alsa: allow override of channel map

spa/plugins/alsa/alsa-pcm-sink.c

@@ -783,9 +783,18 @@ impl_init(const struct spa_handle_factory *factory,
 			this->default_rate = atoi(info->items[i].value);
 		} else if (!strcmp(info->items[i].key, SPA_KEY_AUDIO_FORMAT)) {
 			this->default_format = spa_alsa_format_from_name(info->items[i].value, 128);
+		} else if (!strcmp(info->items[i].key, SPA_KEY_AUDIO_POSITION)) {
+			size_t len;
+			const char *p = info->items[i].value;
+			while (*p && this->default_pos.channels < SPA_AUDIO_MAX_CHANNELS) {
+				if ((len = strcspn(p, ",")) == 0)
+					break;
+				this->default_pos.pos[this->default_pos.channels++] =
+					spa_alsa_channel_from_name(p, len);
+				p += len + strspn(p+len, ",");
+			}
 		}
 	}
-
 	return 0;
 }
 

spa/plugins/alsa/alsa-pcm-source.c

@@ -804,6 +804,16 @@ impl_init(const struct spa_handle_factory *factory,
 			this->default_rate = atoi(info->items[i].value);
 		} else if (!strcmp(info->items[i].key, SPA_KEY_AUDIO_FORMAT)) {
 			this->default_format = spa_alsa_format_from_name(info->items[i].value, 128);
+		} else if (!strcmp(info->items[i].key, SPA_KEY_AUDIO_POSITION)) {
+			size_t len;
+			const char *p = info->items[i].value;
+			while (*p && this->default_pos.channels < SPA_AUDIO_MAX_CHANNELS) {
+				if ((len = strcspn(p, ",")) == 0)
+					break;
+				this->default_pos.pos[this->default_pos.channels++] =
+					spa_alsa_channel_from_name(p, len);
+				p += len + strspn(p+len, ",");
+			}
 		}
 	}
 	return 0;

spa/plugins/alsa/alsa-pcm.c

@@ -198,12 +198,7 @@ static const struct def_mask default_layouts[] = {
 
 #define _C(ch)	(SPA_AUDIO_CHANNEL_ ##ch)
 
-struct def_map {
+static const struct channel_map default_map[] = {
-	uint32_t channels;
-	uint32_t pos[SPA_AUDIO_MAX_CHANNELS];
-};
-
-static const struct def_map default_map[] = {
 	{ 0, { 0, } } ,
 	{ 1, { _C(MONO), } },
 	{ 2, { _C(FL), _C(FR), } },
@@ -417,6 +412,8 @@ skip_channels:
 		snd_pcm_free_chmaps(maps);
 	}
 	else {
+		const struct channel_map *map = NULL;
+
 		if (result.index > 0)
 			goto enum_end;
 
@@ -430,8 +427,13 @@ skip_channels:
 		}
 		spa_pod_builder_pop(&b, &f[1]);
 
-		if (min == max && min <= 8) {
+		if (min == max) {
-			const struct def_map *map = &default_map[min];
+			if (state->default_pos.channels == min)
+				map = &state->default_pos;
+			else if (min == max && min <= 8)
+				map = &default_map[min];
+		}
+		if (map) {
 			spa_pod_builder_prop(&b, SPA_FORMAT_AUDIO_position, 0);
 			spa_pod_builder_push_array(&b, &f[1]);
 			for (j = 0; j < map->channels; j++) {

spa/plugins/alsa/alsa-pcm.h

@@ -80,6 +80,10 @@ struct buffer {
 #define BW_MIN		0.016
 #define BW_PERIOD	(3 * SPA_NSEC_PER_SEC)
 
+struct channel_map {
+	uint32_t channels;
+	uint32_t pos[SPA_AUDIO_MAX_CHANNELS];
+};
 struct state {
 	struct spa_handle handle;
 	struct spa_node node;
@@ -109,6 +113,7 @@ struct state {
 	uint32_t default_format;
 	unsigned int default_channels;
 	unsigned int default_rate;
+	struct channel_map default_pos;
 
 	snd_pcm_uframes_t buffer_frames;
 	snd_pcm_uframes_t period_frames;
@@ -195,6 +200,16 @@ static inline uint32_t spa_alsa_format_from_name(const char *name, size_t len)
 	return SPA_AUDIO_FORMAT_UNKNOWN;
 }
 
+static inline uint32_t spa_alsa_channel_from_name(const char *name, size_t len)
+{
+	int i;
+	for (i = 0; spa_type_audio_channel[i].name; i++) {
+		if (strncmp(name, spa_debug_type_short_name(spa_type_audio_channel[i].name), len) == 0)
+			return spa_type_audio_channel[i].type;
+	}
+	return SPA_AUDIO_CHANNEL_UNKNOWN;
+}
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif