ALSA: xen-front: Implement Xen event channel handling

Handle Xen event channels:
  - create for all configured streams and publish
    corresponding ring references and event channels in Xen store,
    so backend can connect
  - implement event channels interrupt handlers
  - create and destroy event channels with respect to Xen bus state
Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/xen/Makefile

 # SPDX-License-Identifier: GPL-2.0 OR MIT
 
 snd_xen_front-objs := xen_snd_front.o \
-		      xen_snd_front_cfg.o
+		      xen_snd_front_cfg.o \
+		      xen_snd_front_evtchnl.o
 
 obj-$(CONFIG_SND_XEN_FRONTEND) += snd_xen_front.o

sound/xen/xen_snd_front.c

@@ -18,9 +18,11 @@
 #include <xen/interface/io/sndif.h>
 
 #include "xen_snd_front.h"
+#include "xen_snd_front_evtchnl.h"
 
 static void xen_snd_drv_fini(struct xen_snd_front_info *front_info)
 {
+	xen_snd_front_evtchnl_free_all(front_info);
 }
 
 static int sndback_initwait(struct xen_snd_front_info *front_info)
@@ -32,7 +34,12 @@ static int sndback_initwait(struct xen_snd_front_info *front_info)
 	if (ret < 0)
 		return ret;
 
-	return 0;
+	/* create event channels for all streams and publish */
+	ret = xen_snd_front_evtchnl_create_all(front_info, num_streams);
+	if (ret < 0)
+		return ret;
+
+	return xen_snd_front_evtchnl_publish_all(front_info);
 }
 
 static int sndback_connect(struct xen_snd_front_info *front_info)

sound/xen/xen_snd_front.h

@@ -13,9 +13,14 @@
 
 #include "xen_snd_front_cfg.h"
 
+struct xen_snd_front_evtchnl_pair;
+
 struct xen_snd_front_info {
 	struct xenbus_device *xb_dev;
 
+	int num_evt_pairs;
+	struct xen_snd_front_evtchnl_pair *evt_pairs;
+
 	struct xen_front_cfg_card cfg;
 };
 

sound/xen/xen_snd_front_evtchnl.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_EVTCHNL_H
+#define __XEN_SND_FRONT_EVTCHNL_H
+
+#include <xen/interface/io/sndif.h>
+
+struct xen_snd_front_info;
+
+#ifndef GRANT_INVALID_REF
+/*
+ * FIXME: usage of grant reference 0 as invalid grant reference:
+ * grant reference 0 is valid, but never exposed to a PV driver,
+ * because of the fact it is already in use/reserved by the PV console.
+ */
+#define GRANT_INVALID_REF	0
+#endif
+
+/* Timeout in ms to wait for backend to respond. */
+#define VSND_WAIT_BACK_MS	3000
+
+enum xen_snd_front_evtchnl_state {
+	EVTCHNL_STATE_DISCONNECTED,
+	EVTCHNL_STATE_CONNECTED,
+};
+
+enum xen_snd_front_evtchnl_type {
+	EVTCHNL_TYPE_REQ,
+	EVTCHNL_TYPE_EVT,
+};
+
+struct xen_snd_front_evtchnl {
+	struct xen_snd_front_info *front_info;
+	int gref;
+	int port;
+	int irq;
+	int index;
+	/* State of the event channel. */
+	enum xen_snd_front_evtchnl_state state;
+	enum xen_snd_front_evtchnl_type type;
+	/* Either response id or incoming event id. */
+	u16 evt_id;
+	/* Next request id or next expected event id. */
+	u16 evt_next_id;
+	/* Shared ring access lock. */
+	struct mutex ring_io_lock;
+	union {
+		struct {
+			struct xen_sndif_front_ring ring;
+			struct completion completion;
+			/* Serializer for backend IO: request/response. */
+			struct mutex req_io_lock;
+
+			/* Latest response status. */
+			int resp_status;
+			union {
+				struct xensnd_query_hw_param hw_param;
+			} resp;
+		} req;
+		struct {
+			struct xensnd_event_page *page;
+			/* This is needed to handle XENSND_EVT_CUR_POS event. */
+			struct snd_pcm_substream *substream;
+		} evt;
+	} u;
+};
+
+struct xen_snd_front_evtchnl_pair {
+	struct xen_snd_front_evtchnl req;
+	struct xen_snd_front_evtchnl evt;
+};
+
+int xen_snd_front_evtchnl_create_all(struct xen_snd_front_info *front_info,
+				     int num_streams);
+
+void xen_snd_front_evtchnl_free_all(struct xen_snd_front_info *front_info);
+
+int xen_snd_front_evtchnl_publish_all(struct xen_snd_front_info *front_info);
+
+void xen_snd_front_evtchnl_flush(struct xen_snd_front_evtchnl *evtchnl);
+
+void xen_snd_front_evtchnl_pair_set_connected(struct xen_snd_front_evtchnl_pair *evt_pair,
+					      bool is_connected);
+
+void xen_snd_front_evtchnl_pair_clear(struct xen_snd_front_evtchnl_pair *evt_pair);
+
+#endif /* __XEN_SND_FRONT_EVTCHNL_H */