vc4: Report channel mapping back to userspace

raspberrypi inclusion
category: feature
bugzilla: 50432

--------------------------------

This follows logic in hdmi-codec.c to use speaker layout
from ELD to choose a suitable speaker mapping based on
number of channels requested and signal that in audio
infoframe  and report this back to userspace.

This allows apps like speaker-test and kodi to get the
output to the right speakers.
Signed-off-by: NDom Cobley <popcornmix@gmail.com>
Signed-off-by: NFang Yafen <yafen@iscas.ac.cn>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/gpu/drm/vc4/vc4_hdmi.c

@@ -49,6 +49,7 @@
 #include <sound/pcm_drm_eld.h>
 #include <sound/pcm_params.h>
 #include <sound/soc.h>
+#include <sound/tlv.h>
 #include "media/cec.h"
 #include "vc4_drv.h"
 #include "vc4_hdmi.h"
@@ -87,6 +88,311 @@
 /* Fixed HVS4 HSM clock rate */
 #define VC4_HSM_CLOCK 163682864
 
+#define HDMI_CODEC_CHMAP_IDX_UNKNOWN  -1
+
+/*
+ * CEA speaker placement for HDMI 1.4:
+ *
+ *  FL  FLC   FC   FRC   FR   FRW
+ *
+ *                                  LFE
+ *
+ *  RL  RLC   RC   RRC   RR
+ *
+ *  Speaker placement has to be extended to support HDMI 2.0
+ */
+enum hdmi_codec_cea_spk_placement {
+	FL  = BIT(0),	/* Front Left           */
+	FC  = BIT(1),	/* Front Center         */
+	FR  = BIT(2),	/* Front Right          */
+	FLC = BIT(3),	/* Front Left Center    */
+	FRC = BIT(4),	/* Front Right Center   */
+	RL  = BIT(5),	/* Rear Left            */
+	RC  = BIT(6),	/* Rear Center          */
+	RR  = BIT(7),	/* Rear Right           */
+	RLC = BIT(8),	/* Rear Left Center     */
+	RRC = BIT(9),	/* Rear Right Center    */
+	LFE = BIT(10),	/* Low Frequency Effect */
+};
+
+/*
+ * cea Speaker allocation structure
+ */
+struct hdmi_codec_cea_spk_alloc {
+	const int ca_id;
+	unsigned int n_ch;
+	unsigned long mask;
+};
+
+/* Channel maps  stereo HDMI */
+static const struct snd_pcm_chmap_elem hdmi_codec_stereo_chmaps[] = {
+	{ .channels = 2,
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR } },
+	{ }
+};
+
+/* Channel maps for multi-channel playbacks, up to 8 n_ch */
+static const struct snd_pcm_chmap_elem hdmi_codec_8ch_chmaps[] = {
+	{ .channels = 2, /* CA_ID 0x00 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR } },
+	{ .channels = 4, /* CA_ID 0x01 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA } },
+	{ .channels = 4, /* CA_ID 0x02 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC } },
+	{ .channels = 4, /* CA_ID 0x03 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC } },
+	{ .channels = 6, /* CA_ID 0x04 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 6, /* CA_ID 0x05 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 6, /* CA_ID 0x06 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 6, /* CA_ID 0x07 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 6, /* CA_ID 0x08 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR } },
+	{ .channels = 6, /* CA_ID 0x09 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR } },
+	{ .channels = 6, /* CA_ID 0x0A */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR } },
+	{ .channels = 6, /* CA_ID 0x0B */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR } },
+	{ .channels = 8, /* CA_ID 0x0C */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 8, /* CA_ID 0x0D */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 8, /* CA_ID 0x0E */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 8, /* CA_ID 0x0F */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RC, SNDRV_CHMAP_NA } },
+	{ .channels = 8, /* CA_ID 0x10 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RLC, SNDRV_CHMAP_RRC } },
+	{ .channels = 8, /* CA_ID 0x11 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RLC, SNDRV_CHMAP_RRC } },
+	{ .channels = 8, /* CA_ID 0x12 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RLC, SNDRV_CHMAP_RRC } },
+	{ .channels = 8, /* CA_ID 0x13 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_RL, SNDRV_CHMAP_RR,
+		   SNDRV_CHMAP_RLC, SNDRV_CHMAP_RRC } },
+	{ .channels = 8, /* CA_ID 0x14 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x15 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x16 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x17 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x18 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x19 */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x1A */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x1B */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x1C */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x1D */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_NA, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x1E */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ .channels = 8, /* CA_ID 0x1F */
+	  .map = { SNDRV_CHMAP_FL, SNDRV_CHMAP_FR, SNDRV_CHMAP_LFE,
+		   SNDRV_CHMAP_FC, SNDRV_CHMAP_NA, SNDRV_CHMAP_NA,
