Re: [PATCH v2 8/9] ALSA: virtio: introduce PCM channel map support

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On Sun, 24 Jan 2021, Anton Yakovlev wrote:

Enumerate all available PCM channel maps and create ALSA controls.

Signed-off-by: Anton Yakovlev <anton.yakovlev@xxxxxxxxxxxxxxx>
---
sound/virtio/Makefile       |   1 +
sound/virtio/virtio_card.c  |  15 +++
sound/virtio/virtio_card.h  |   8 ++
sound/virtio/virtio_chmap.c | 237 ++++++++++++++++++++++++++++++++++++
sound/virtio/virtio_pcm.h   |   4 +
5 files changed, 265 insertions(+)
create mode 100644 sound/virtio/virtio_chmap.c

[snip]

diff --git a/sound/virtio/virtio_chmap.c b/sound/virtio/virtio_chmap.c
new file mode 100644
index 000000000000..8a2ddc4dcffb
--- /dev/null
+++ b/sound/virtio/virtio_chmap.c
@@ -0,0 +1,237 @@

[snip]

+/**
+ * virtsnd_chmap_parse_cfg() - Parse the channel map configuration.
+ * @snd: VirtIO sound device.
+ *
+ * This function is called during initial device initialization.
+ *
+ * Context: Any context that permits to sleep.
+ * Return: 0 on success, -errno on failure.
+ */
+int virtsnd_chmap_parse_cfg(struct virtio_snd *snd)
+{
+	struct virtio_device *vdev = snd->vdev;
+	unsigned int i;
+	int rc;
+
+	virtio_cread(vdev, struct virtio_snd_config, chmaps, &snd->nchmaps);
+	if (!snd->nchmaps)
+		return 0;
+
+	snd->chmaps = devm_kcalloc(&vdev->dev, snd->nchmaps,
+				   sizeof(*snd->chmaps), GFP_KERNEL);
+	if (!snd->chmaps)
+		return -ENOMEM;
+
+	rc = virtsnd_ctl_query_info(snd, VIRTIO_SND_R_CHMAP_INFO, 0,
+				    snd->nchmaps, sizeof(*snd->chmaps),
+				    snd->chmaps);
+	if (rc)
+		return rc;
+
+	/* Count the number of channel maps per each PCM device/stream. */
+	for (i = 0; i < snd->nchmaps; ++i) {
+		struct virtio_snd_chmap_info *info = &snd->chmaps[i];
+		unsigned int nid = le32_to_cpu(info->hdr.hda_fn_nid);
+		struct virtio_pcm *pcm;
+		struct virtio_pcm_stream *stream;
+
+		pcm = virtsnd_pcm_find_or_create(snd, nid);
+		if (IS_ERR(pcm))
+			return PTR_ERR(pcm);
+
+		switch (info->direction) {
+		case VIRTIO_SND_D_OUTPUT: {
+			stream = &pcm->streams[SNDRV_PCM_STREAM_PLAYBACK];
+			break;
+		}
+		case VIRTIO_SND_D_INPUT: {
+			stream = &pcm->streams[SNDRV_PCM_STREAM_CAPTURE];
+			break;
+		}
+		default: {
+			dev_err(&vdev->dev,
+				"chmap #%u: unknown direction (%u)\n", i,
+				info->direction);
+			return -EINVAL;
+		}
+		}
+
+		stream->nchmaps++;
+	}
+
+	return 0;
+}
+
+/**
+ * virtsnd_chmap_add_ctls() - Create an ALSA control for channel maps.
+ * @pcm: ALSA PCM device.
+ * @direction: PCM stream direction (SNDRV_PCM_STREAM_XXX).
+ * @stream: VirtIO PCM stream.
+ *
+ * Context: Any context.
+ * Return: 0 on success, -errno on failure.
+ */
+static int virtsnd_chmap_add_ctls(struct snd_pcm *pcm, int direction,
+				  struct virtio_pcm_stream *stream)
+{
+	unsigned int i;
+	int max_channels = 0;
+
+	for (i = 0; i < stream->nchmaps; i++)
+		if (max_channels < stream->chmaps[i].channels)
+			max_channels = stream->chmaps[i].channels;
+
+	return snd_pcm_add_chmap_ctls(pcm, direction, stream->chmaps,
+				      max_channels, 0, NULL);
+}
+
+/**
+ * virtsnd_chmap_build_devs() - Build ALSA controls for channel maps.
+ * @snd: VirtIO sound device.
+ *
+ * Context: Any context.
+ * Return: 0 on success, -errno on failure.
+ */
+int virtsnd_chmap_build_devs(struct virtio_snd *snd)
+{
+	struct virtio_device *vdev = snd->vdev;
+	struct virtio_pcm *pcm;
+	struct virtio_pcm_stream *stream;
+	unsigned int i;
+	int rc;
+
+	/* Allocate channel map elements per each PCM device/stream. */
+	list_for_each_entry(pcm, &snd->pcm_list, list) {
+		for (i = 0; i < ARRAY_SIZE(pcm->streams); ++i) {
+			stream = &pcm->streams[i];
+
+			if (!stream->nchmaps)
+				continue;
+
+			stream->chmaps = devm_kcalloc(&vdev->dev,
+						      stream->nchmaps + 1,
+						      sizeof(*stream->chmaps),
+						      GFP_KERNEL);
+			if (!stream->chmaps)
+				return -ENOMEM;
+
+			stream->nchmaps = 0;
+		}
+	}
+
+	/* Initialize channel maps per each PCM device/stream. */
+	for (i = 0; i < snd->nchmaps; ++i) {
+		struct virtio_snd_chmap_info *info = &snd->chmaps[i];
+		unsigned int nid = le32_to_cpu(info->hdr.hda_fn_nid);
+		unsigned int channels = info->channels;
+		unsigned int ch;
+		struct snd_pcm_chmap_elem *chmap;
+
+		pcm = virtsnd_pcm_find(snd, nid);
+		if (IS_ERR(pcm))
+			return PTR_ERR(pcm);
+
+		if (info->direction == VIRTIO_SND_D_OUTPUT)
+			stream = &pcm->streams[SNDRV_PCM_STREAM_PLAYBACK];
+		else
+			stream = &pcm->streams[SNDRV_PCM_STREAM_CAPTURE];
+
+		chmap = &stream->chmaps[stream->nchmaps++];
+
+		if (channels > ARRAY_SIZE(chmap->map))
+			channels = ARRAY_SIZE(chmap->map);
+
+		chmap->channels = channels;
+
+		for (ch = 0; ch < channels; ++ch) {
+			u8 position = info->positions[ch];
+
+			if (position >= ARRAY_SIZE(g_v2a_position_map))
+				return -EINVAL;
+
+			chmap->map[ch] = g_v2a_position_map[position];
+		}
+	}

You enter this function after virtsnd_chmap_parse_cfg() has run. And virtsnd_chmap_parse_cfg() has already found or created all the PCMs and counted channel maps - the same way as you do in the above loop. Wouldn't it be enough to reuse the result of that counting and avoid re-counting here?

+
+	/* Create an ALSA control per each PCM device/stream. */
+	list_for_each_entry(pcm, &snd->pcm_list, list) {
+		if (!pcm->pcm)
+			continue;
+
+		for (i = 0; i < ARRAY_SIZE(pcm->streams); ++i) {
+			stream = &pcm->streams[i];
+
+			if (!stream->nchmaps)
+				continue;
+
+			rc = virtsnd_chmap_add_ctls(pcm->pcm, i, stream);
+			if (rc)
+				return rc;
+		}
+	}
+
+	return 0;
+}
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