 +
> sound/virtio/virtio_pcm.c  | 536 +++++++++++++++++++++++++++++++++++++
> sound/virtio/virtio_pcm.h  |  89 ++++++
> 5 files changed, 681 insertions(+), 1 deletion(-)
> create mode 100644 sound/virtio/virtio_pcm.c
> create mode 100644 sound/virtio/virtio_pcm.h
>
> diff --git a/sound/virtio/Makefile b/sound/virtio/Makefile
> index dc551e637441..69162a545a41 100644
> --- a/sound/virtio/Makefile
> +++ b/sound/virtio/Makefile
> @@ -4,5 +4,6 @@ obj-$(CONFIG_SND_VIRTIO) += virtio_snd.o
>
> virtio_snd-objs := \
> 	virtio_card.o \
> -	virtio_ctl_msg.o
> +	virtio_ctl_msg.o \
> +	virtio_pcm.o
>
> diff --git a/sound/virtio/virtio_card.c b/sound/virtio/virtio_card.c
> index 955eadc2d858..39fe13b43dd1 100644
> --- a/sound/virtio/virtio_card.c
> +++ b/sound/virtio/virtio_card.c
> @@ -92,6 +92,17 @@ static void virtsnd_event_notify_cb(struct virtqueue *vqueue)
> 			if (!event)
> 				break;
>
> +			switch (le32_to_cpu(event->hdr.code)) {
> +			case VIRTIO_SND_EVT_PCM_PERIOD_ELAPSED:
> +			case VIRTIO_SND_EVT_PCM_XRUN: {

In the previous patch you had a switch-case statement complying to the 
common kernel coding style. It isn't specified in coding-style.rst, but 
these superfluous braces really don't seem to be good for anything - in 
this and multiple other switch-case statements in the series.

> +				virtsnd_pcm_event(snd, event);
> +				break;
> +			}
> +			default: {
> +				break;

An empty default doesn't seem very useful either. So the above could've 
just been

+			switch (le32_to_cpu(event->hdr.code)) {
+			case VIRTIO_SND_EVT_PCM_PERIOD_ELAPSED:
+			case VIRTIO_SND_EVT_PCM_XRUN:
+				virtsnd_pcm_event(snd, event);
+			}

> +			}
> +			}
> +
> 			virtsnd_event_send(queue->vqueue, event, true,
> 					   GFP_ATOMIC);
> 		}
> @@ -274,6 +285,16 @@ static int virtsnd_build_devs(struct virtio_snd *snd)
> 	strscpy(snd->card->longname, "VirtIO Sound Card",
> 		sizeof(snd->card->longname));
>
> +	rc = virtsnd_pcm_parse_cfg(snd);
> +	if (rc)
> +		return rc;
> +
> +	if (snd->nsubstreams) {
> +		rc = virtsnd_pcm_build_devs(snd);
> +		if (rc)
> +			return rc;
> +	}
> +
> 	return snd_card_register(snd->card);
> }
>
> @@ -302,6 +323,9 @@ static int virtsnd_validate(struct virtio_device *vdev)
> 		return -EINVAL;
> 	}
>
> +	if (virtsnd_pcm_validate(vdev))
> +		return -EINVAL;
> +
> 	return 0;
> }
>
> @@ -325,6 +349,7 @@ static int virtsnd_probe(struct virtio_device *vdev)
> 	snd->vdev = vdev;
> 	INIT_WORK(&snd->reset_work, virtsnd_reset_fn);
> 	INIT_LIST_HEAD(&snd->ctl_msgs);
> +	INIT_LIST_HEAD(&snd->pcm_list);
>
> 	vdev->priv = snd;
>
> @@ -359,6 +384,8 @@ static int virtsnd_probe(struct virtio_device *vdev)
> static void virtsnd_remove(struct virtio_device *vdev)
> {
> 	struct virtio_snd *snd = vdev->priv;
> +	struct virtio_pcm *pcm;
> +	struct virtio_pcm *pcm_next;
>
> 	if (!snd)
> 		return;
> @@ -376,6 +403,24 @@ static void virtsnd_remove(struct virtio_device *vdev)
> 	vdev->config->reset(vdev);
> 	vdev->config->del_vqs(vdev);
>
> +	list_for_each_entry_safe(pcm, pcm_next, &snd->pcm_list, list) {
> +		unsigned int i;
> +
> +		list_del(&pcm->list);
> +
> +		for (i = 0; i < ARRAY_SIZE(pcm->streams); ++i) {
> +			struct virtio_pcm_stream *stream = &pcm->streams[i];
> +
> +			if (stream->substreams)
> +				devm_kfree(&vdev->dev, stream->substreams);
> +		}
> +
> +		devm_kfree(&vdev->dev, pcm);