+		   SNDRV_CHMAP_FLC, SNDRV_CHMAP_FRC } },
+	{ }
+};
+
+/*
+ * hdmi_codec_channel_alloc: speaker configuration available for CEA
+ *
+ * This is an ordered list that must match with hdmi_codec_8ch_chmaps struct
+ * The preceding ones have better chances to be selected by
+ * hdmi_codec_get_ch_alloc_table_idx().
+ */
+static const struct hdmi_codec_cea_spk_alloc hdmi_codec_channel_alloc[] = {
+	{ .ca_id = 0x00, .n_ch = 2,
+	  .mask = FL | FR},
+	/* 2.1 */
+	{ .ca_id = 0x01, .n_ch = 4,
+	  .mask = FL | FR | LFE},
+	/* Dolby Surround */
+	{ .ca_id = 0x02, .n_ch = 4,
+	  .mask = FL | FR | FC },
+	/* surround51 */
+	{ .ca_id = 0x0b, .n_ch = 6,
+	  .mask = FL | FR | LFE | FC | RL | RR},
+	/* surround40 */
+	{ .ca_id = 0x08, .n_ch = 6,
+	  .mask = FL | FR | RL | RR },
+	/* surround41 */
+	{ .ca_id = 0x09, .n_ch = 6,
+	  .mask = FL | FR | LFE | RL | RR },
+	/* surround50 */
+	{ .ca_id = 0x0a, .n_ch = 6,
+	  .mask = FL | FR | FC | RL | RR },
+	/* 6.1 */
+	{ .ca_id = 0x0f, .n_ch = 8,
+	  .mask = FL | FR | LFE | FC | RL | RR | RC },
+	/* surround71 */
+	{ .ca_id = 0x13, .n_ch = 8,
+	  .mask = FL | FR | LFE | FC | RL | RR | RLC | RRC },
+	/* others */
+	{ .ca_id = 0x03, .n_ch = 8,
+	  .mask = FL | FR | LFE | FC },
+	{ .ca_id = 0x04, .n_ch = 8,
+	  .mask = FL | FR | RC},
+	{ .ca_id = 0x05, .n_ch = 8,
+	  .mask = FL | FR | LFE | RC },
+	{ .ca_id = 0x06, .n_ch = 8,
+	  .mask = FL | FR | FC | RC },
+	{ .ca_id = 0x07, .n_ch = 8,
+	  .mask = FL | FR | LFE | FC | RC },
+	{ .ca_id = 0x0c, .n_ch = 8,
+	  .mask = FL | FR | RC | RL | RR },
+	{ .ca_id = 0x0d, .n_ch = 8,
+	  .mask = FL | FR | LFE | RL | RR | RC },
+	{ .ca_id = 0x0e, .n_ch = 8,
+	  .mask = FL | FR | FC | RL | RR | RC },
+	{ .ca_id = 0x10, .n_ch = 8,
+	  .mask = FL | FR | RL | RR | RLC | RRC },
+	{ .ca_id = 0x11, .n_ch = 8,
+	  .mask = FL | FR | LFE | RL | RR | RLC | RRC },
+	{ .ca_id = 0x12, .n_ch = 8,
+	  .mask = FL | FR | FC | RL | RR | RLC | RRC },
+	{ .ca_id = 0x14, .n_ch = 8,
+	  .mask = FL | FR | FLC | FRC },
+	{ .ca_id = 0x15, .n_ch = 8,
+	  .mask = FL | FR | LFE | FLC | FRC },
+	{ .ca_id = 0x16, .n_ch = 8,
+	  .mask = FL | FR | FC | FLC | FRC },
+	{ .ca_id = 0x17, .n_ch = 8,
+	  .mask = FL | FR | LFE | FC | FLC | FRC },
+	{ .ca_id = 0x18, .n_ch = 8,
+	  .mask = FL | FR | RC | FLC | FRC },
+	{ .ca_id = 0x19, .n_ch = 8,
+	  .mask = FL | FR | LFE | RC | FLC | FRC },
+	{ .ca_id = 0x1a, .n_ch = 8,
+	  .mask = FL | FR | RC | FC | FLC | FRC },
+	{ .ca_id = 0x1b, .n_ch = 8,
+	  .mask = FL | FR | LFE | RC | FC | FLC | FRC },
+	{ .ca_id = 0x1c, .n_ch = 8,
+	  .mask = FL | FR | RL | RR | FLC | FRC },
+	{ .ca_id = 0x1d, .n_ch = 8,
+	  .mask = FL | FR | LFE | RL | RR | FLC | FRC },
+	{ .ca_id = 0x1e, .n_ch = 8,
+	  .mask = FL | FR | FC | RL | RR | FLC | FRC },
+	{ .ca_id = 0x1f, .n_ch = 8,
+	  .mask = FL | FR | LFE | FC | RL | RR | FLC | FRC },
+};
+
+static unsigned long hdmi_codec_spk_mask_from_alloc(int spk_alloc)
+{
+	int i;
+	static const unsigned long hdmi_codec_eld_spk_alloc_bits[] = {
+		[0] = FL | FR, [1] = LFE, [2] = FC, [3] = RL | RR,
+		[4] = RC, [5] = FLC | FRC, [6] = RLC | RRC,
+	};
+	unsigned long spk_mask = 0;
+
+	for (i = 0; i < ARRAY_SIZE(hdmi_codec_eld_spk_alloc_bits); i++) {
+		if (spk_alloc & (1 << i))
+			spk_mask |= hdmi_codec_eld_spk_alloc_bits[i];
+	}
+
+	return spk_mask;
+}
+
+static int hdmi_codec_get_ch_alloc_table_idx(struct vc4_hdmi *vc4_hdmi,
+					     unsigned char channels)
+{
+	struct drm_connector *connector = &vc4_hdmi->connector;
+	int i;
+	u8 spk_alloc;
+	unsigned long spk_mask;
+	const struct hdmi_codec_cea_spk_alloc *cap = hdmi_codec_channel_alloc;
+
+	spk_alloc = drm_eld_get_spk_alloc(connector->eld);
+	spk_mask = hdmi_codec_spk_mask_from_alloc(spk_alloc);
+
+	for (i = 0; i < ARRAY_SIZE(hdmi_codec_channel_alloc); i++, cap++) {
+		/* If spk_alloc == 0, HDMI is unplugged return stereo config*/
+		if (!spk_alloc && cap->ca_id == 0)
+			return i;
+		if (cap->n_ch != channels)
+			continue;
+		if (!(cap->mask == (spk_mask & cap->mask)))
+			continue;
+		return i;
+	}
+
+	return -EINVAL;
+}
+
+static void hdmi_codec_eld_chmap(struct vc4_hdmi *vc4_hdmi)
+{
+	struct drm_connector *connector = &vc4_hdmi->connector;
+	u8 spk_alloc;
+	unsigned long spk_mask;
+
+	spk_alloc = drm_eld_get_spk_alloc(connector->eld);
+	spk_mask = hdmi_codec_spk_mask_from_alloc(spk_alloc);
+
+	/* Detect if only stereo supported, else return 8 channels mappings */
+	if ((spk_mask & ~(FL | FR)))
+		vc4_hdmi->audio.chmap = hdmi_codec_8ch_chmaps;
+	else
+		vc4_hdmi->audio.chmap = hdmi_codec_stereo_chmaps;
+}
+
 static int vc4_hdmi_debugfs_regs(struct seq_file *m, void *unused)
 {
 	struct drm_info_node *node = (struct drm_info_node *)m->private;
@@ -345,6 +651,9 @@ static void vc4_hdmi_set_audio_infoframe(struct drm_encoder *encoder)
 	frame.audio.sample_size = HDMI_AUDIO_SAMPLE_SIZE_STREAM;
 	frame.audio.channels = vc4_hdmi->audio.channels;
 
