ALSA: xen-front: Implement ALSA virtual sound driver

Implement essential initialization of the sound driver:
  - introduce required data structures
  - handle driver registration
  - handle sound card registration
  - register sound driver on backend connection
  - remove sound driver on backend disconnect

Initialize virtual sound card with streams according to the
Xen store configuration.

Implement ALSA driver operations including:
  - manage frontend/backend shared buffers
  - manage Xen bus event channel states

Implement requests from front to back for ALSA
PCM operations.
  - report ALSA period elapsed event: handle XENSND_EVT_CUR_POS
    notifications from the backend when stream position advances
    during playback/capture. The event carries a value of how
    many octets were played/captured at the time of the event.
  - implement explicit stream parameter negotiation between
    backend and frontend: handle XENSND_OP_HW_PARAM_QUERY request
    to read/update configuration space for the parameter given:
    request passes desired parameter interval and the response to
    this request returns min/max interval for the parameter to be used.
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/xen/Makefile

@@ -3,6 +3,7 @@
 snd_xen_front-objs := xen_snd_front.o \
 		      xen_snd_front_cfg.o \
 		      xen_snd_front_evtchnl.o \
-		      xen_snd_front_shbuf.o
+		      xen_snd_front_shbuf.o \
+		      xen_snd_front_alsa.o
 
 obj-$(CONFIG_SND_XEN_FRONTEND) += snd_xen_front.o

sound/xen/xen_snd_front.c

@@ -19,10 +19,189 @@
 #include <xen/interface/io/sndif.h>
 
 #include "xen_snd_front.h"
+#include "xen_snd_front_alsa.h"
 #include "xen_snd_front_evtchnl.h"
+#include "xen_snd_front_shbuf.h"
+
+static struct xensnd_req *
+be_stream_prepare_req(struct xen_snd_front_evtchnl *evtchnl, u8 operation)
+{
+	struct xensnd_req *req;
+
+	req = RING_GET_REQUEST(&evtchnl->u.req.ring,
+			       evtchnl->u.req.ring.req_prod_pvt);
+	req->operation = operation;
+	req->id = evtchnl->evt_next_id++;
+	evtchnl->evt_id = req->id;
+	return req;
+}
+
+static int be_stream_do_io(struct xen_snd_front_evtchnl *evtchnl)
+{
+	if (unlikely(evtchnl->state != EVTCHNL_STATE_CONNECTED))
+		return -EIO;
+
+	reinit_completion(&evtchnl->u.req.completion);
+	xen_snd_front_evtchnl_flush(evtchnl);
+	return 0;
+}
+
+static int be_stream_wait_io(struct xen_snd_front_evtchnl *evtchnl)
+{
+	if (wait_for_completion_timeout(&evtchnl->u.req.completion,
+			msecs_to_jiffies(VSND_WAIT_BACK_MS)) <= 0)
+		return -ETIMEDOUT;
+
+	return evtchnl->u.req.resp_status;
+}
+
+int xen_snd_front_stream_query_hw_param(struct xen_snd_front_evtchnl *evtchnl,
+					struct xensnd_query_hw_param *hw_param_req,
+					struct xensnd_query_hw_param *hw_param_resp)
+{
+	struct xensnd_req *req;
+	int ret;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	mutex_lock(&evtchnl->ring_io_lock);
+	req = be_stream_prepare_req(evtchnl, XENSND_OP_HW_PARAM_QUERY);
+	req->op.hw_param = *hw_param_req;
+	mutex_unlock(&evtchnl->ring_io_lock);
+
+	ret = be_stream_do_io(evtchnl);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	if (ret == 0)
+		*hw_param_resp = evtchnl->u.req.resp.hw_param;
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_snd_front_stream_prepare(struct xen_snd_front_evtchnl *evtchnl,
+				 struct xen_snd_front_shbuf *sh_buf,
+				 u8 format, unsigned int channels,
+				 unsigned int rate, u32 buffer_sz,
+				 u32 period_sz)
+{
+	struct xensnd_req *req;
+	int ret;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	mutex_lock(&evtchnl->ring_io_lock);
+	req = be_stream_prepare_req(evtchnl, XENSND_OP_OPEN);
+	req->op.open.pcm_format = format;
+	req->op.open.pcm_channels = channels;
+	req->op.open.pcm_rate = rate;
+	req->op.open.buffer_sz = buffer_sz;
+	req->op.open.period_sz = period_sz;
+	req->op.open.gref_directory = xen_snd_front_shbuf_get_dir_start(sh_buf);
+	mutex_unlock(&evtchnl->ring_io_lock);
+
+	ret = be_stream_do_io(evtchnl);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_snd_front_stream_close(struct xen_snd_front_evtchnl *evtchnl)
+{
+	struct xensnd_req *req;
+	int ret;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	mutex_lock(&evtchnl->ring_io_lock);
+	req = be_stream_prepare_req(evtchnl, XENSND_OP_CLOSE);
+	mutex_unlock(&evtchnl->ring_io_lock);
+
+	ret = be_stream_do_io(evtchnl);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_snd_front_stream_write(struct xen_snd_front_evtchnl *evtchnl,
+			       unsigned long pos, unsigned long count)
+{
+	struct xensnd_req *req;
+	int ret;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	mutex_lock(&evtchnl->ring_io_lock);
+	req = be_stream_prepare_req(evtchnl, XENSND_OP_WRITE);
+	req->op.rw.length = count;
+	req->op.rw.offset = pos;
+	mutex_unlock(&evtchnl->ring_io_lock);
+
+	ret = be_stream_do_io(evtchnl);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_snd_front_stream_read(struct xen_snd_front_evtchnl *evtchnl,
+			      unsigned long pos, unsigned long count)
+{
+	struct xensnd_req *req;
+	int ret;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	mutex_lock(&evtchnl->ring_io_lock);
+	req = be_stream_prepare_req(evtchnl, XENSND_OP_READ);
+	req->op.rw.length = count;
+	req->op.rw.offset = pos;
+	mutex_unlock(&evtchnl->ring_io_lock);
+
+	ret = be_stream_do_io(evtchnl);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
+
+int xen_snd_front_stream_trigger(struct xen_snd_front_evtchnl *evtchnl,
+				 int type)
+{
+	struct xensnd_req *req;
+	int ret;
+
+	mutex_lock(&evtchnl->u.req.req_io_lock);
+
+	mutex_lock(&evtchnl->ring_io_lock);
+	req = be_stream_prepare_req(evtchnl, XENSND_OP_TRIGGER);
+	req->op.trigger.type = type;
+	mutex_unlock(&evtchnl->ring_io_lock);
+
+	ret = be_stream_do_io(evtchnl);
+
+	if (ret == 0)
+		ret = be_stream_wait_io(evtchnl);
+
+	mutex_unlock(&evtchnl->u.req.req_io_lock);
+	return ret;
+}
 
