diff --git a/include/xen/interface/io/sndif.h b/include/xen/interface/io/sndif.h
index 5c918276835e..78bb5d9f8d83 100644
--- a/include/xen/interface/io/sndif.h
+++ b/include/xen/interface/io/sndif.h
@@ -36,6 +36,13 @@
 #include "ring.h"
 #include "../grant_table.h"
 
+/*
+ ******************************************************************************
+ *                           Protocol version
+ ******************************************************************************
+ */
+#define XENSND_PROTOCOL_VERSION	2
+
 /*
  ******************************************************************************
  *                  Feature and Parameter Negotiation
@@ -106,6 +113,8 @@
  *
  * /local/domain/1/device/vsnd/0/0/0/ring-ref = "386"
  * /local/domain/1/device/vsnd/0/0/0/event-channel = "15"
+ * /local/domain/1/device/vsnd/0/0/0/evt-ring-ref = "1386"
+ * /local/domain/1/device/vsnd/0/0/0/evt-event-channel = "215"
  *
  *------------------------------ Stream 1, capture ----------------------------
  *
@@ -115,6 +124,8 @@
  *
  * /local/domain/1/device/vsnd/0/0/1/ring-ref = "384"
  * /local/domain/1/device/vsnd/0/0/1/event-channel = "13"
+ * /local/domain/1/device/vsnd/0/0/1/evt-ring-ref = "1384"
+ * /local/domain/1/device/vsnd/0/0/1/evt-event-channel = "213"
  *
  *------------------------------- PCM device 1 --------------------------------
  *
@@ -128,6 +139,8 @@
  *
  * /local/domain/1/device/vsnd/0/1/0/ring-ref = "387"
  * /local/domain/1/device/vsnd/0/1/0/event-channel = "151"
+ * /local/domain/1/device/vsnd/0/1/0/evt-ring-ref = "1387"
+ * /local/domain/1/device/vsnd/0/1/0/evt-event-channel = "351"
  *
  *------------------------------- PCM device 2 --------------------------------
  *
@@ -140,6 +153,8 @@
  *
  * /local/domain/1/device/vsnd/0/2/0/ring-ref = "389"
  * /local/domain/1/device/vsnd/0/2/0/event-channel = "152"
+ * /local/domain/1/device/vsnd/0/2/0/evt-ring-ref = "1389"
+ * /local/domain/1/device/vsnd/0/2/0/evt-event-channel = "452"
  *
  ******************************************************************************
  *                            Backend XenBus Nodes
@@ -285,6 +300,23 @@
  *      The Xen grant reference granting permission for the backend to map
  *      a sole page in a single page sized ring buffer.
  *
+ *--------------------- Stream Event Transport Parameters ---------------------
+ *
+ * This communication path is used to deliver asynchronous events from backend
+ * to frontend, set up per stream.
+ *
+ * evt-event-channel
+ *      Values:         <uint32_t>
+ *
+ *      The identifier of the Xen event channel used to signal activity
+ *      in the ring buffer.
+ *
+ * evt-ring-ref
+ *      Values:         <uint32_t>
+ *
+ *      The Xen grant reference granting permission for the backend to map
+ *      a sole page in a single page sized ring buffer.
+ *
  ******************************************************************************
  *                               STATE DIAGRAMS
  ******************************************************************************
@@ -432,6 +464,20 @@
 #define XENSND_OP_GET_VOLUME		5
 #define XENSND_OP_MUTE			6
 #define XENSND_OP_UNMUTE		7
+#define XENSND_OP_TRIGGER		8
+#define XENSND_OP_HW_PARAM_QUERY	9
+
+#define XENSND_OP_TRIGGER_START		0
+#define XENSND_OP_TRIGGER_PAUSE		1
+#define XENSND_OP_TRIGGER_STOP		2
+#define XENSND_OP_TRIGGER_RESUME	3
+
+/*
+ ******************************************************************************
+ *                                 EVENT CODES
+ ******************************************************************************
+ */
+#define XENSND_EVT_CUR_POS		0
 
