ALSA: virtio: build PCM devices and substream hardware descriptors

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>
Link: https://lore.kernel.org/r/20210302164709.3142702-5-anton.yakovlev@opensynergy.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

5 files changed, 581 insertions, 1 deletions

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 b757b2444078..11c76ee311b7 100644
--- a/sound/virtio/virtio_card.c
+++ b/sound/virtio/virtio_card.c
@@ -209,6 +209,16 @@ static int virtsnd_build_devs(struct virtio_snd *snd)
 			 VIRTIO_SND_CARD_NAME " at %s/%s",
 			 dev_name(dev->parent), dev_name(dev));
 
+	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);
 }
 
@@ -237,6 +247,9 @@ static int virtsnd_validate(struct virtio_device *vdev)
 		return -EINVAL;
 	}
 
+	if (virtsnd_pcm_validate(vdev))
+		return -EINVAL;
+
 	return 0;
 }
 
@@ -259,6 +272,7 @@ static int virtsnd_probe(struct virtio_device *vdev)
 
 	snd->vdev = vdev;
 	INIT_LIST_HEAD(&snd->ctl_msgs);
+	INIT_LIST_HEAD(&snd->pcm_list);
 
 	vdev->priv = snd;
 
@@ -293,6 +307,7 @@ on_exit:
 static void virtsnd_remove(struct virtio_device *vdev)
 {
 	struct virtio_snd *snd = vdev->priv;
+	unsigned int i;
 
 	virtsnd_disable_event_vq(snd);
 	virtsnd_ctl_msg_cancel_all(snd);
@@ -303,6 +318,9 @@ static void virtsnd_remove(struct virtio_device *vdev)
 	vdev->config->del_vqs(vdev);
 	vdev->config->reset(vdev);
 
+	for (i = 0; snd->substreams && i < snd->nsubstreams; ++i)
+		cancel_work_sync(&snd->substreams[i].elapsed_period);
+
 	kfree(snd->event_msgs);
 }
 
diff --git a/sound/virtio/virtio_card.h b/sound/virtio/virtio_card.h
index 1e76eeff160f..77a1b7255370 100644
--- a/sound/virtio/virtio_card.h
+++ b/sound/virtio/virtio_card.h
@@ -12,9 +12,13 @@
 #include <uapi/linux/virtio_snd.h>
 
 #include "virtio_ctl_msg.h"
+#include "virtio_pcm.h"
 
 #define VIRTIO_SND_CARD_DRIVER	"virtio-snd"
 #define VIRTIO_SND_CARD_NAME	"VirtIO SoundCard"
+#define VIRTIO_SND_PCM_NAME	"VirtIO PCM"
+
+struct virtio_pcm_substream;
 