Please double-check both devm_kfree() calls above. Probably they aren't 
needed in the .remove() method.

> +	}
> +
> +	if (snd->substreams)
> +		devm_kfree(&vdev->dev, snd->substreams);
> +
> 	devm_kfree(&vdev->dev, snd);
>
> 	vdev->priv = NULL;
> diff --git a/sound/virtio/virtio_card.h b/sound/virtio/virtio_card.h
> index 37b734a92134..be6651a6aaf8 100644
> --- a/sound/virtio/virtio_card.h
> +++ b/sound/virtio/virtio_card.h
> @@ -24,6 +24,9 @@
> #include <uapi/linux/virtio_snd.h>
>
> #include "virtio_ctl_msg.h"
> +#include "virtio_pcm.h"
> +
> +struct virtio_pcm_substream;
>
> /**
>  * struct virtio_snd_queue - Virtqueue wrapper structure.
> @@ -43,6 +46,9 @@ struct virtio_snd_queue {
>  * @card: ALSA sound card.
>  * @ctl_msgs: Pending control request list.
>  * @event_msgs: Device events.
> + * @pcm_list: VirtIO PCM device list.
> + * @substreams: VirtIO PCM substreams.
> + * @nsubstreams: Number of PCM substreams.
>  */
> struct virtio_snd {
> 	struct virtio_device *vdev;
> @@ -51,6 +57,9 @@ struct virtio_snd {
> 	struct snd_card *card;
> 	struct list_head ctl_msgs;
> 	struct virtio_snd_event *event_msgs;
> +	struct list_head pcm_list;
> +	struct virtio_pcm_substream *substreams;
> +	unsigned int nsubstreams;
> };
>
> /* Message completion timeout in milliseconds (module parameter). */
> diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c
> new file mode 100644
> index 000000000000..036990b7b78a
> --- /dev/null
> +++ b/sound/virtio/virtio_pcm.c
> @@ -0,0 +1,536 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Sound card driver for virtio
> + * Copyright (C) 2020  OpenSynergy GmbH
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, see <http://www.gnu.org/licenses/>.
> + */
> +#include <linux/moduleparam.h>
> +#include <linux/virtio_config.h>
> +
> +#include "virtio_card.h"
> +
> +static unsigned int pcm_buffer_ms = 160;
> +module_param(pcm_buffer_ms, uint, 0644);
> +MODULE_PARM_DESC(pcm_buffer_ms, "PCM substream buffer time in milliseconds");
> +
> +static unsigned int pcm_periods_min = 2;
> +module_param(pcm_periods_min, uint, 0644);
> +MODULE_PARM_DESC(pcm_periods_min, "Minimum number of PCM periods");
> +
> +static unsigned int pcm_periods_max = 16;
> +module_param(pcm_periods_max, uint, 0644);
> +MODULE_PARM_DESC(pcm_periods_max, "Maximum number of PCM periods");
> +
> +static unsigned int pcm_period_ms_min = 10;
> +module_param(pcm_period_ms_min, uint, 0644);
> +MODULE_PARM_DESC(pcm_period_ms_min, "Minimum PCM period time in milliseconds");
> +
> +static unsigned int pcm_period_ms_max = 80;
> +module_param(pcm_period_ms_max, uint, 0644);