 static void xen_snd_drv_fini(struct xen_snd_front_info *front_info)
 {
+	xen_snd_front_alsa_fini(front_info);
 	xen_snd_front_evtchnl_free_all(front_info);
 }
 
@@ -45,7 +224,7 @@ static int sndback_initwait(struct xen_snd_front_info *front_info)
 
 static int sndback_connect(struct xen_snd_front_info *front_info)
 {
-	return 0;
+	return xen_snd_front_alsa_init(front_info);
 }
 
 static void sndback_disconnect(struct xen_snd_front_info *front_info)

sound/xen/xen_snd_front.h

@@ -13,15 +13,42 @@
 
 #include "xen_snd_front_cfg.h"
 
+struct xen_snd_front_card_info;
+struct xen_snd_front_evtchnl;
 struct xen_snd_front_evtchnl_pair;
+struct xen_snd_front_shbuf;
+struct xensnd_query_hw_param;
 
 struct xen_snd_front_info {
 	struct xenbus_device *xb_dev;
 
+	struct xen_snd_front_card_info *card_info;
+
 	int num_evt_pairs;
 	struct xen_snd_front_evtchnl_pair *evt_pairs;
 
 	struct xen_front_cfg_card cfg;
 };
 
+int xen_snd_front_stream_query_hw_param(struct xen_snd_front_evtchnl *evtchnl,
+					struct xensnd_query_hw_param *hw_param_req,
+					struct xensnd_query_hw_param *hw_param_resp);
+
+int xen_snd_front_stream_prepare(struct xen_snd_front_evtchnl *evtchnl,
+				 struct xen_snd_front_shbuf *sh_buf,
+				 u8 format, unsigned int channels,
+				 unsigned int rate, u32 buffer_sz,
+				 u32 period_sz);
+
+int xen_snd_front_stream_close(struct xen_snd_front_evtchnl *evtchnl);
+
+int xen_snd_front_stream_write(struct xen_snd_front_evtchnl *evtchnl,
+			       unsigned long pos, unsigned long count);
+
+int xen_snd_front_stream_read(struct xen_snd_front_evtchnl *evtchnl,
+			      unsigned long pos, unsigned long count);
+
+int xen_snd_front_stream_trigger(struct xen_snd_front_evtchnl *evtchnl,
+				 int type);
+
 #endif /* __XEN_SND_FRONT_H */