+	/* Select a channel allocation that matches with ELD and pcm channels */
+	frame.audio.channel_allocation = vc4_hdmi->audio.chmap_idx;
+
 	vc4_hdmi_write_infoframe(encoder, &frame);
 }
 
@@ -943,6 +1252,10 @@ static int vc4_hdmi_audio_startup(struct snd_pcm_substream *substream,
 	if (ret)
 		return ret;
 
+	/* Select chmap supported */
+	vc4_hdmi->audio.max_channels = 8;
+	hdmi_codec_eld_chmap(vc4_hdmi);
+
 	return 0;
 }
 
@@ -1029,6 +1342,7 @@ static int vc4_hdmi_audio_prepare(struct snd_pcm_substream *substream,
 	u32 channel_map;
 	u32 mai_audio_format;
 	u32 mai_sample_rate;
+	int idx;
 
 	if (substream != vc4_hdmi->audio.substream)
 		return -EINVAL;
@@ -1091,6 +1405,14 @@ static int vc4_hdmi_audio_prepare(struct snd_pcm_substream *substream,
 	HDMI_WRITE(HDMI_AUDIO_PACKET_CONFIG, audio_packet_config);
 	vc4_hdmi_set_n_cts(vc4_hdmi);
 
+	idx = hdmi_codec_get_ch_alloc_table_idx(vc4_hdmi, vc4_hdmi->audio.channels);
+	if (idx < 0) {
+		DRM_ERROR("Not able to map channels to speakers (%d)\n", idx);
+		vc4_hdmi->audio.chmap_idx = HDMI_CODEC_CHMAP_IDX_UNKNOWN;
+	} else {
+		vc4_hdmi->audio.chmap_idx = hdmi_codec_channel_alloc[idx].ca_id;
+	}
+
 	vc4_hdmi_set_audio_infoframe(encoder);
 
 	return 0;
@@ -1209,6 +1531,89 @@ static int vc4_spdif_mask_get(struct snd_kcontrol *kcontrol,
 	return 0;
 }
 