> +MODULE_PARM_DESC(pcm_period_ms_max, "Maximum PCM period time in milliseconds");
> +
> +/* Map for converting VirtIO format to ALSA format. */
> +static const unsigned int g_v2a_format_map[] = {
> +	[VIRTIO_SND_PCM_FMT_IMA_ADPCM] = SNDRV_PCM_FORMAT_IMA_ADPCM,
> +	[VIRTIO_SND_PCM_FMT_MU_LAW] = SNDRV_PCM_FORMAT_MU_LAW,
> +	[VIRTIO_SND_PCM_FMT_A_LAW] = SNDRV_PCM_FORMAT_A_LAW,
> +	[VIRTIO_SND_PCM_FMT_S8] = SNDRV_PCM_FORMAT_S8,
> +	[VIRTIO_SND_PCM_FMT_U8] = SNDRV_PCM_FORMAT_U8,
> +	[VIRTIO_SND_PCM_FMT_S16] = SNDRV_PCM_FORMAT_S16_LE,
> +	[VIRTIO_SND_PCM_FMT_U16] = SNDRV_PCM_FORMAT_U16_LE,
> +	[VIRTIO_SND_PCM_FMT_S18_3] = SNDRV_PCM_FORMAT_S18_3LE,
> +	[VIRTIO_SND_PCM_FMT_U18_3] = SNDRV_PCM_FORMAT_U18_3LE,
> +	[VIRTIO_SND_PCM_FMT_S20_3] = SNDRV_PCM_FORMAT_S20_3LE,
> +	[VIRTIO_SND_PCM_FMT_U20_3] = SNDRV_PCM_FORMAT_U20_3LE,
> +	[VIRTIO_SND_PCM_FMT_S24_3] = SNDRV_PCM_FORMAT_S24_3LE,
> +	[VIRTIO_SND_PCM_FMT_U24_3] = SNDRV_PCM_FORMAT_U24_3LE,
> +	[VIRTIO_SND_PCM_FMT_S20] = SNDRV_PCM_FORMAT_S20_LE,
> +	[VIRTIO_SND_PCM_FMT_U20] = SNDRV_PCM_FORMAT_U20_LE,
> +	[VIRTIO_SND_PCM_FMT_S24] = SNDRV_PCM_FORMAT_S24_LE,
> +	[VIRTIO_SND_PCM_FMT_U24] = SNDRV_PCM_FORMAT_U24_LE,
> +	[VIRTIO_SND_PCM_FMT_S32] = SNDRV_PCM_FORMAT_S32_LE,
> +	[VIRTIO_SND_PCM_FMT_U32] = SNDRV_PCM_FORMAT_U32_LE,
> +	[VIRTIO_SND_PCM_FMT_FLOAT] = SNDRV_PCM_FORMAT_FLOAT_LE,
> +	[VIRTIO_SND_PCM_FMT_FLOAT64] = SNDRV_PCM_FORMAT_FLOAT64_LE,
> +	[VIRTIO_SND_PCM_FMT_DSD_U8] = SNDRV_PCM_FORMAT_DSD_U8,
> +	[VIRTIO_SND_PCM_FMT_DSD_U16] = SNDRV_PCM_FORMAT_DSD_U16_LE,
> +	[VIRTIO_SND_PCM_FMT_DSD_U32] = SNDRV_PCM_FORMAT_DSD_U32_LE,
> +	[VIRTIO_SND_PCM_FMT_IEC958_SUBFRAME] =
> +		SNDRV_PCM_FORMAT_IEC958_SUBFRAME_LE
> +};
> +
> +/* Map for converting VirtIO frame rate to ALSA frame rate. */
> +struct virtsnd_v2a_rate {
> +	unsigned int alsa_bit;
> +	unsigned int rate;
> +};
> +
> +static const struct virtsnd_v2a_rate g_v2a_rate_map[] = {
> +	[VIRTIO_SND_PCM_RATE_5512] = { SNDRV_PCM_RATE_5512, 5512 },
> +	[VIRTIO_SND_PCM_RATE_8000] = { SNDRV_PCM_RATE_8000, 8000 },
> +	[VIRTIO_SND_PCM_RATE_11025] = { SNDRV_PCM_RATE_11025, 11025 },
> +	[VIRTIO_SND_PCM_RATE_16000] = { SNDRV_PCM_RATE_16000, 16000 },
> +	[VIRTIO_SND_PCM_RATE_22050] = { SNDRV_PCM_RATE_22050, 22050 },
> +	[VIRTIO_SND_PCM_RATE_32000] = { SNDRV_PCM_RATE_32000, 32000 },
> +	[VIRTIO_SND_PCM_RATE_44100] = { SNDRV_PCM_RATE_44100, 44100 },
> +	[VIRTIO_SND_PCM_RATE_48000] = { SNDRV_PCM_RATE_48000, 48000 },
> +	[VIRTIO_SND_PCM_RATE_64000] = { SNDRV_PCM_RATE_64000, 64000 },
> +	[VIRTIO_SND_PCM_RATE_88200] = { SNDRV_PCM_RATE_88200, 88200 },
