libpulseaudio: support suspend on idle

Turns out it's pretty easy to implement. Now the buffer queue will
stop requesting for data once the sink is suspended on idle. No
more power wasted.

Note that it is natural that there would be a bit of extra delay
when resume playback after the sink is suspended. In case it is
wanted to be avoided, make sure the module-suspend-on-idle is not
loaded.

packages/libpulseaudio/module-sles-sink.c

@@ -261,6 +261,20 @@ finish:
     pa_log_debug("Thread shutting down");
 }
 
+static int state_func(pa_sink *s, pa_sink_state_t state, pa_suspend_cause_t suspend_cause) {
+    struct userdata *u = s->userdata;
+    int r = 0;
+
+    if (PA_SINK_IS_OPENED(s->state) && state == PA_SINK_SUSPENDED) {
+        r = (*u->bqPlayerPlay)->SetPlayState(u->bqPlayerPlay, SL_PLAYSTATE_STOPPED);
+        //pa_log_debug("Suspended on idle\n");
+    } else if (s->state == PA_SINK_SUSPENDED && PA_SINK_IS_OPENED(state)) {
+        r = (*u->bqPlayerPlay)->SetPlayState(u->bqPlayerPlay, SL_PLAYSTATE_PLAYING);
+        //pa_log_debug("Resume from suspension\n");
+    }
+    return r;
+}
+
 int pa__init(pa_module*m) {
     struct userdata *u = NULL;
     pa_sample_spec ss;
@@ -320,6 +334,7 @@ int pa__init(pa_module*m) {
     }
 
     u->sink->parent.process_msg = pa_sink_process_msg;
+    u->sink->set_state_in_main_thread = state_func;
     u->sink->userdata = u;
 
     pa_sink_set_asyncmsgq(u->sink, u->thread_mq.inq);