+/*
+ * ALSA API channel-map control callbacks
+ */
+static int vc4_chmap_ctl_info(struct snd_kcontrol *kcontrol,
+			      struct snd_ctl_elem_info *uinfo)
+{
+	struct snd_soc_component *component = snd_kcontrol_chip(kcontrol);
+	struct vc4_hdmi *vc4_hdmi = snd_component_to_hdmi(component);
+
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = vc4_hdmi->audio.max_channels;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = SNDRV_CHMAP_LAST;
+
+	return 0;
+}
+
+static int vc4_chmap_ctl_get(struct snd_kcontrol *kcontrol,
+			     struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_soc_component *component = snd_kcontrol_chip(kcontrol);
+	struct vc4_hdmi *vc4_hdmi = snd_component_to_hdmi(component);
+	unsigned const char *map;
+	unsigned int i;
+
+	if (!vc4_hdmi->audio.chmap)
+		return -EINVAL;
+
+	map = vc4_hdmi->audio.chmap[vc4_hdmi->audio.chmap_idx].map;
+
+	for (i = 0; i < vc4_hdmi->audio.max_channels; i++) {
+		if (vc4_hdmi->audio.chmap_idx == HDMI_CODEC_CHMAP_IDX_UNKNOWN)
+			ucontrol->value.integer.value[i] = 0;
+		else
+			ucontrol->value.integer.value[i] = map[i];
+	}
+	return 0;
+}
+
+static int vc4_chmap_ctl_tlv(struct snd_kcontrol *kcontrol, int op_flag,
+			     unsigned int size, unsigned int __user *tlv)
+{
+	struct snd_soc_component *component = snd_kcontrol_chip(kcontrol);
+	struct vc4_hdmi *vc4_hdmi = snd_component_to_hdmi(component);
+	const struct snd_pcm_chmap_elem *map;
+	unsigned int __user *dst;
+	int c, count = 0;
+
+	if (!vc4_hdmi->audio.chmap)
+		return -EINVAL;
+	if (size < 8)
+		return -ENOMEM;
+	if (put_user(SNDRV_CTL_TLVT_CONTAINER, tlv))
+		return -EFAULT;
+	size -= 8;
+	dst = tlv + 2;
+	for (map = vc4_hdmi->audio.chmap; map->channels; map++) {
+		int chs_bytes = map->channels * 4;
+		//if (!valid_chmap_channels(info, map->channels))
+		//	continue;
+		if (size < 8)
+			return -ENOMEM;
+		if (put_user(SNDRV_CTL_TLVT_CHMAP_FIXED, dst) ||
+		    put_user(chs_bytes, dst + 1))
+			return -EFAULT;
+		dst += 2;
+		size -= 8;
+		count += 8;
+		if (size < chs_bytes)
+			return -ENOMEM;
+		size -= chs_bytes;
+		count += chs_bytes;
+		for (c = 0; c < map->channels; c++) {
+			if (put_user(map->map[c], dst))
+				return -EFAULT;
+			dst++;
+		}
+	}
+	if (put_user(count, tlv + 1))
+		return -EFAULT;
+	return 0;
+}
+
 static const struct snd_kcontrol_new vc4_hdmi_audio_controls[] = {
 	{
 		.access = SNDRV_CTL_ELEM_ACCESS_READ |
@@ -1231,6 +1636,16 @@ static const struct snd_kcontrol_new vc4_hdmi_audio_controls[] = {
 		.info =    vc4_spdif_info,
 		.get =     vc4_spdif_mask_get,
 	},
+	{
+		.access = SNDRV_CTL_ELEM_ACCESS_READ |
+			SNDRV_CTL_ELEM_ACCESS_TLV_READ |
+			SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK,
+		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
+		.name = "Playback Channel Map",
+		.info = vc4_chmap_ctl_info,
+		.get = vc4_chmap_ctl_get,
+		.tlv.c = vc4_chmap_ctl_tlv,
+	},
 };
 
 static const struct snd_soc_dapm_widget vc4_hdmi_audio_widgets[] = {

drivers/gpu/drm/vc4/vc4_hdmi.h

@@ -118,6 +118,9 @@ struct vc4_hdmi_audio {
 	bool streaming;
 
 	unsigned char iec_status[4];
+	const struct snd_pcm_chmap_elem *chmap;
+	unsigned int chmap_idx;
+	unsigned int max_channels;
 };
 
 /* General HDMI hardware state. */