> +	[VIRTIO_SND_PCM_RATE_96000] = { SNDRV_PCM_RATE_96000, 96000 },
> +	[VIRTIO_SND_PCM_RATE_176400] = { SNDRV_PCM_RATE_176400, 176400 },
> +	[VIRTIO_SND_PCM_RATE_192000] = { SNDRV_PCM_RATE_192000, 192000 }
> +};
> +
> +/**
> + * virtsnd_pcm_build_hw() - Parse substream config and build HW descriptor.
> + * @substream: VirtIO substream.
> + * @info: VirtIO substream information entry.
> + *
> + * Context: Any context.
> + * Return: 0 on success, -EINVAL if configuration is invalid.
> + */
> +static int virtsnd_pcm_build_hw(struct virtio_pcm_substream *substream,
> +				struct virtio_snd_pcm_info *info)
> +{
> +	struct virtio_device *vdev = substream->snd->vdev;
> +	unsigned int i;
> +	u64 values;
> +	size_t sample_max = 0;
> +	size_t sample_min = 0;
> +
> +	substream->features = le32_to_cpu(info->features);
> +
> +	/*
> +	 * TODO: set SNDRV_PCM_INFO_{BATCH,BLOCK_TRANSFER} if device supports
> +	 * only message-based transport.
> +	 */
> +	substream->hw.info =
> +		SNDRV_PCM_INFO_MMAP |
> +		SNDRV_PCM_INFO_MMAP_VALID |
> +		SNDRV_PCM_INFO_BATCH |
> +		SNDRV_PCM_INFO_BLOCK_TRANSFER |
> +		SNDRV_PCM_INFO_INTERLEAVED;
> +
> +	if (!info->channels_min || info->channels_min > info->channels_max) {
> +		dev_err(&vdev->dev,
> +			"SID %u: invalid channel range [%u %u]\n",
> +			substream->sid, info->channels_min, info->channels_max);
> +		return -EINVAL;
> +	}
> +
> +	substream->hw.channels_min = info->channels_min;
> +	substream->hw.channels_max = info->channels_max;
> +
> +	values = le64_to_cpu(info->formats);
> +
> +	substream->hw.formats = 0;
> +
> +	for (i = 0; i < ARRAY_SIZE(g_v2a_format_map); ++i)
> +		if (values & (1ULL << i)) {
> +			unsigned int alsa_fmt = g_v2a_format_map[i];
> +			int bytes = snd_pcm_format_physical_width(alsa_fmt) / 8;
> +
> +			if (!sample_min || sample_min > bytes)
> +				sample_min = bytes;
> +
> +			if (sample_max < bytes)
> +				sample_max = bytes;
> +
> +			substream->hw.formats |= (1ULL << alsa_fmt);
> +		}
> +
> +	if (!substream->hw.formats) {
> +		dev_err(&vdev->dev,
> +			"SID %u: no supported PCM sample formats found\n",
> +			substream->sid);
> +		return -EINVAL;
> +	}
> +
> +	values = le64_to_cpu(info->rates);
> +
> +	substream->hw.rates = 0;
> +
> +	for (i = 0; i < ARRAY_SIZE(g_v2a_rate_map); ++i)
> +		if (values & (1ULL << i)) {
> +			if (!substream->hw.rate_min ||
> +			    substream->hw.rate_min > g_v2a_rate_map[i].rate)
> +				substream->hw.rate_min = g_v2a_rate_map[i].rate;
> +
> +			if (substream->hw.rate_max < g_v2a_rate_map[i].rate)
> +				substream->hw.rate_max = g_v2a_rate_map[i].rate;
> +