sound/xen/xen_snd_front_alsa.c

+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#include <linux/platform_device.h>
+
+#include <sound/core.h>
+#include <sound/pcm.h>
+#include <sound/pcm_params.h>
+
+#include <xen/xenbus.h>
+
+#include "xen_snd_front.h"
+#include "xen_snd_front_alsa.h"
+#include "xen_snd_front_cfg.h"
+#include "xen_snd_front_evtchnl.h"
+#include "xen_snd_front_shbuf.h"
+
+struct xen_snd_front_pcm_stream_info {
+	struct xen_snd_front_info *front_info;
+	struct xen_snd_front_evtchnl_pair *evt_pair;
+	struct xen_snd_front_shbuf sh_buf;
+	int index;
+
+	bool is_open;
+	struct snd_pcm_hardware pcm_hw;
+
+	/* Number of processed frames as reported by the backend. */
+	snd_pcm_uframes_t be_cur_frame;
+	/* Current HW pointer to be reported via .period callback. */
+	atomic_t hw_ptr;
+	/* Modulo of the number of processed frames - for period detection. */
+	u32 out_frames;
+};
+
+struct xen_snd_front_pcm_instance_info {
+	struct xen_snd_front_card_info *card_info;
+	struct snd_pcm *pcm;
+	struct snd_pcm_hardware pcm_hw;
+	int num_pcm_streams_pb;
+	struct xen_snd_front_pcm_stream_info *streams_pb;
+	int num_pcm_streams_cap;
+	struct xen_snd_front_pcm_stream_info *streams_cap;
+};
+
+struct xen_snd_front_card_info {
+	struct xen_snd_front_info *front_info;
+	struct snd_card *card;
+	struct snd_pcm_hardware pcm_hw;
+	int num_pcm_instances;
+	struct xen_snd_front_pcm_instance_info *pcm_instances;
+};
+
+struct alsa_sndif_sample_format {
+	u8 sndif;
+	snd_pcm_format_t alsa;
+};
+
+struct alsa_sndif_hw_param {
+	u8 sndif;
+	snd_pcm_hw_param_t alsa;
+};
+
+static const struct alsa_sndif_sample_format ALSA_SNDIF_FORMATS[] = {
+	{
+		.sndif = XENSND_PCM_FORMAT_U8,
+		.alsa = SNDRV_PCM_FORMAT_U8
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_S8,
+		.alsa = SNDRV_PCM_FORMAT_S8
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_U16_LE,
+		.alsa = SNDRV_PCM_FORMAT_U16_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_U16_BE,
+		.alsa = SNDRV_PCM_FORMAT_U16_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_S16_LE,
+		.alsa = SNDRV_PCM_FORMAT_S16_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_S16_BE,
+		.alsa = SNDRV_PCM_FORMAT_S16_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_U24_LE,
+		.alsa = SNDRV_PCM_FORMAT_U24_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_U24_BE,
+		.alsa = SNDRV_PCM_FORMAT_U24_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_S24_LE,
+		.alsa = SNDRV_PCM_FORMAT_S24_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_S24_BE,
+		.alsa = SNDRV_PCM_FORMAT_S24_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_U32_LE,
+		.alsa = SNDRV_PCM_FORMAT_U32_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_U32_BE,
+		.alsa = SNDRV_PCM_FORMAT_U32_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_S32_LE,
+		.alsa = SNDRV_PCM_FORMAT_S32_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_S32_BE,
+		.alsa = SNDRV_PCM_FORMAT_S32_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_A_LAW,
+		.alsa = SNDRV_PCM_FORMAT_A_LAW
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_MU_LAW,
+		.alsa = SNDRV_PCM_FORMAT_MU_LAW
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_F32_LE,
+		.alsa = SNDRV_PCM_FORMAT_FLOAT_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_F32_BE,
+		.alsa = SNDRV_PCM_FORMAT_FLOAT_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_F64_LE,
+		.alsa = SNDRV_PCM_FORMAT_FLOAT64_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_F64_BE,
+		.alsa = SNDRV_PCM_FORMAT_FLOAT64_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_IEC958_SUBFRAME_LE,
+		.alsa = SNDRV_PCM_FORMAT_IEC958_SUBFRAME_LE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_IEC958_SUBFRAME_BE,
+		.alsa = SNDRV_PCM_FORMAT_IEC958_SUBFRAME_BE
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_IMA_ADPCM,
+		.alsa = SNDRV_PCM_FORMAT_IMA_ADPCM
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_MPEG,
+		.alsa = SNDRV_PCM_FORMAT_MPEG
+	},
+	{
+		.sndif = XENSND_PCM_FORMAT_GSM,
+		.alsa = SNDRV_PCM_FORMAT_GSM
+	},
+};
+
+static int to_sndif_format(snd_pcm_format_t format)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(ALSA_SNDIF_FORMATS); i++)
+		if (ALSA_SNDIF_FORMATS[i].alsa == format)
+			return ALSA_SNDIF_FORMATS[i].sndif;
+
+	return -EINVAL;
+}
+
+static u64 to_sndif_formats_mask(u64 alsa_formats)
+{
+	u64 mask;
+	int i;
+
+	mask = 0;
