From: Oleksandr Andrushchenko <oleksandr_andrushche...@epam.com>

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_andrushche...@epam.com>
---
 sound/xen/Makefile                |   3 +-
 sound/xen/xen_snd_front.c         | 193 ++++++++-
 sound/xen/xen_snd_front.h         |  28 ++
 sound/xen/xen_snd_front_alsa.c    | 830 ++++++++++++++++++++++++++++++++++++++
 sound/xen/xen_snd_front_alsa.h    |  23 ++
 sound/xen/xen_snd_front_evtchnl.c |   6 +-
 6 files changed, 1080 insertions(+), 3 deletions(-)
 create mode 100644 sound/xen/xen_snd_front_alsa.c
 create mode 100644 sound/xen/xen_snd_front_alsa.h

diff --git a/sound/xen/Makefile b/sound/xen/Makefile
index f028bc30af5d..1e6470ecc2f2 100644
--- a/sound/xen/Makefile
+++ b/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
diff --git a/sound/xen/xen_snd_front.c b/sound/xen/xen_snd_front.c
index 0569c6c596a3..1fef253ea21a 100644
--- a/sound/xen/xen_snd_front.c
+++ b/sound/xen/xen_snd_front.c
@@ -19,10 +19,201 @@
 #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 xen_snd_front_info *front_info = evtchnl->front_info;
+       struct xensnd_req *req;
+       unsigned long flags;
+       int ret;
+
+       mutex_lock(&evtchnl->u.req.req_io_lock);
+
+       spin_lock_irqsave(&front_info->io_lock, flags);
+       req = be_stream_prepare_req(evtchnl, XENSND_OP_HW_PARAM_QUERY);
+       req->op.hw_param = *hw_param_req;
+
+       ret = be_stream_do_io(evtchnl);
+       spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+       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 xen_snd_front_info *front_info = evtchnl->front_info;
+       struct xensnd_req *req;
+       unsigned long flags;
+       int ret;
+
+       mutex_lock(&evtchnl->u.req.req_io_lock);
+
+       spin_lock_irqsave(&front_info->io_lock, flags);
+       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);
+
+       ret = be_stream_do_io(evtchnl);
+       spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+       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 xen_snd_front_info *front_info = evtchnl->front_info;
+       struct xensnd_req *req;
+       unsigned long flags;
+       int ret;
+
+       mutex_lock(&evtchnl->u.req.req_io_lock);
+
+       spin_lock_irqsave(&front_info->io_lock, flags);
+       req = be_stream_prepare_req(evtchnl, XENSND_OP_CLOSE);
+
+       ret = be_stream_do_io(evtchnl);
+       spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+       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 xen_snd_front_info *front_info = evtchnl->front_info;
+       struct xensnd_req *req;
+       unsigned long flags;
+       int ret;
+
+       mutex_lock(&evtchnl->u.req.req_io_lock);
+
+       spin_lock_irqsave(&front_info->io_lock, flags);
+       req = be_stream_prepare_req(evtchnl, XENSND_OP_WRITE);
+       req->op.rw.length = count;
+       req->op.rw.offset = pos;
+
+       ret = be_stream_do_io(evtchnl);
+       spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+       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 xen_snd_front_info *front_info = evtchnl->front_info;
+       struct xensnd_req *req;
+       unsigned long flags;
+       int ret;
+
+       mutex_lock(&evtchnl->u.req.req_io_lock);
+
+       spin_lock_irqsave(&front_info->io_lock, flags);
+       req = be_stream_prepare_req(evtchnl, XENSND_OP_READ);
+       req->op.rw.length = count;
+       req->op.rw.offset = pos;
+
+       ret = be_stream_do_io(evtchnl);
+       spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+       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 xen_snd_front_info *front_info = evtchnl->front_info;
+       struct xensnd_req *req;
+       unsigned long flags;
+       int ret;
+
+       mutex_lock(&evtchnl->u.req.req_io_lock);
+
+       spin_lock_irqsave(&front_info->io_lock, flags);
+       req = be_stream_prepare_req(evtchnl, XENSND_OP_TRIGGER);
+       req->op.trigger.type = type;
+
+       ret = be_stream_do_io(evtchnl);
+       spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+       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 +236,7 @@ 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)
diff --git a/sound/xen/xen_snd_front.h b/sound/xen/xen_snd_front.h
index 9c2ffbb4e4b8..7adbdb4d2019 100644
--- a/sound/xen/xen_snd_front.h
+++ b/sound/xen/xen_snd_front.h
@@ -13,17 +13,45 @@
 