> +			substream->hw.rates |= g_v2a_rate_map[i].alsa_bit;
> +		}
> +
> +	if (!substream->hw.rates) {
> +		dev_err(&vdev->dev,
> +			"SID %u: no supported PCM frame rates found\n",
> +			substream->sid);
> +		return -EINVAL;
> +	}
> +
> +	substream->hw.periods_min = pcm_periods_min;
> +	substream->hw.periods_max = pcm_periods_max;
> +
> +	/*
> +	 * We must ensure that there is enough space in the buffer to store
> +	 * pcm_buffer_ms ms for the combination (Cmax, Smax, Rmax), where:
> +	 *   Cmax = maximum supported number of channels,
> +	 *   Smax = maximum supported sample size in bytes,
> +	 *   Rmax = maximum supported frame rate.
> +	 */
> +	substream->hw.buffer_bytes_max =
> +		sample_max * substream->hw.channels_max * pcm_buffer_ms *
> +		(substream->hw.rate_max / MSEC_PER_SEC);
> +
> +	/* Align the buffer size to the page size */
> +	substream->hw.buffer_bytes_max =
> +		(substream->hw.buffer_bytes_max + PAGE_SIZE - 1) & -PAGE_SIZE;
> +
> +	/*
> +	 * We must ensure that the minimum period size is enough to store
> +	 * pcm_period_ms_min ms for the combination (Cmin, Smin, Rmin), where:
> +	 *   Cmin = minimum supported number of channels,
> +	 *   Smin = minimum supported sample size in bytes,
> +	 *   Rmin = minimum supported frame rate.
> +	 */
> +	substream->hw.period_bytes_min =
> +		sample_min * substream->hw.channels_min * pcm_period_ms_min *
> +		(substream->hw.rate_min / MSEC_PER_SEC);
> +
> +	/*
> +	 * We must ensure that the maximum period size is enough to store
> +	 * pcm_period_ms_max ms for the combination (Cmax, Smax, Rmax).
> +	 */
> +	substream->hw.period_bytes_max =
> +		sample_max * substream->hw.channels_max * pcm_period_ms_max *
> +		(substream->hw.rate_max / MSEC_PER_SEC);
> +
> +	return 0;
> +}
> +
> +/**
> + * virtsnd_pcm_prealloc_pages() - Preallocate substream hardware buffer.
> + * @substream: VirtIO substream.
> + *
> + * Context: Any context that permits to sleep.
> + * Return: 0 on success, -errno on failure.
> + */
> +static int virtsnd_pcm_prealloc_pages(struct virtio_pcm_substream *substream)
> +{
> +	struct snd_pcm_substream *ksubstream = substream->substream;
> +	size_t size = substream->hw.buffer_bytes_max;
> +	struct device *data = snd_dma_continuous_data(GFP_KERNEL);
> +
> +	/*
> +	 * We just allocate a CONTINUOUS buffer as it should work in any setup.
> +	 *
> +	 * If there is a need to use DEV(_XXX), then add this case here and
> +	 * (probably) update the related source code in other places.
> +	 */
> +	snd_pcm_lib_preallocate_pages(ksubstream, SNDRV_DMA_TYPE_CONTINUOUS,
> +				      data, size, size);
> +
> +	return 0;