 /*
  ******************************************************************************
@@ -448,6 +494,8 @@
 #define XENSND_FIELD_VCARD_LONG_NAME	"long-name"
 #define XENSND_FIELD_RING_REF		"ring-ref"
 #define XENSND_FIELD_EVT_CHNL		"event-channel"
+#define XENSND_FIELD_EVT_RING_REF	"evt-ring-ref"
+#define XENSND_FIELD_EVT_EVT_CHNL	"evt-event-channel"
 #define XENSND_FIELD_DEVICE_NAME	"name"
 #define XENSND_FIELD_TYPE		"type"
 #define XENSND_FIELD_STREAM_UNIQUE_ID	"unique-id"
@@ -526,7 +574,7 @@
  *
  *---------------------------------- Requests ---------------------------------
  *
- * All request packets have the same length (32 octets)
+ * All request packets have the same length (64 octets)
  * All request packets have common header:
  *         0                1                 2               3        octet
  * +----------------+----------------+----------------+----------------+
@@ -559,11 +607,13 @@
  * +----------------+----------------+----------------+----------------+
  * |                           gref_directory                          | 24
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 28
+ * |                             period_sz                             | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 32
  * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 32
+ * |                             reserved                              | 64
  * +----------------+----------------+----------------+----------------+
  *
  * pcm_rate - uint32_t, stream data rate, Hz
@@ -571,6 +621,14 @@
  * pcm_channels - uint8_t, number of channels of this stream,
  *   [channels-min; channels-max]
  * buffer_sz - uint32_t, buffer size to be allocated, octets
+ * period_sz - uint32_t, event period size, octets
+ *   This is the requested value of the period at which frontend would
+ *   like to receive XENSND_EVT_CUR_POS notifications from the backend when
+ *   stream position advances during playback/capture.
+ *   It shows how many octets are expected to be played/captured before
+ *   sending such an event.
+ *   If set to 0 no XENSND_EVT_CUR_POS events are sent by the backend.
+ *
  * gref_directory - grant_ref_t, a reference to the first shared page
  *   describing shared buffer references. At least one page exists. If shared
  *   buffer size  (buffer_sz) exceeds what can be addressed by this single page,
@@ -585,6 +643,7 @@ struct xensnd_open_req {
 	uint16_t reserved;
 	uint32_t buffer_sz;
 	grant_ref_t gref_directory;
+	uint32_t period_sz;
 };
 
 /*
@@ -632,7 +691,7 @@ struct xensnd_page_directory {
  * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 32
+ * |                             reserved                              | 64
  * +----------------+----------------+----------------+----------------+
  *
  * Request read/write - used for read (for capture) or write (for playback):
@@ -650,7 +709,7 @@ struct xensnd_page_directory {
  * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 32
+ * |                             reserved                              | 64
  * +----------------+----------------+----------------+----------------+
  *
  * operation - XENSND_OP_READ for read or XENSND_OP_WRITE for write
@@ -673,9 +732,11 @@ struct xensnd_rw_req {
  * +----------------+----------------+----------------+----------------+
  * |                              length                               | 16
  * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 32
+ * |                             reserved                              | 64
  * +----------------+----------------+----------------+----------------+
  *
  * operation - XENSND_OP_SET_VOLUME for volume set
@@ -713,9 +774,11 @@ struct xensnd_rw_req {
  * +----------------+----------------+----------------+----------------+
  * |                              length                               | 16
  * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 32
+ * |                             reserved                              | 64
  * +----------------+----------------+----------------+----------------+
  *
  * operation - XENSND_OP_MUTE for mute or XENSND_OP_UNMUTE for unmute
@@ -743,32 +806,213 @@ struct xensnd_rw_req {
  *
  * The 'struct xensnd_rw_req' is also used for XENSND_OP_SET_VOLUME,
  * XENSND_OP_GET_VOLUME, XENSND_OP_MUTE, XENSND_OP_UNMUTE.
+ *
+ * Request stream running state change - trigger PCM stream running state
+ * to start, stop, pause or resume:
+ *
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |   _OP_TRIGGER  |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |      type      |                     reserved                     | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 16
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * type - uint8_t, XENSND_OP_TRIGGER_XXX value
  */
 
