bluez5: handle BAP presentation delay and transport latency

For BAP server audio sink, set buffering target so that we try to match
the target presentation delay.  Also adjust requested node latency to be
smaller than the delay.

Also fix BAP transport presentation delay value parsing, and parse also
the other BAP transport properties. Of these, transport latency value
needs to be taken into account in the total sink latency.

spa/plugins/bluez5/media-source.c

@@ -124,6 +124,8 @@ struct impl {
 	unsigned int is_duplex:1;
 	unsigned int use_duplex_source:1;
 
+	unsigned int node_latency;
+
 	int fd;
 	struct spa_source source;
 
@@ -300,6 +302,31 @@ static int impl_node_set_io(void *object, uint32_t id, void *data, size_t size)
 
 static void emit_node_info(struct impl *this, bool full);
 
+static void set_latency(struct impl *this, bool emit_latency)
+{
+	if (this->codec->bap && !this->is_input && this->transport &&
+			this->transport->delay_us != SPA_BT_UNKNOWN_DELAY) {
+		unsigned int node_latency = 2048;
+		unsigned int target = this->transport->delay_us*48000ll/SPA_USEC_PER_SEC * 1/2;
+
+		/* Adjust requested node latency to be somewhat (~1/2) smaller
+		 * than presentation delay. The difference functions as room
+		 * for buffering rate control.
+		 */
+		while (node_latency > 64 && node_latency > target)
+			node_latency /= 2;
+
+		if (this->node_latency != node_latency) {
+			this->node_latency = node_latency;
+			if (emit_latency)
+				emit_node_info(this, false);
+		}
+
+		spa_log_info(this->log, "BAP presentation delay %d us, node latency %u/48000",
+				(int)this->transport->delay_us, node_latency);
+	}
+}
+
 static int apply_props(struct impl *this, const struct spa_pod *param)
 {
 	struct props new_props = this->props;
@@ -851,16 +878,19 @@ static int impl_node_send_command(void *object, const struct spa_command *comman
 static void emit_node_info(struct impl *this, bool full)
 {
 	uint64_t old = full ? this->info.change_mask : 0;
+	char latency[64];
 
 	struct spa_dict_item node_info_items[] = {
 		{ SPA_KEY_DEVICE_API, "bluez5" },
 		{ SPA_KEY_MEDIA_CLASS, this->is_input ? "Audio/Source" : "Stream/Output/Audio" },
-		{ SPA_KEY_NODE_LATENCY, this->is_input ? "" : "512/48000" },
+		{ SPA_KEY_NODE_LATENCY, this->is_input ? "" : latency },
 		{ "media.name", ((this->transport && this->transport->device->name) ?
 					this->transport->device->name : this->codec->bap ? "BAP" : "A2DP") },
 		{ SPA_KEY_NODE_DRIVER, this->is_input ? "true" : "false" },
 	};
 
+	spa_scnprintf(latency, sizeof(latency), "%d/48000", this->node_latency);
+
 	if (full)
 		this->info.change_mask = this->info_all;
 	if (this->info.change_mask) {
@@ -1297,6 +1327,48 @@ static uint32_t get_samples(struct impl *this, uint32_t *duration)
 	return samples;
 }
 
+static void update_target_latency(struct impl *this)
+{
+	struct port *port = &this->port;
+	uint32_t samples, duration;
+
+	if (this->transport == NULL || !port->have_format)
+		return;
+
+	if (!this->codec->bap || this->is_input ||
+			this->transport->delay_us == SPA_BT_UNKNOWN_DELAY)
+		return;
+
+	get_samples(this, &duration);
+
+	/* Presentation delay for BAP server
+	 *
+	 * This assumes the time when we receive the packet is (on average)
+	 * the SDU synchronization reference (see Core v5.3 Vol 6/G Sec 3.2.2 Fig. 3.2,
+	 * BAP v1.0 Sec 7.1.1).
+	 *
+	 * XXX: This is not exactly true, there might be some latency in between,
+	 * XXX: but currently kernel does not provide us any better information.
+	 * XXX: Some controllers (e.g. Intel AX210) also do not seem to set timestamps
+	 * XXX: to the HCI ISO data packets, so it's not clear what we can do here
+	 * XXX: better.
+	 */
+	samples = (uint64_t)this->transport->delay_us *
+		port->current_format.info.raw.rate / SPA_USEC_PER_SEC;
+
+	if (samples > duration)
+		samples -= duration;
+	else
+		samples = 1;
+
+	/* Too small target latency might not produce working audio.
+	 * The minimum (Presentation_Delay_Min) is configured in endpoint
+	 * DBus properties, with some default value on BlueZ side if unspecified.
+	 */
+
+	spa_bt_decode_buffer_set_target_latency(&port->buffer, samples);
+}
+
 static void process_buffering(struct impl *this)
 {
 	struct port *port = &this->port;
@@ -1305,6 +1377,8 @@ static void process_buffering(struct impl *this)
 	uint32_t avail;
 	void *buf;
 
+	update_target_latency(this);
+
 	spa_bt_decode_buffer_process(&port->buffer, samples, duration);
 
 	setup_matching(this);
@@ -1441,6 +1515,14 @@ static const struct spa_node_methods impl_node = {
 	.process = impl_node_process,
 };
 
+static void transport_delay_changed(void *data)
+{
+	struct impl *this = data;
+
+	spa_log_debug(this->log, "transport %p delay changed", this->transport);
+	set_latency(this, true);
+}
+
 static int do_transport_destroy(struct spa_loop *loop,
 				bool async,
 				uint32_t seq,
@@ -1463,6 +1545,7 @@ static void transport_destroy(void *data)
 
 static const struct spa_bt_transport_events transport_events = {
 	SPA_VERSION_BT_TRANSPORT_EVENTS,
+	.delay_changed = transport_delay_changed,
         .destroy = transport_destroy,
 };
 
@@ -1644,6 +1727,10 @@ impl_init(const struct spa_handle_factory *factory,
 		this->duplex_timerfd = -1;
 	}
 
+	this->node_latency = 512;
+
+	set_latency(this, false);
+
 	this->fd = -1;
 
 	return 0;