+	for (i = 0; i < ARRAY_SIZE(ALSA_SNDIF_FORMATS); i++)
+		if (1 << ALSA_SNDIF_FORMATS[i].alsa & alsa_formats)
+			mask |= 1 << ALSA_SNDIF_FORMATS[i].sndif;
+
+	return mask;
+}
+
+static u64 to_alsa_formats_mask(u64 sndif_formats)
+{
+	u64 mask;
+	int i;
+
+	mask = 0;
+	for (i = 0; i < ARRAY_SIZE(ALSA_SNDIF_FORMATS); i++)
+		if (1 << ALSA_SNDIF_FORMATS[i].sndif & sndif_formats)
+			mask |= 1 << ALSA_SNDIF_FORMATS[i].alsa;
+
+	return mask;
+}
+
+static void stream_clear(struct xen_snd_front_pcm_stream_info *stream)
+{
+	stream->is_open = false;
+	stream->be_cur_frame = 0;
+	stream->out_frames = 0;
+	atomic_set(&stream->hw_ptr, 0);
+	xen_snd_front_evtchnl_pair_clear(stream->evt_pair);
+	xen_snd_front_shbuf_clear(&stream->sh_buf);
+}
+
+static void stream_free(struct xen_snd_front_pcm_stream_info *stream)
+{
+	xen_snd_front_shbuf_free(&stream->sh_buf);
+	stream_clear(stream);
+}
+
+static struct xen_snd_front_pcm_stream_info *
+stream_get(struct snd_pcm_substream *substream)
+{
+	struct xen_snd_front_pcm_instance_info *pcm_instance =
+			snd_pcm_substream_chip(substream);
+	struct xen_snd_front_pcm_stream_info *stream;
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		stream = &pcm_instance->streams_pb[substream->number];
+	else
+		stream = &pcm_instance->streams_cap[substream->number];
+
+	return stream;
+}
+
+static int alsa_hw_rule(struct snd_pcm_hw_params *params,
+			struct snd_pcm_hw_rule *rule)
+{
+	struct xen_snd_front_pcm_stream_info *stream = rule->private;
+	struct device *dev = &stream->front_info->xb_dev->dev;
+	struct snd_mask *formats =
+			hw_param_mask(params, SNDRV_PCM_HW_PARAM_FORMAT);
+	struct snd_interval *rates =
+			hw_param_interval(params, SNDRV_PCM_HW_PARAM_RATE);
+	struct snd_interval *channels =
+			hw_param_interval(params, SNDRV_PCM_HW_PARAM_CHANNELS);
+	struct snd_interval *period =
+			hw_param_interval(params,
+					  SNDRV_PCM_HW_PARAM_PERIOD_SIZE);
+	struct snd_interval *buffer =
+			hw_param_interval(params,
+					  SNDRV_PCM_HW_PARAM_BUFFER_SIZE);
+	struct xensnd_query_hw_param req;
+	struct xensnd_query_hw_param resp;
+	struct snd_interval interval;
+	struct snd_mask mask;
+	u64 sndif_formats;
+	int changed, ret;
+
+	/* Collect all the values we need for the query. */
+
+	req.formats = to_sndif_formats_mask((u64)formats->bits[0] |
+					    (u64)(formats->bits[1]) << 32);
+
+	req.rates.min = rates->min;
+	req.rates.max = rates->max;
+
+	req.channels.min = channels->min;
+	req.channels.max = channels->max;
+
+	req.buffer.min = buffer->min;
+	req.buffer.max = buffer->max;
+
+	req.period.min = period->min;
+	req.period.max = period->max;
+
+	ret = xen_snd_front_stream_query_hw_param(&stream->evt_pair->req,
+						  &req, &resp);
+	if (ret < 0) {
+		/* Check if this is due to backend communication error. */
+		if (ret == -EIO || ret == -ETIMEDOUT)
+			dev_err(dev, "Failed to query ALSA HW parameters\n");
+		return ret;
+	}
+
+	/* Refine HW parameters after the query. */
+	changed  = 0;
+
+	sndif_formats = to_alsa_formats_mask(resp.formats);
+	snd_mask_none(&mask);
+	mask.bits[0] = (u32)sndif_formats;
+	mask.bits[1] = (u32)(sndif_formats >> 32);
+	ret = snd_mask_refine(formats, &mask);
+	if (ret < 0)
+		return ret;
+	changed |= ret;
+
+	interval.openmin = 0;
+	interval.openmax = 0;
+	interval.integer = 1;
+
+	interval.min = resp.rates.min;
+	interval.max = resp.rates.max;
+	ret = snd_interval_refine(rates, &interval);
+	if (ret < 0)
+		return ret;
+	changed |= ret;
+
+	interval.min = resp.channels.min;
+	interval.max = resp.channels.max;
+	ret = snd_interval_refine(channels, &interval);
+	if (ret < 0)
+		return ret;
+	changed |= ret;
+
+	interval.min = resp.buffer.min;
+	interval.max = resp.buffer.max;
+	ret = snd_interval_refine(buffer, &interval);
+	if (ret < 0)
+		return ret;
+	changed |= ret;
+
+	interval.min = resp.period.min;
+	interval.max = resp.period.max;
+	ret = snd_interval_refine(period, &interval);
+	if (ret < 0)
+		return ret;
+	changed |= ret;
+
+	return changed;
+}
+
+static int alsa_open(struct snd_pcm_substream *substream)
+{
+	struct xen_snd_front_pcm_instance_info *pcm_instance =
+			snd_pcm_substream_chip(substream);
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+	struct snd_pcm_runtime *runtime = substream->runtime;
+	struct xen_snd_front_info *front_info =
+			pcm_instance->card_info->front_info;
+	struct device *dev = &front_info->xb_dev->dev;