 /**
  * struct virtio_snd_queue - Virtqueue wrapper structure.
@@ -33,6 +37,9 @@ 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;
@@ -40,6 +47,9 @@ 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;
+	u32 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..e16567e2e214
--- /dev/null
+++ b/sound/virtio/virtio_pcm.c
@@ -0,0 +1,479 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * virtio-snd: Virtio sound device
+ * Copyright (C) 2021 OpenSynergy GmbH
+ */
+#include <linux/moduleparam.h>
+#include <linux/virtio_config.h>
+
+#include "virtio_card.h"
+
+static u32 pcm_buffer_ms = 160;
+module_param(pcm_buffer_ms, uint, 0644);
+MODULE_PARM_DESC(pcm_buffer_ms, "PCM substream buffer time in milliseconds");
+
+static u32 pcm_periods_min = 2;
+module_param(pcm_periods_min, uint, 0644);
+MODULE_PARM_DESC(pcm_periods_min, "Minimum number of PCM periods");
+
+static u32 pcm_periods_max = 16;
+module_param(pcm_periods_max, uint, 0644);
+MODULE_PARM_DESC(pcm_periods_max, "Maximum number of PCM periods");
+
+static u32 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 u32 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 snd_pcm_format_t 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.
+ * @vss: 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 *vss,
+				struct virtio_snd_pcm_info *info)
+{
+	struct virtio_device *vdev = vss->snd->vdev;
+	unsigned int i;
+	u64 values;
+	size_t sample_max = 0;
+	size_t sample_min = 0;
+
+	vss->features = le32_to_cpu(info->features);
+
+	/*
+	 * TODO: set SNDRV_PCM_INFO_{BATCH,BLOCK_TRANSFER} if device supports
+	 * only message-based transport.
+	 */
+	vss->hw.info =
+		SNDRV_PCM_INFO_MMAP |
+		SNDRV_PCM_INFO_MMAP_VALID |
+		SNDRV_PCM_INFO_BATCH |
+		SNDRV_PCM_INFO_BLOCK_TRANSFER |
+		SNDRV_PCM_INFO_INTERLEAVED |
+		SNDRV_PCM_INFO_PAUSE;
+
+	if (!info->channels_min || info->channels_min > info->channels_max) {
+		dev_err(&vdev->dev,
+			"SID %u: invalid channel range [%u %u]\n",
+			vss->sid, info->channels_min, info->channels_max);
+		return -EINVAL;
+	}
+
+	vss->hw.channels_min = info->channels_min;
+	vss->hw.channels_max = info->channels_max;
+
+	values = le64_to_cpu(info->formats);
+
+	vss->hw.formats = 0;
+
+	for (i = 0; i < ARRAY_SIZE(g_v2a_format_map); ++i)
+		if (values & (1ULL << i)) {
+			snd_pcm_format_t 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;
+
+			vss->hw.formats |= pcm_format_to_bits(alsa_fmt);
+		}
+
+	if (!vss->hw.formats) {
+		dev_err(&vdev->dev,
+			"SID %u: no supported PCM sample formats found\n",
+			vss->sid);
+		return -EINVAL;
+	}
+
+	values = le64_to_cpu(info->rates);
+
+	vss->hw.rates = 0;
+
+	for (i = 0; i < ARRAY_SIZE(g_v2a_rate_map); ++i)
+		if (values & (1ULL << i)) {
+			if (!vss->hw.rate_min ||
+			    vss->hw.rate_min > g_v2a_rate_map[i].rate)
+				vss->hw.rate_min = g_v2a_rate_map[i].rate;
+
+			if (vss->hw.rate_max < g_v2a_rate_map[i].rate)
+				vss->hw.rate_max = g_v2a_rate_map[i].rate;
+
+			vss->hw.rates |= g_v2a_rate_map[i].alsa_bit;
+		}
+
+	if (!vss->hw.rates) {
+		dev_err(&vdev->dev,
+			"SID %u: no supported PCM frame rates found\n",
+			vss->sid);
+		return -EINVAL;
+	}
+
+	vss->hw.periods_min = pcm_periods_min;
+	vss->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.
+	 */
+	vss->hw.buffer_bytes_max =
+		PAGE_ALIGN(sample_max * vss->hw.channels_max * pcm_buffer_ms *
+			   (vss->hw.rate_max / MSEC_PER_SEC));
+
+	/*
+	 * 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.