looks like it can be void.

> +}
> +
> +/**
> + * virtsnd_pcm_find() - Find the PCM device for the specified node ID.
> + * @snd: VirtIO sound device.
> + * @nid: Function node ID.
> + *
> + * Context: Any context.
> + * Return: a pointer to the PCM device or ERR_PTR(-ENOENT).
> + */
> +struct virtio_pcm *virtsnd_pcm_find(struct virtio_snd *snd, unsigned int nid)
> +{
> +	struct virtio_pcm *pcm;
> +
> +	list_for_each_entry(pcm, &snd->pcm_list, list)
> +		if (pcm->nid == nid)
> +			return pcm;
> +
> +	return ERR_PTR(-ENOENT);
> +}
> +
> +/**
> + * virtsnd_pcm_find_or_create() - Find or create the PCM device for the
> + *                                specified node ID.
> + * @snd: VirtIO sound device.
> + * @nid: Function node ID.
> + *
> + * Context: Any context that permits to sleep.
> + * Return: a pointer to the PCM device or ERR_PTR(-errno).
> + */
> +struct virtio_pcm *virtsnd_pcm_find_or_create(struct virtio_snd *snd,
> +					      unsigned int nid)
> +{
> +	struct virtio_device *vdev = snd->vdev;
> +	struct virtio_pcm *pcm;
> +
> +	pcm = virtsnd_pcm_find(snd, nid);
> +	if (!IS_ERR(pcm))
> +		return pcm;
> +
> +	pcm = devm_kzalloc(&vdev->dev, sizeof(*pcm), GFP_KERNEL);
> +	if (!pcm)
> +		return ERR_PTR(-ENOMEM);
> +
> +	pcm->nid = nid;
> +	list_add_tail(&pcm->list, &snd->pcm_list);
> +
> +	return pcm;
> +}
> +
> +/**
> + * virtsnd_pcm_validate() - Validate if the device can be started.
> + * @vdev: VirtIO parent device.
> + *
> + * Context: Any context.
> + * Return: 0 on success, -EINVAL on failure.
> + */
> +int virtsnd_pcm_validate(struct virtio_device *vdev)
> +{
> +	if (pcm_periods_min < 2 || pcm_periods_min > pcm_periods_max) {
> +		dev_err(&vdev->dev,
> +			"invalid range [%u %u] of the number of PCM periods\n",
> +			pcm_periods_min, pcm_periods_max);
> +		return -EINVAL;
> +	}
> +
> +	if (!pcm_period_ms_min || pcm_period_ms_min > pcm_period_ms_max) {
> +		dev_err(&vdev->dev,
> +			"invalid range [%u %u] of the size of the PCM period\n",
> +			pcm_period_ms_min, pcm_period_ms_max);
> +		return -EINVAL;
> +	}
> +
> +	if (pcm_buffer_ms < pcm_periods_min * pcm_period_ms_min) {
> +		dev_err(&vdev->dev,
> +			"pcm_buffer_ms(=%u) value cannot be < %u ms\n",
> +			pcm_buffer_ms, pcm_periods_min * pcm_period_ms_min);
> +		return -EINVAL;
> +	}
> +
> +	if (pcm_period_ms_max > pcm_buffer_ms / 2) {
> +		dev_err(&vdev->dev,
> +			"pcm_period_ms_max(=%u) value cannot be > %u ms\n",
> +			pcm_period_ms_max, pcm_buffer_ms / 2);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * virtsnd_pcm_parse_cfg() - Parse the stream configuration.
> + * @snd: VirtIO sound device.
> + *
> + * This function is called during initial device initialization.
> + *
> + * Context: Any context that permits to sleep.
> + * Return: 0 on success, -errno on failure.
> + */
> +int virtsnd_pcm_parse_cfg(struct virtio_snd *snd)
> +{
> +	struct virtio_device *vdev = snd->vdev;
> +	struct virtio_snd_pcm_info *info;
> +	unsigned int i;
> +	int rc;
> +
> +	virtio_cread(vdev, struct virtio_snd_config, streams,
> +		     &snd->nsubstreams);
> +	if (!snd->nsubstreams)
> +		return 0;
> +
> +	snd->substreams = devm_kcalloc(&vdev->dev, snd->nsubstreams,
> +				       sizeof(*snd->substreams), GFP_KERNEL);
> +	if (!snd->substreams)
> +		return -ENOMEM;
> +
> +	info = devm_kcalloc(&vdev->dev, snd->nsubstreams, sizeof(*info),
> +			    GFP_KERNEL);