 #include "xen_snd_front_cfg.h"
 
+struct 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 card_info *card_info;
+
        /* serializer for backend IO: request/response */
        spinlock_t io_lock;
+
        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 */
diff --git a/sound/xen/xen_snd_front_alsa.c b/sound/xen/xen_snd_front_alsa.c
new file mode 100644
index 000000000000..f524b172750e
--- /dev/null
+++ b/sound/xen/xen_snd_front_alsa.c
@@ -0,0 +1,830 @@
+// SPDX-License-Identifier: GPL-2.0 OR MIT
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushche...@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 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 pcm_instance_info {
+       struct card_info *card_info;
+       struct snd_pcm *pcm;
+       struct snd_pcm_hardware pcm_hw;
+       int num_pcm_streams_pb;
+       struct pcm_stream_info *streams_pb;
+       int num_pcm_streams_cap;
+       struct pcm_stream_info *streams_cap;
+};
+
+struct card_info {
+       struct xen_snd_front_info *front_info;
+       struct snd_card *card;
+       struct snd_pcm_hardware pcm_hw;
+       int num_pcm_instances;
+       struct 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 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 pcm_stream_info *stream)
+{
+       xen_snd_front_shbuf_free(&stream->sh_buf);
+       stream_clear(stream);
+}
+
+static struct pcm_stream_info *stream_get(struct snd_pcm_substream *substream)
+{
+       struct pcm_instance_info *pcm_instance =
+                       snd_pcm_substream_chip(substream);
+       struct 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 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 pcm_instance_info *pcm_instance =
+                       snd_pcm_substream_chip(substream);
+       struct 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;
+       unsigned long flags;
+       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;
+
+       spin_lock_irqsave(&front_info->io_lock, flags);
+
+       stream->evt_pair = &front_info->evt_pairs[stream->index];
+
+       stream->front_info = front_info;
+
+       xen_snd_front_evtchnl_pair_set_connected(stream->evt_pair, true);
+
+       stream->evt_pair->evt.u.evt.substream = substream;
+
+       stream_clear(stream);
+
+       spin_unlock_irqrestore(&front_info->io_lock, flags);
+
+       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 pcm_stream_info *stream = stream_get(substream);
+       unsigned long flags;
+
+       spin_lock_irqsave(&stream->front_info->io_lock, flags);
+
+       xen_snd_front_evtchnl_pair_set_connected(stream->evt_pair, false);
+
+       spin_unlock_irqrestore(&stream->front_info->io_lock, flags);
+       return 0;
+}
+
+static int alsa_hw_params(struct snd_pcm_substream *substream,
+                         struct snd_pcm_hw_params *params)
+{
+       struct 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 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 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 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 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 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 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 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 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 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 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 card_info *card_info,
+                           struct xen_front_cfg_pcm_instance *instance_cfg,
+                           struct 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 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 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 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 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 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 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;
+}
diff --git a/sound/xen/xen_snd_front_alsa.h b/sound/xen/xen_snd_front_alsa.h
new file mode 100644
index 000000000000..18abd9eec967
--- /dev/null
+++ b/sound/xen/xen_snd_front_alsa.h
@@ -0,0 +1,23 @@
+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+
+/*
+ * Xen para-virtual sound device
+ *
+ * Copyright (C) 2016-2018 EPAM Systems Inc.
+ *
+ * Author: Oleksandr Andrushchenko <oleksandr_andrushche...@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 */
diff --git a/sound/xen/xen_snd_front_evtchnl.c 
b/sound/xen/xen_snd_front_evtchnl.c
index 9ece39f938f8..470196518716 100644
--- a/sound/xen/xen_snd_front_evtchnl.c
+++ b/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"
 
@@ -111,7 +112,10 @@ static irqreturn_t evtchnl_interrupt_evt(int irq, void 
*dev_id)
 
                switch (event->type) {
                case XENSND_EVT_CUR_POS:
-                       /* do nothing at the moment */
+                       spin_unlock_irqrestore(&front_info->io_lock, flags);
+                       xen_snd_front_alsa_handle_cur_pos(channel,
+                                                         
event->op.cur_pos.position);
+                       spin_lock_irqsave(&front_info->io_lock, flags);
                        break;
                }
        }
-- 
2.16.2


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