+	 */
+	vss->hw.period_bytes_min =
+		sample_min * vss->hw.channels_min * pcm_period_ms_min *
+		(vss->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).
+	 */
+	vss->hw.period_bytes_max =
+		sample_max * vss->hw.channels_max * pcm_period_ms_max *
+		(vss->hw.rate_max / MSEC_PER_SEC);
+
+	return 0;
+}
+
+/**
+ * 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, u32 nid)
+{
+	struct virtio_pcm *vpcm;
+
+	list_for_each_entry(vpcm, &snd->pcm_list, list)
+		if (vpcm->nid == nid)
+			return vpcm;
+
+	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, u32 nid)
+{
+	struct virtio_device *vdev = snd->vdev;
+	struct virtio_pcm *vpcm;
+
+	vpcm = virtsnd_pcm_find(snd, nid);
+	if (!IS_ERR(vpcm))
+		return vpcm;
+
+	vpcm = devm_kzalloc(&vdev->dev, sizeof(*vpcm), GFP_KERNEL);
+	if (!vpcm)
+		return ERR_PTR(-ENOMEM);
+
+	vpcm->nid = nid;
+	list_add_tail(&vpcm->list, &snd->pcm_list);
+
+	return vpcm;
+}
+
+/**
+ * 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_period_elapsed() - Kernel work function to handle the elapsed
+ *                                period state.
+ * @work: Elapsed period work.
+ *
+ * The main purpose of this function is to call snd_pcm_period_elapsed() in
+ * a process context, not in an interrupt context. This is necessary because PCM
+ * devices operate in non-atomic mode.
+ *
+ * Context: Process context.
+ */
+static void virtsnd_pcm_period_elapsed(struct work_struct *work)
+{
+	struct virtio_pcm_substream *vss =
+		container_of(work, struct virtio_pcm_substream, elapsed_period);
+
+	snd_pcm_period_elapsed(vss->substream);
+}
+
+/**
+ * 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;
+	u32 i;
+	int rc;
+
+	virtio_cread_le(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 = kcalloc(snd->nsubstreams, sizeof(*info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	rc = virtsnd_ctl_query_info(snd, VIRTIO_SND_R_PCM_INFO, 0,
+				    snd->nsubstreams, sizeof(*info), info);
+	if (rc)
+		goto on_exit;
+
+	for (i = 0; i < snd->nsubstreams; ++i) {
+		struct virtio_pcm_substream *vss = &snd->substreams[i];
+		struct virtio_pcm *vpcm;
+
+		vss->snd = snd;
+		vss->sid = i;
+		INIT_WORK(&vss->elapsed_period, virtsnd_pcm_period_elapsed);
+
+		rc = virtsnd_pcm_build_hw(vss, &info[i]);
+		if (rc)
+			goto on_exit;
+
+		vss->nid = le32_to_cpu(info[i].hdr.hda_fn_nid);
+
+		vpcm = virtsnd_pcm_find_or_create(snd, vss->nid);
+		if (IS_ERR(vpcm)) {
+			rc = PTR_ERR(vpcm);
+			goto on_exit;
+		}
+
+		switch (info[i].direction) {
+		case VIRTIO_SND_D_OUTPUT:
+			vss->direction = SNDRV_PCM_STREAM_PLAYBACK;
+			break;
+		case VIRTIO_SND_D_INPUT:
+			vss->direction = SNDRV_PCM_STREAM_CAPTURE;
+			break;
+		default:
+			dev_err(&vdev->dev, "SID %u: unknown direction (%u)\n",
+				vss->sid, info[i].direction);
+			rc = -EINVAL;
+			goto on_exit;
+		}
+
+		vpcm->streams[vss->direction].nsubstreams++;
+	}
+
+on_exit:
+	kfree(info);
+
+	return rc;
+}
+
+/**
+ * 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 *vpcm;
+	u32 i;
+	int rc;
+
+	list_for_each_entry(vpcm, &snd->pcm_list, list) {
+		unsigned int npbs =
+			vpcm->streams[SNDRV_PCM_STREAM_PLAYBACK].nsubstreams;
+		unsigned int ncps =
+			vpcm->streams[SNDRV_PCM_STREAM_CAPTURE].nsubstreams;
+
+		if (!npbs && !ncps)
+			continue;
+
+		rc = snd_pcm_new(snd->card, VIRTIO_SND_CARD_DRIVER, vpcm->nid,
+				 npbs, ncps, &vpcm->pcm);
+		if (rc) {
+			dev_err(&vdev->dev, "snd_pcm_new[%u] failed: %d\n",