Just kmalloc() but make sure to free it in error cases below.

> +	if (!info)
> +		return -ENOMEM;
> +
> +	rc = virtsnd_ctl_query_info(snd, VIRTIO_SND_R_PCM_INFO, 0,
> +				    snd->nsubstreams, sizeof(*info), info);
> +	if (rc)
> +		return rc;
> +
> +	for (i = 0; i < snd->nsubstreams; ++i) {
> +		struct virtio_pcm_substream *substream = &snd->substreams[i];
> +		struct virtio_pcm *pcm;
> +
> +		substream->snd = snd;
> +		substream->sid = i;
> +
> +		rc = virtsnd_pcm_build_hw(substream, &info[i]);
> +		if (rc)
> +			return rc;
> +
> +		substream->nid = le32_to_cpu(info[i].hdr.hda_fn_nid);
> +
> +		pcm = virtsnd_pcm_find_or_create(snd, substream->nid);
> +		if (IS_ERR(pcm))
> +			return PTR_ERR(pcm);
> +
> +		switch (info[i].direction) {
> +		case VIRTIO_SND_D_OUTPUT: {

Same comment about braces and in other cases in the series.

> +			substream->direction = SNDRV_PCM_STREAM_PLAYBACK;
> +			break;
> +		}
> +		case VIRTIO_SND_D_INPUT: {
> +			substream->direction = SNDRV_PCM_STREAM_CAPTURE;
> +			break;
> +		}
> +		default: {
> +			dev_err(&vdev->dev, "SID %u: unknown direction (%u)\n",
> +				substream->sid, info[i].direction);
> +			return -EINVAL;
> +		}
> +		}
> +
> +		pcm->streams[substream->direction].nsubstreams++;
> +	}
> +
> +	devm_kfree(&vdev->dev, info);
> +
> +	return 0;
> +}
> +
> +/**
> + * virtsnd_pcm_build_devs() - Build ALSA PCM devices.
> + * @snd: VirtIO sound device.
> + *
> + * Context: Any context that permits to sleep.
> + * Return: 0 on success, -errno on failure.
> + */
> +int virtsnd_pcm_build_devs(struct virtio_snd *snd)
> +{
> +	struct virtio_device *vdev = snd->vdev;
> +	struct virtio_pcm *pcm;
> +	unsigned int i;
> +	int rc;
> +
> +	list_for_each_entry(pcm, &snd->pcm_list, list) {
> +		unsigned int npbs =
> +			pcm->streams[SNDRV_PCM_STREAM_PLAYBACK].nsubstreams;
> +		unsigned int ncps =
> +			pcm->streams[SNDRV_PCM_STREAM_CAPTURE].nsubstreams;
> +
> +		if (!npbs && !ncps)
> +			continue;
> +
> +		rc = snd_pcm_new(snd->card, "virtio_snd", pcm->nid, npbs, ncps,
> +				 &pcm->pcm);
> +		if (rc) {
> +			dev_err(&vdev->dev, "snd_pcm_new[%u] failed: %d\n",
> +				pcm->nid, rc);
> +			return rc;
> +		}
> +
> +		pcm->pcm->info_flags = 0;
> +		pcm->pcm->dev_class = SNDRV_PCM_CLASS_GENERIC;
> +		pcm->pcm->dev_subclass = SNDRV_PCM_SUBCLASS_GENERIC_MIX;
> +		strscpy(pcm->pcm->name, "VirtIO PCM", sizeof(pcm->pcm->name));
> +
