From 8168dfdbc1bca47b7a77f2e1f04425057c767ad5 Mon Sep 17 00:00:00 2001
From: Wim Taymans <wtaymans@redhat.com>
Date: Wed, 1 Jul 2020 12:54:27 +0200
Subject: [PATCH] alsa-pcm: allow setting number of channels

Allow passing the number of channels when creating a device to
restrict the negotiated channels.
---
 spa/include/spa/param/audio/raw.h  | 2 ++
 spa/plugins/alsa/alsa-pcm-sink.c   | 2 ++
 spa/plugins/alsa/alsa-pcm-source.c | 2 ++
 spa/plugins/alsa/alsa-pcm.c        | 7 +++++++
 spa/plugins/alsa/alsa-pcm.h        | 2 ++
 5 files changed, 15 insertions(+)

diff --git a/spa/include/spa/param/audio/raw.h b/spa/include/spa/param/audio/raw.h
index 5f63d8187..18debcce4 100644
--- a/spa/include/spa/param/audio/raw.h
+++ b/spa/include/spa/param/audio/raw.h
@@ -221,6 +221,8 @@ struct spa_audio_info_raw {
 
 #define SPA_KEY_AUDIO_CHANNEL		"audio.channel"		/**< an audio channel as string,
 								  *  Ex. "FL" */
+#define SPA_KEY_AUDIO_CHANNELS		"audio.channels"	/**< an audio channel count as int */
+
 struct spa_audio_info_dsp {
 	enum spa_audio_format format;		/*< format, one of the DSP formats in enum spa_audio_format_dsp */
 };
diff --git a/spa/plugins/alsa/alsa-pcm-sink.c b/spa/plugins/alsa/alsa-pcm-sink.c
index 2766a7042..f6acb3fdc 100644
--- a/spa/plugins/alsa/alsa-pcm-sink.c
+++ b/spa/plugins/alsa/alsa-pcm-sink.c
@@ -751,6 +751,8 @@ impl_init(const struct spa_handle_factory *factory,
 	for (i = 0; info && i < info->n_items; i++) {
 		if (!strcmp(info->items[i].key, SPA_KEY_API_ALSA_PATH)) {
 			snprintf(this->props.device, 63, "%s", info->items[i].value);
+		} else if (!strcmp(info->items[i].key, SPA_KEY_AUDIO_CHANNELS)) {
+			this->default_channels = atoi(info->items[i].value);
 		}
 	}
 
diff --git a/spa/plugins/alsa/alsa-pcm-source.c b/spa/plugins/alsa/alsa-pcm-source.c
index 297fb089f..6bb244e35 100644
--- a/spa/plugins/alsa/alsa-pcm-source.c
+++ b/spa/plugins/alsa/alsa-pcm-source.c
@@ -770,6 +770,8 @@ impl_init(const struct spa_handle_factory *factory,
 	for (i = 0; info && i < info->n_items; i++) {
 		if (!strcmp(info->items[i].key, SPA_KEY_API_ALSA_PATH)) {
 			snprintf(this->props.device, 63, "%s", info->items[i].value);
+		} else if (!strcmp(info->items[i].key, SPA_KEY_AUDIO_CHANNELS)) {
+			this->default_channels = atoi(info->items[i].value);
 		}
 	}
 	return 0;
diff --git a/spa/plugins/alsa/alsa-pcm.c b/spa/plugins/alsa/alsa-pcm.c
index e009f2564..404e0bdfb 100644
--- a/spa/plugins/alsa/alsa-pcm.c
+++ b/spa/plugins/alsa/alsa-pcm.c
@@ -357,6 +357,13 @@ spa_alsa_enum_format(struct state *state, int seq, uint32_t start, uint32_t num,
 	CHECK(snd_pcm_hw_params_get_channels_min(params, &min), "get_channels_min");
 	CHECK(snd_pcm_hw_params_get_channels_max(params, &max), "get_channels_max");
 
+	if (state->default_channels != 0) {
+		if (min < state->default_channels)
+			min = state->default_channels;
+		if (max > state->default_channels)
+			max = state->default_channels;
+	}
+
 	spa_pod_builder_prop(&b, SPA_FORMAT_AUDIO_channels, 0);
 
 	if ((maps = snd_pcm_query_chmaps(hndl)) != NULL) {
diff --git a/spa/plugins/alsa/alsa-pcm.h b/spa/plugins/alsa/alsa-pcm.h
index f8f9cb7bc..e71221fd2 100644
--- a/spa/plugins/alsa/alsa-pcm.h
+++ b/spa/plugins/alsa/alsa-pcm.h
@@ -101,6 +101,8 @@ struct state {
 	bool have_format;
 	struct spa_audio_info current_format;
 
+	unsigned int default_channels;
+
 	snd_pcm_uframes_t buffer_frames;
 	snd_pcm_uframes_t period_frames;
 	snd_pcm_format_t format;