+				vpcm->nid, rc);
+			return rc;
+		}
+
+		vpcm->pcm->info_flags = 0;
+		vpcm->pcm->dev_class = SNDRV_PCM_CLASS_GENERIC;
+		vpcm->pcm->dev_subclass = SNDRV_PCM_SUBCLASS_GENERIC_MIX;
+		snprintf(vpcm->pcm->name, sizeof(vpcm->pcm->name),
+			 VIRTIO_SND_PCM_NAME " %u", vpcm->pcm->device);
+		vpcm->pcm->private_data = vpcm;
+		vpcm->pcm->nonatomic = true;
+
+		for (i = 0; i < ARRAY_SIZE(vpcm->streams); ++i) {
+			struct virtio_pcm_stream *stream = &vpcm->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_stream *vs;
+		struct virtio_pcm_substream *vss = &snd->substreams[i];
+
+		vpcm = virtsnd_pcm_find(snd, vss->nid);
+		if (IS_ERR(vpcm))
+			return PTR_ERR(vpcm);
+
+		vs = &vpcm->streams[vss->direction];
+		vs->substreams[vs->nsubstreams++] = vss;
+	}
+
+	list_for_each_entry(vpcm, &snd->pcm_list, list) {
+		for (i = 0; i < ARRAY_SIZE(vpcm->streams); ++i) {
+			struct virtio_pcm_stream *vs = &vpcm->streams[i];
+			struct snd_pcm_str *ks = &vpcm->pcm->streams[i];
+			struct snd_pcm_substream *kss;
+
+			if (!vs->nsubstreams)
+				continue;
+
+			for (kss = ks->substream; kss; kss = kss->next)
+				vs->substreams[kss->number]->substream = kss;
+		}
+
+		snd_pcm_set_managed_buffer_all(vpcm->pcm,
+					       SNDRV_DMA_TYPE_VMALLOC, NULL,
+					       0, 0);
+	}
+
+	return 0;
+}
diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h
new file mode 100644
index 000000000000..84f2f3f14f48
--- /dev/null
+++ b/sound/virtio/virtio_pcm.h
@@ -0,0 +1,72 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * virtio-snd: Virtio sound device
+ * Copyright (C) 2021 OpenSynergy GmbH
+ */
+#ifndef VIRTIO_SND_PCM_H
+#define VIRTIO_SND_PCM_H
+
+#include <linux/atomic.h>
+#include <linux/virtio_config.h>
+#include <sound/pcm.h>
+
+struct virtio_pcm;
+struct virtio_pcm_msg;
+
+/**
+ * struct virtio_pcm_substream - VirtIO PCM substream.
+ * @snd: VirtIO sound device.
+ * @nid: Function group node identifier.
+ * @sid: Stream identifier.
+ * @direction: Stream data flow direction (SNDRV_PCM_STREAM_XXX).
+ * @features: Stream VirtIO feature bit map (1 << VIRTIO_SND_PCM_F_XXX).
+ * @substream: Kernel ALSA substream.
+ * @hw: Kernel ALSA substream hardware descriptor.
+ * @elapsed_period: Kernel work to handle the elapsed period state.
+ */
+struct virtio_pcm_substream {
+	struct virtio_snd *snd;
+	u32 nid;
+	u32 sid;
+	u32 direction;
+	u32 features;
+	struct snd_pcm_substream *substream;
+	struct snd_pcm_hardware hw;
+	struct work_struct elapsed_period;
+};
+
+/**
+ * struct virtio_pcm_stream - VirtIO PCM stream.
+ * @substreams: VirtIO substreams belonging to the stream.
+ * @nsubstreams: Number of substreams.
+ */
+struct virtio_pcm_stream {
+	struct virtio_pcm_substream **substreams;
+	u32 nsubstreams;
+};
+
+/**
+ * struct virtio_pcm - VirtIO PCM device.
+ * @list: VirtIO PCM list entry.
+ * @nid: Function group node identifier.
+ * @pcm: Kernel PCM device.
+ * @streams: VirtIO PCM streams (playback and capture).
+ */
+struct virtio_pcm {
+	struct list_head list;
+	u32 nid;
+	struct snd_pcm *pcm;
+	struct virtio_pcm_stream streams[SNDRV_PCM_STREAM_LAST + 1];
+};
+
+int virtsnd_pcm_validate(struct virtio_device *vdev);
+
+int virtsnd_pcm_parse_cfg(struct virtio_snd *snd);
+
+int virtsnd_pcm_build_devs(struct virtio_snd *snd);
+
+struct virtio_pcm *virtsnd_pcm_find(struct virtio_snd *snd, u32 nid);
+
+struct virtio_pcm *virtsnd_pcm_find_or_create(struct virtio_snd *snd, u32 nid);
+
+#endif /* VIRTIO_SND_PCM_H */