> +		pcm->pcm->private_data = pcm;
> +
> +		for (i = 0; i < ARRAY_SIZE(pcm->streams); ++i) {
> +			struct virtio_pcm_stream *stream = &pcm->streams[i];
> +
> +			if (!stream->nsubstreams)
> +				continue;
> +
> +			stream->substreams =
> +				devm_kcalloc(&vdev->dev,
> +					     stream->nsubstreams,
> +					     sizeof(*stream->substreams),
> +					     GFP_KERNEL);
> +			if (!stream->substreams)
> +				return -ENOMEM;
> +
> +			stream->nsubstreams = 0;
> +		}
> +	}
> +
> +	for (i = 0; i < snd->nsubstreams; ++i) {
> +		struct virtio_pcm_substream *substream = &snd->substreams[i];
> +		struct virtio_pcm_stream *stream;
> +
> +		pcm = virtsnd_pcm_find(snd, substream->nid);
> +		if (IS_ERR(pcm))
> +			return PTR_ERR(pcm);
> +
> +		stream = &pcm->streams[substream->direction];
> +		stream->substreams[stream->nsubstreams++] = substream;
> +	}
> +
> +	list_for_each_entry(pcm, &snd->pcm_list, list)
> +		for (i = 0; i < ARRAY_SIZE(pcm->streams); ++i) {
> +			struct virtio_pcm_stream *stream = &pcm->streams[i];
> +			struct snd_pcm_str *kstream;
> +			struct snd_pcm_substream *ksubstream;
> +
> +			if (!stream->nsubstreams)
> +				continue;
> +
> +			kstream = &pcm->pcm->streams[i];
> +			ksubstream = kstream->substream;
> +
> +			while (ksubstream) {

cosmetic: this could be

 	for (substream = kstream->substream; ksubstream; ksubstream = ksubstream->next)

> +				struct virtio_pcm_substream *substream =
> +					stream->substreams[ksubstream->number];
> +
> +				substream->substream = ksubstream;
> +				ksubstream = ksubstream->next;
> +
> +				rc = virtsnd_pcm_prealloc_pages(substream);
> +				if (rc)
> +					return rc;
> +			}
> +		}
> +
> +	return 0;
> +}
> +
> +/**
> + * virtsnd_pcm_event() - Handle the PCM device event notification.
> + * @snd: VirtIO sound device.
> + * @event: VirtIO sound event.
> + *
> + * Context: Interrupt context.
> + */
> +void virtsnd_pcm_event(struct virtio_snd *snd, struct virtio_snd_event *event)
> +{
> +	struct virtio_pcm_substream *substream;
> +	unsigned int sid = le32_to_cpu(event->data);
> +
> +	if (sid >= snd->nsubstreams)
> +		return;
> +
> +	substream = &snd->substreams[sid];
> +
> +	switch (le32_to_cpu(event->hdr.code)) {
> +	case VIRTIO_SND_EVT_PCM_PERIOD_ELAPSED: {
> +		/* TODO: deal with shmem elapsed period */
> +		break;
> +	}
> +	case VIRTIO_SND_EVT_PCM_XRUN: {
> +		break;
> +	}
> +	}
> +}

Thanks
Guennadi