+	int ret;
+
+	/*
+	 * Return our HW properties: override defaults with those configured
+	 * via XenStore.
+	 */
+	runtime->hw = stream->pcm_hw;
+	runtime->hw.info &= ~(SNDRV_PCM_INFO_MMAP |
+			      SNDRV_PCM_INFO_MMAP_VALID |
+			      SNDRV_PCM_INFO_DOUBLE |
+			      SNDRV_PCM_INFO_BATCH |
+			      SNDRV_PCM_INFO_NONINTERLEAVED |
+			      SNDRV_PCM_INFO_RESUME |
+			      SNDRV_PCM_INFO_PAUSE);
+	runtime->hw.info |= SNDRV_PCM_INFO_INTERLEAVED;
+
+	stream->evt_pair = &front_info->evt_pairs[stream->index];
+
+	stream->front_info = front_info;
+
+	stream->evt_pair->evt.u.evt.substream = substream;
+
+	stream_clear(stream);
+
+	xen_snd_front_evtchnl_pair_set_connected(stream->evt_pair, true);
+
+	ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_FORMAT,
+				  alsa_hw_rule, stream,
+				  SNDRV_PCM_HW_PARAM_FORMAT, -1);
+	if (ret) {
+		dev_err(dev, "Failed to add HW rule for SNDRV_PCM_HW_PARAM_FORMAT\n");
+		return ret;
+	}
+
+	ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_RATE,
+				  alsa_hw_rule, stream,
+				  SNDRV_PCM_HW_PARAM_RATE, -1);
+	if (ret) {
+		dev_err(dev, "Failed to add HW rule for SNDRV_PCM_HW_PARAM_RATE\n");
+		return ret;
+	}
+
+	ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_CHANNELS,
+				  alsa_hw_rule, stream,
+				  SNDRV_PCM_HW_PARAM_CHANNELS, -1);
+	if (ret) {
+		dev_err(dev, "Failed to add HW rule for SNDRV_PCM_HW_PARAM_CHANNELS\n");
+		return ret;
+	}
+
+	ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_PERIOD_SIZE,
+				  alsa_hw_rule, stream,
+				  SNDRV_PCM_HW_PARAM_PERIOD_SIZE, -1);
+	if (ret) {
+		dev_err(dev, "Failed to add HW rule for SNDRV_PCM_HW_PARAM_PERIOD_SIZE\n");
+		return ret;
+	}
+
+	ret = snd_pcm_hw_rule_add(runtime, 0, SNDRV_PCM_HW_PARAM_BUFFER_SIZE,
+				  alsa_hw_rule, stream,
+				  SNDRV_PCM_HW_PARAM_BUFFER_SIZE, -1);
+	if (ret) {
+		dev_err(dev, "Failed to add HW rule for SNDRV_PCM_HW_PARAM_BUFFER_SIZE\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static int alsa_close(struct snd_pcm_substream *substream)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+
+	xen_snd_front_evtchnl_pair_set_connected(stream->evt_pair, false);
+	return 0;
+}
+
+static int alsa_hw_params(struct snd_pcm_substream *substream,
+			  struct snd_pcm_hw_params *params)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+	int ret;
+
+	/*
+	 * This callback may be called multiple times,
+	 * so free the previously allocated shared buffer if any.
+	 */
+	stream_free(stream);
+
+	ret = xen_snd_front_shbuf_alloc(stream->front_info->xb_dev,
+					&stream->sh_buf,
+					params_buffer_bytes(params));
+	if (ret < 0) {
+		stream_free(stream);
+		dev_err(&stream->front_info->xb_dev->dev,
+			"Failed to allocate buffers for stream with index %d\n",
+			stream->index);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int alsa_hw_free(struct snd_pcm_substream *substream)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+	int ret;
+
+	ret = xen_snd_front_stream_close(&stream->evt_pair->req);
+	stream_free(stream);
+	return ret;
+}
+
+static int alsa_prepare(struct snd_pcm_substream *substream)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+
+	if (!stream->is_open) {
+		struct snd_pcm_runtime *runtime = substream->runtime;
+		u8 sndif_format;
+		int ret;
+
+		sndif_format = to_sndif_format(runtime->format);
+		if (sndif_format < 0) {
+			dev_err(&stream->front_info->xb_dev->dev,
+				"Unsupported sample format: %d\n",
+				runtime->format);
+			return sndif_format;
+		}
+
+		ret = xen_snd_front_stream_prepare(&stream->evt_pair->req,
+						   &stream->sh_buf,
+						   sndif_format,
+						   runtime->channels,
+						   runtime->rate,
+						   snd_pcm_lib_buffer_bytes(substream),
+						   snd_pcm_lib_period_bytes(substream));
+		if (ret < 0)
+			return ret;
+
+		stream->is_open = true;
+	}
+
+	return 0;
+}
+
+static int alsa_trigger(struct snd_pcm_substream *substream, int cmd)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+	int type;
+
+	switch (cmd) {
+	case SNDRV_PCM_TRIGGER_START:
+		type = XENSND_OP_TRIGGER_START;
+		break;
+
+	case SNDRV_PCM_TRIGGER_RESUME:
+		type = XENSND_OP_TRIGGER_RESUME;
+		break;
+
+	case SNDRV_PCM_TRIGGER_STOP:
+		type = XENSND_OP_TRIGGER_STOP;
+		break;
+
+	case SNDRV_PCM_TRIGGER_SUSPEND:
+		type = XENSND_OP_TRIGGER_PAUSE;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	return xen_snd_front_stream_trigger(&stream->evt_pair->req, type);