+struct xensnd_trigger_req {
+	uint8_t type;
+};
+
 /*
- *---------------------------------- Responses --------------------------------
+ * Request stream parameter ranges: request intervals and
+ *   masks of supported ranges for stream configuration values.
  *
- * All response packets have the same length (32 octets)
+ *   Sound device configuration for a particular stream is a limited subset
+ *   of the multidimensional configuration available on XenStore, e.g.
+ *   once the frame rate has been selected there is a limited supported range
+ *   for sample rates becomes available (which might be the same set configured
+ *   on XenStore or less). For example, selecting 96kHz sample rate may limit
+ *   number of channels available for such configuration from 4 to 2, etc.
+ *   Thus, each call to XENSND_OP_HW_PARAM_QUERY may reduce configuration
+ *   space making it possible to iteratively get the final stream configuration,
+ *   used in XENSND_OP_OPEN request.
+ *
+ *   See response format for this request.
  *
- * Response for all requests:
  *         0                1                 2               3        octet
  * +----------------+----------------+----------------+----------------+
- * |               id                |    operation   |    reserved    | 4
+ * |               id                | _HW_PARAM_QUERY|    reserved    | 4
  * +----------------+----------------+----------------+----------------+
- * |                              status                               | 8
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                     formats mask low 32-bit                       | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                     formats mask high 32-bit                      | 16
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 12
+ * |                              min rate                             | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                              max rate                             | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                            min channels                           | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                            max channels                           | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                         min buffer frames                         | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                         max buffer frames                         | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                         min period frames                         | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                         max period frames                         | 48
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 52
  * +----------------+----------------+----------------+----------------+
  * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
  * +----------------+----------------+----------------+----------------+
- * |                             reserved                              | 32
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * formats - uint64_t, bit mask representing values of the parameter
+ *     made as bitwise OR of (1 << XENSND_PCM_FORMAT_XXX) values
+ *
+ * For interval parameters:
+ *   min - uint32_t, minimum value of the parameter
+ *   max - uint32_t, maximum value of the parameter
+ *
+ * Frame is defined as a product of the number of channels by the
+ * number of octets per one sample.
+ */
+
+struct xensnd_query_hw_param {
+	uint64_t formats;
+	struct {
+		uint32_t min;
+		uint32_t max;
+	} rates;
+	struct {
+		uint32_t min;
+		uint32_t max;
+	} channels;
+	struct {
+		uint32_t min;
+		uint32_t max;
+	} buffer;
+	struct {
+		uint32_t min;
+		uint32_t max;
+	} period;
+};
+
+/*
+ *---------------------------------- Responses --------------------------------
+ *
+ * All response packets have the same length (64 octets)
+ *
+ * All response packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |    operation   |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              status                               | 8
  * +----------------+----------------+----------------+----------------+
  *
  * id - uint16_t, copied from the request
  * operation - uint8_t, XENSND_OP_* - copied from request
  * status - int32_t, response status, zero on success and -XEN_EXX on failure
+ *
+ *
+ * HW parameter query response - response for XENSND_OP_HW_PARAM_QUERY:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |    operation   |    reserved    | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                              status                               | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                     formats mask low 32-bit                       | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                     formats mask high 32-bit                      | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                              min rate                             | 20
+ * +----------------+----------------+----------------+----------------+
+ * |                              max rate                             | 24
+ * +----------------+----------------+----------------+----------------+
+ * |                            min channels                           | 28
+ * +----------------+----------------+----------------+----------------+
+ * |                            max channels                           | 32
+ * +----------------+----------------+----------------+----------------+
+ * |                         min buffer frames                         | 36
+ * +----------------+----------------+----------------+----------------+
+ * |                         max buffer frames                         | 40
+ * +----------------+----------------+----------------+----------------+
+ * |                         min period frames                         | 44
+ * +----------------+----------------+----------------+----------------+
+ * |                         max period frames                         | 48
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 52
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * Meaning of the values in this response is the same as for
+ * XENSND_OP_HW_PARAM_QUERY request.
+ */
+
+/*
+ *----------------------------------- Events ----------------------------------
+ *
+ * Events are sent via shared page allocated by the front and propagated by
+ *   evt-event-channel/evt-ring-ref XenStore entries
+ * All event packets have the same length (64 octets)
+ * All event packets have common header:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |      type      |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ *
+ * id - uint16_t, event id, may be used by front
+ * type - uint8_t, type of the event
+ *
+ *
+ * Current stream position - event from back to front when stream's
+ *   playback/capture position has advanced:
+ *         0                1                 2               3        octet
+ * +----------------+----------------+----------------+----------------+
+ * |               id                |   _EVT_CUR_POS |   reserved     | 4
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 8
+ * +----------------+----------------+----------------+----------------+
+ * |                         position low 32-bit                       | 12
+ * +----------------+----------------+----------------+----------------+
+ * |                         position high 32-bit                      | 16
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 20
+ * +----------------+----------------+----------------+----------------+
+ * |/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/|
+ * +----------------+----------------+----------------+----------------+
+ * |                             reserved                              | 64
+ * +----------------+----------------+----------------+----------------+
+ *
+ * position - current value of stream's playback/capture position, octets
+ *
  */
 
