alsa-ucm: Disable UCM devices when suspending

This might save some power, according to the discussion here:
https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/294#note_522388

src/modules/alsa/alsa-sink.c

@@ -1049,6 +1049,12 @@ static void suspend(struct userdata *u) {
     pa_sink_set_max_rewind_within_thread(u->sink, 0);
     pa_sink_set_max_request_within_thread(u->sink, 0);
 
+    /* Disabling the UCM devices may save some power. */
+    if (u->ucm_context) {
+        pa_alsa_ucm_port_data *data = PA_DEVICE_PORT_DATA(u->sink->active_port);
+        pa_alsa_ucm_port_enable_devices(data, false);
+    }
+
     pa_log_info("Device suspended...");
 }
 
@@ -1164,6 +1170,13 @@ static int unsuspend(struct userdata *u, bool recovering) {
 
     pa_log_info("Trying resume...");
 
+    /* We disable all UCM devices when suspending, so let's enable them
+     * again. */
+    if (u->ucm_context) {
+        pa_alsa_ucm_port_data *data = PA_DEVICE_PORT_DATA(u->sink->active_port);
+        pa_alsa_ucm_port_enable_devices(data, true);
+    }
+
     if ((is_iec958(u) || is_hdmi(u)) && pa_sink_is_passthrough(u->sink)) {
         /* Need to open device in NONAUDIO mode */
         int len = strlen(u->device_name) + 8;

src/modules/alsa/alsa-source.c

@@ -954,6 +954,12 @@ static void suspend(struct userdata *u) {
     /* Close PCM device */
     close_pcm(u);
 
+    /* Disabling the UCM devices may save some power. */
+    if (u->ucm_context) {
+        pa_alsa_ucm_port_data *data = PA_DEVICE_PORT_DATA(u->source->active_port);
+        pa_alsa_ucm_port_enable_devices(data, false);
+    }
+
     pa_log_info("Device suspended...");
 }
 
@@ -1044,6 +1050,13 @@ static int unsuspend(struct userdata *u, bool recovering) {
 
     pa_log_info("Trying resume...");
 
+    /* We disable all UCM devices when suspending, so let's enable them
+     * again. */
+    if (u->ucm_context) {
+        pa_alsa_ucm_port_data *data = PA_DEVICE_PORT_DATA(u->source->active_port);
+        pa_alsa_ucm_port_enable_devices(data, true);
+    }
+
     if ((err = snd_pcm_open(&u->pcm_handle, u->device_name, SND_PCM_STREAM_CAPTURE,
                             SND_PCM_NONBLOCK|
                             SND_PCM_NO_AUTO_RESAMPLE|

src/modules/alsa/alsa-ucm.c

@@ -2245,6 +2245,29 @@ static void ucm_port_update_available(pa_alsa_ucm_port_data *port) {
     pa_device_port_set_available(port->core_port, available);
 }
 
+void pa_alsa_ucm_port_enable_devices(pa_alsa_ucm_port_data *data, bool enable) {
+    pa_alsa_ucm_device *dev;
+    uint32_t idx;
+
+    pa_assert(data);
+
+    /* first disable then enable */
+    PA_DYNARRAY_FOREACH(dev, data->devices, idx) {
+        int r;
+
+        if (enable) {
+            pa_log_debug("Enabling UCM device %s.", dev->name);
+            if ((r = snd_use_case_set(data->ucm->ucm_mgr, "_enadev", dev->name) < 0))
+                pa_log("Failed to enable UCM device %s: %s", dev->name, pa_cstrerror(r));
+        } else {
+            pa_log_debug("Disabling UCM device %s.", dev->name);
+            if ((r = snd_use_case_set(data->ucm->ucm_mgr, "_disdev", dev->name) < 0))
+                pa_log("Failed to disable UCM device %s: %s", dev->name, pa_cstrerror(r));
+        }
+    }
+}
+
+
 #else /* HAVE_ALSA_UCM */
 
 /* Dummy functions for systems without UCM support */
@@ -2301,4 +2324,7 @@ void pa_alsa_ucm_roled_stream_begin(pa_alsa_ucm_config *ucm, const char *role, p
 void pa_alsa_ucm_roled_stream_end(pa_alsa_ucm_config *ucm, const char *role, pa_direction_t dir) {
 }
 
+void pa_alsa_ucm_port_enable_devices(pa_alsa_ucm_port_data *data, bool enable) {
+}
+
 #endif

src/modules/alsa/alsa-ucm.h

@@ -285,6 +285,8 @@ struct pa_alsa_ucm_port_data {
     int eld_device; /* PCM device number */
 };
 
+void pa_alsa_ucm_port_enable_devices(pa_alsa_ucm_port_data *data, bool enable);
+
 struct pa_alsa_ucm_volume {
     char *mixer_elem;	/* mixer element identifier */
     char *master_elem;	/* master mixer element identifier */