+}
+
+void xen_snd_front_alsa_handle_cur_pos(struct xen_snd_front_evtchnl *evtchnl,
+				       u64 pos_bytes)
+{
+	struct snd_pcm_substream *substream = evtchnl->u.evt.substream;
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+	snd_pcm_uframes_t delta, new_hw_ptr, cur_frame;
+
+	cur_frame = bytes_to_frames(substream->runtime, pos_bytes);
+
+	delta = cur_frame - stream->be_cur_frame;
+	stream->be_cur_frame = cur_frame;
+
+	new_hw_ptr = (snd_pcm_uframes_t)atomic_read(&stream->hw_ptr);
+	new_hw_ptr = (new_hw_ptr + delta) % substream->runtime->buffer_size;
+	atomic_set(&stream->hw_ptr, (int)new_hw_ptr);
+
+	stream->out_frames += delta;
+	if (stream->out_frames > substream->runtime->period_size) {
+		stream->out_frames %= substream->runtime->period_size;
+		snd_pcm_period_elapsed(substream);
+	}
+}
+
+static snd_pcm_uframes_t alsa_pointer(struct snd_pcm_substream *substream)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+
+	return (snd_pcm_uframes_t)atomic_read(&stream->hw_ptr);
+}
+
+static int alsa_pb_copy_user(struct snd_pcm_substream *substream,
+			     int channel, unsigned long pos, void __user *src,
+			     unsigned long count)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+
+	if (unlikely(pos + count > stream->sh_buf.buffer_sz))
+		return -EINVAL;
+
+	if (copy_from_user(stream->sh_buf.buffer + pos, src, count))
+		return -EFAULT;
+
+	return xen_snd_front_stream_write(&stream->evt_pair->req, pos, count);
+}
+
+static int alsa_pb_copy_kernel(struct snd_pcm_substream *substream,
+			       int channel, unsigned long pos, void *src,
+			       unsigned long count)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+
+	if (unlikely(pos + count > stream->sh_buf.buffer_sz))
+		return -EINVAL;
+
+	memcpy(stream->sh_buf.buffer + pos, src, count);
+
+	return xen_snd_front_stream_write(&stream->evt_pair->req, pos, count);
+}
+
+static int alsa_cap_copy_user(struct snd_pcm_substream *substream,
+			      int channel, unsigned long pos, void __user *dst,
+			      unsigned long count)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+	int ret;
+
+	if (unlikely(pos + count > stream->sh_buf.buffer_sz))
+		return -EINVAL;
+
+	ret = xen_snd_front_stream_read(&stream->evt_pair->req, pos, count);
+	if (ret < 0)
+		return ret;
+
+	return copy_to_user(dst, stream->sh_buf.buffer + pos, count) ?
+		-EFAULT : 0;
+}
+
+static int alsa_cap_copy_kernel(struct snd_pcm_substream *substream,
+				int channel, unsigned long pos, void *dst,
+				unsigned long count)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+	int ret;
+
+	if (unlikely(pos + count > stream->sh_buf.buffer_sz))
+		return -EINVAL;
+
+	ret = xen_snd_front_stream_read(&stream->evt_pair->req, pos, count);
+	if (ret < 0)
+		return ret;
+
+	memcpy(dst, stream->sh_buf.buffer + pos, count);
+
+	return 0;
+}
+
+static int alsa_pb_fill_silence(struct snd_pcm_substream *substream,
+				int channel, unsigned long pos,
+				unsigned long count)
+{
+	struct xen_snd_front_pcm_stream_info *stream = stream_get(substream);
+
+	if (unlikely(pos + count > stream->sh_buf.buffer_sz))
+		return -EINVAL;
+
+	memset(stream->sh_buf.buffer + pos, 0, count);
+
+	return xen_snd_front_stream_write(&stream->evt_pair->req, pos, count);
+}
+
+/*
+ * FIXME: The mmaped data transfer is asynchronous and there is no
+ * ack signal from user-space when it is done. This is the
+ * reason it is not implemented in the PV driver as we do need
+ * to know when the buffer can be transferred to the backend.
+ */
+
+static struct snd_pcm_ops snd_drv_alsa_playback_ops = {
+	.open = alsa_open,
+	.close = alsa_close,
+	.ioctl = snd_pcm_lib_ioctl,
+	.hw_params = alsa_hw_params,
+	.hw_free = alsa_hw_free,
+	.prepare = alsa_prepare,
+	.trigger = alsa_trigger,
+	.pointer = alsa_pointer,
+	.copy_user = alsa_pb_copy_user,
+	.copy_kernel = alsa_pb_copy_kernel,
+	.fill_silence = alsa_pb_fill_silence,
+};
+
+static struct snd_pcm_ops snd_drv_alsa_capture_ops = {
+	.open = alsa_open,
+	.close = alsa_close,
+	.ioctl = snd_pcm_lib_ioctl,
+	.hw_params = alsa_hw_params,
+	.hw_free = alsa_hw_free,
+	.prepare = alsa_prepare,
+	.trigger = alsa_trigger,
+	.pointer = alsa_pointer,
+	.copy_user = alsa_cap_copy_user,
+	.copy_kernel = alsa_cap_copy_kernel,
+};
+
+static int new_pcm_instance(struct xen_snd_front_card_info *card_info,