+struct xensnd_cur_pos_evt {
+	uint64_t position;
+};
+
 struct xensnd_req {
 	uint16_t id;
 	uint8_t operation;
@@ -776,7 +1020,9 @@ struct xensnd_req {
 	union {
 		struct xensnd_open_req open;
 		struct xensnd_rw_req rw;
-		uint8_t reserved[24];
+		struct xensnd_trigger_req trigger;
+		struct xensnd_query_hw_param hw_param;
+		uint8_t reserved[56];
 	} op;
 };
 
@@ -785,9 +1031,53 @@ struct xensnd_resp {
 	uint8_t operation;
 	uint8_t reserved;
 	int32_t status;
-	uint8_t reserved1[24];
+	union {
+		struct xensnd_query_hw_param hw_param;
+		uint8_t reserved1[56];
+	} resp;
+};
+
+struct xensnd_evt {
+	uint16_t id;
+	uint8_t type;
+	uint8_t reserved[5];
+	union {
+		struct xensnd_cur_pos_evt cur_pos;
+		uint8_t reserved[56];
+	} op;
 };
 
 DEFINE_RING_TYPES(xen_sndif, struct xensnd_req, struct xensnd_resp);
 
+/*
+ ******************************************************************************
+ *                        Back to front events delivery
+ ******************************************************************************
+ * In order to deliver asynchronous events from back to front a shared page is
+ * allocated by front and its granted reference propagated to back via
+ * XenStore entries (evt-ring-ref/evt-event-channel).
+ * This page has a common header used by both front and back to synchronize
+ * access and control event's ring buffer, while back being a producer of the
+ * events and front being a consumer. The rest of the page after the header
+ * is used for event packets.
+ *
+ * Upon reception of an event(s) front may confirm its reception
+ * for either each event, group of events or none.
+ */
+
+struct xensnd_event_page {
+	uint32_t in_cons;
+	uint32_t in_prod;
+	uint8_t reserved[56];
+};
+
+#define XENSND_EVENT_PAGE_SIZE XEN_PAGE_SIZE
+#define XENSND_IN_RING_OFFS (sizeof(struct xensnd_event_page))
+#define XENSND_IN_RING_SIZE (XENSND_EVENT_PAGE_SIZE - XENSND_IN_RING_OFFS)
+#define XENSND_IN_RING_LEN (XENSND_IN_RING_SIZE / sizeof(struct xensnd_evt))
+#define XENSND_IN_RING(page) \
+	((struct xensnd_evt *)((char *)(page) + XENSND_IN_RING_OFFS))
+#define XENSND_IN_RING_REF(page, idx) \
+	(XENSND_IN_RING((page))[(idx) % XENSND_IN_RING_LEN])
+
 #endif /* __XEN_PUBLIC_IO_SNDIF_H__ */
