Added implementing ALSA volume control

src/main.c

@@ -87,6 +87,7 @@ static const gchar *output = NULL;
 static const gchar *pid_file = NULL;
 static const gchar *log_file = NULL;
 static const gchar *mime_filter = NULL;
+static const gchar *alsa_mixer = NULL;
 
 /* Generic GMediaRender options */
 static GOptionEntry option_entries[] = {
@@ -125,6 +126,8 @@ static GOptionEntry option_entries[] = {
 	  "Dump Rendering Control service description XML and exit.", NULL },
 	{ "dump-transport-scpd", 0, 0, G_OPTION_ARG_NONE, &show_transport_scpd,
 	  "Dump A/V Transport service description XML and exit.", NULL },
+        { "mixer", 0, 0, G_OPTION_ARG_STRING, &alsa_mixer,
+          "ALSA mixer control to use", NULL },
 	{ NULL }
 };
 
@@ -283,7 +286,7 @@ int main(int argc, char **argv)
 		return EXIT_FAILURE;
 	}
 
-	rc = output_init(output);
+	rc = output_init(output, alsa_mixer);
 	if (rc != 0) {
 		Log_error("main",
 			  "ERROR: Failed to initialize Output subsystem");

src/output.c

@@ -52,6 +52,80 @@ static struct output_module *modules[] = {
 #endif
 };
 
+/** Additions: ALSA volume control **/
+
+#include <alsa/asoundlib.h>
+
+snd_mixer_elem_t* 	mixer_elem;
+long			mixer_max;
+snd_mixer_t 		*mixer_handle;
+snd_mixer_selem_id_t 	*mixer_sid;
+
+int init_alsa(const char *mixer_name) {
+	mixer_max = 0;
+    	long min;
+    	const char *card = "default";
+
+	if (! mixer_name) {
+		Log_info("alsa", "No mixer control defined, won't enable ALSA mixer control");
+		return -1;
+	}
+
+    	snd_mixer_open(&mixer_handle, 0);
+
+	if (! mixer_handle) {
+		Log_error("alsa", "Can't open mixer");
+                return -1;
+	}
+
+    	snd_mixer_attach(mixer_handle, card);
+    	snd_mixer_selem_register(mixer_handle, NULL, NULL);
+    	snd_mixer_load(mixer_handle);
+
+    	snd_mixer_selem_id_alloca(&mixer_sid);
+
+	if (! mixer_sid) {
+                Log_error("alsa", "Can't allocate mixer_sid");
+                return -1;
+        }
+
+    	snd_mixer_selem_id_set_index(mixer_sid, 0);
+    	snd_mixer_selem_id_set_name(mixer_sid, mixer_name);
+    	mixer_elem = snd_mixer_find_selem(mixer_handle, mixer_sid);
+
+	if (! mixer_elem) {
+                Log_error("alsa", "Mixer control %s does not exist", mixer_name);
+                return -1;
+        }
+
+	snd_mixer_selem_get_playback_volume_range(mixer_elem, &min, &mixer_max);
+
+	return 0;
+}
+
+void close_alsa(void) {
+	snd_mixer_close(mixer_handle);
+}
+
+int set_alsa_volume(float value) {
+	if (mixer_max <= 0)
+		return 0;
+
+	long volume = value;
+
+	if (!(snd_mixer_selem_set_playback_volume_all(
+                mixer_elem, volume * mixer_max / 100)))
+		return 0;
+	else
+		return 1;
+}
+
+float get_alsa_volume(void) {
+	return -1;
+}
+
+/************************************/
+
 static struct output_module *output_module = NULL;
 
 void output_dump_modules(void)
@@ -72,10 +146,12 @@ void output_dump_modules(void)
 	}
 }
 
-int output_init(const char *shortname)
+int output_init(const char *shortname, const char *alsa_mixer)
 {
 	int count;
 
+	init_alsa(alsa_mixer);
+
 	count = sizeof(modules) / sizeof(struct output_module *);
 	if (count == 0) {
 		Log_error("output", "No output module available");
@@ -194,12 +270,24 @@ int output_get_position(gint64 *track_dur, gint64 *track_pos) {
 }
 
 int output_get_volume(float *value) {
+	/* Try ALSA first */
+	float vol = get_alsa_volume();
+	if (vol >= 0) {
+		return vol;
+	}
+	/* Go on if ALSA volume isn't supported */
 	if (output_module && output_module->get_volume) {
 		return output_module->get_volume(value);
 	}
 	return -1;
 }
 int output_set_volume(float value) {
+	/* Try ALSA first */
+	float vol = set_alsa_volume(value);
+        if (vol >= 0) {
+                return vol;
+        }
+	/* Go on if ALSA volume isn't supported */
 	if (output_module && output_module->set_volume) {
 		return output_module->set_volume(value);
 	}

src/output.h

@@ -39,7 +39,12 @@ typedef void (*output_transition_cb_t)(enum PlayFeedback);
 // callback with changes we send back to the controlling layer.
 typedef void (*output_update_meta_cb_t)(const struct SongMetaData *);
 
-int output_init(const char *shortname);
+int init_alsa(const char *mixer_name);
+void close_alsa(void);
+int set_alsa_volume(float value);
+float get_alsa_volume(void);
+
+int output_init(const char *shortname, const char *alsa_mixer);
 int output_add_options(GOptionContext *ctx);
 void output_dump_modules(void);