+			    struct xen_front_cfg_pcm_instance *instance_cfg,
+			    struct xen_snd_front_pcm_instance_info *pcm_instance_info)
+{
+	struct snd_pcm *pcm;
+	int ret, i;
+
+	dev_dbg(&card_info->front_info->xb_dev->dev,
+		"New PCM device \"%s\" with id %d playback %d capture %d",
+		instance_cfg->name,
+		instance_cfg->device_id,
+		instance_cfg->num_streams_pb,
+		instance_cfg->num_streams_cap);
+
+	pcm_instance_info->card_info = card_info;
+
+	pcm_instance_info->pcm_hw = instance_cfg->pcm_hw;
+
+	if (instance_cfg->num_streams_pb) {
+		pcm_instance_info->streams_pb =
+				devm_kcalloc(&card_info->card->card_dev,
+					     instance_cfg->num_streams_pb,
+					     sizeof(struct xen_snd_front_pcm_stream_info),
+					     GFP_KERNEL);
+		if (!pcm_instance_info->streams_pb)
+			return -ENOMEM;
+	}
+
+	if (instance_cfg->num_streams_cap) {
+		pcm_instance_info->streams_cap =
+				devm_kcalloc(&card_info->card->card_dev,
+					     instance_cfg->num_streams_cap,
+					     sizeof(struct xen_snd_front_pcm_stream_info),
+					     GFP_KERNEL);
+		if (!pcm_instance_info->streams_cap)
+			return -ENOMEM;
+	}
+
+	pcm_instance_info->num_pcm_streams_pb =
+			instance_cfg->num_streams_pb;
+	pcm_instance_info->num_pcm_streams_cap =
+			instance_cfg->num_streams_cap;
+
+	for (i = 0; i < pcm_instance_info->num_pcm_streams_pb; i++) {
+		pcm_instance_info->streams_pb[i].pcm_hw =
+			instance_cfg->streams_pb[i].pcm_hw;
+		pcm_instance_info->streams_pb[i].index =
+			instance_cfg->streams_pb[i].index;
+	}
+
+	for (i = 0; i < pcm_instance_info->num_pcm_streams_cap; i++) {
+		pcm_instance_info->streams_cap[i].pcm_hw =
+			instance_cfg->streams_cap[i].pcm_hw;
+		pcm_instance_info->streams_cap[i].index =
+			instance_cfg->streams_cap[i].index;
+	}
+
+	ret = snd_pcm_new(card_info->card, instance_cfg->name,
+			  instance_cfg->device_id,
+			  instance_cfg->num_streams_pb,
+			  instance_cfg->num_streams_cap,
+			  &pcm);
+	if (ret < 0)
+		return ret;
+
+	pcm->private_data = pcm_instance_info;
+	pcm->info_flags = 0;
+	/* we want to handle all PCM operations in non-atomic context */
+	pcm->nonatomic = true;
+	strncpy(pcm->name, "Virtual card PCM", sizeof(pcm->name));
+
+	if (instance_cfg->num_streams_pb)
+		snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK,
+				&snd_drv_alsa_playback_ops);
+
+	if (instance_cfg->num_streams_cap)
+		snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE,
+				&snd_drv_alsa_capture_ops);
+
+	pcm_instance_info->pcm = pcm;
+	return 0;
+}
+
+int xen_snd_front_alsa_init(struct xen_snd_front_info *front_info)
+{
+	struct device *dev = &front_info->xb_dev->dev;
+	struct xen_front_cfg_card *cfg = &front_info->cfg;
+	struct xen_snd_front_card_info *card_info;
+	struct snd_card *card;
+	int ret, i;
+
+	dev_dbg(dev, "Creating virtual sound card\n");
+
+	ret = snd_card_new(dev, 0, XENSND_DRIVER_NAME, THIS_MODULE,
+			   sizeof(struct xen_snd_front_card_info), &card);
+	if (ret < 0)
+		return ret;
+
+	card_info = card->private_data;
+	card_info->front_info = front_info;
+	front_info->card_info = card_info;
+	card_info->card = card;
+	card_info->pcm_instances =
+			devm_kcalloc(dev, cfg->num_pcm_instances,
+				     sizeof(struct xen_snd_front_pcm_instance_info),
+				     GFP_KERNEL);
+	if (!card_info->pcm_instances) {
+		ret = -ENOMEM;
+		goto fail;
+	}
+
+	card_info->num_pcm_instances = cfg->num_pcm_instances;
+	card_info->pcm_hw = cfg->pcm_hw;
+
+	for (i = 0; i < cfg->num_pcm_instances; i++) {
+		ret = new_pcm_instance(card_info, &cfg->pcm_instances[i],
+				       &card_info->pcm_instances[i]);
+		if (ret < 0)
+			goto fail;
+	}
+
+	strncpy(card->driver, XENSND_DRIVER_NAME, sizeof(card->driver));
+	strncpy(card->shortname, cfg->name_short, sizeof(card->shortname));
+	strncpy(card->longname, cfg->name_long, sizeof(card->longname));
+
+	ret = snd_card_register(card);
+	if (ret < 0)
+		goto fail;
+
+	return 0;
+
+fail:
+	snd_card_free(card);
+	return ret;
+}
+
+void xen_snd_front_alsa_fini(struct xen_snd_front_info *front_info)
+{
+	struct xen_snd_front_card_info *card_info;
+	struct snd_card *card;
+
+	card_info = front_info->card_info;
+	if (!card_info)
+		return;
+
+	card = card_info->card;
+	if (!card)
+		return;
+
+	dev_dbg(&front_info->xb_dev->dev, "Removing virtual sound card %d\n",
+		card->number);
+	snd_card_free(card);
+
+	/* Card_info will be freed when destroying front_info->xb_dev->dev. */
+	card_info->card = NULL;
+}

sound/xen/xen_snd_front_alsa.h

+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
+ */
+
+#ifndef __XEN_SND_FRONT_ALSA_H
+#define __XEN_SND_FRONT_ALSA_H
+
+struct xen_snd_front_info;
+
+int xen_snd_front_alsa_init(struct xen_snd_front_info *front_info);
+
+void xen_snd_front_alsa_fini(struct xen_snd_front_info *front_info);
+
+void xen_snd_front_alsa_handle_cur_pos(struct xen_snd_front_evtchnl *evtchnl,
+				       u64 pos_bytes);
+
+#endif /* __XEN_SND_FRONT_ALSA_H */

sound/xen/xen_snd_front_evtchnl.c

@@ -14,6 +14,7 @@
 #include <xen/xenbus.h>
 
 #include "xen_snd_front.h"
+#include "xen_snd_front_alsa.h"
 #include "xen_snd_front_cfg.h"
 #include "xen_snd_front_evtchnl.h"
 
@@ -118,7 +119,8 @@ static irqreturn_t evtchnl_interrupt_evt(int irq, void *dev_id)
 
 		switch (event->type) {
 		case XENSND_EVT_CUR_POS:
-			/* Do nothing at the moment. */
+			xen_snd_front_alsa_handle_cur_pos(channel,
+							  event->op.cur_pos.position);
 			break;
 		}
 	}