[alsa-devel] [RFC v4 7/8] ASoC: hdmi-codec: Add ELD control

[Philipp Zabel]

ALSA doesn't know about all the different compressed audio formats,
so there is no interface to let userspace enumerate the formats that
are supported by the connected sink. Exporting the raw ELD bytes to
userspace allows an application to select the appropriate audio format
depending on the current capabilities of the connected HDMI sink device.
Usually userspace then just pretends to ALSA that the data is in one of
the raw 16-bit PCM audio formats and relies on the IEC controls to tell
the sink how to interpret the data.

Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
Reviewed-by: Jyri Sarha <jsarha at ti.com>
Tested-by: Jyri Sarha <jsarha at ti.com>
---
Changes since v3:
 - Expanded commit message
 - Add mutex to lock hcp->eld
---
 sound/soc/codecs/hdmi-codec.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/sound/soc/codecs/hdmi-codec.c b/sound/soc/codecs/hdmi-codec.c
index 7d5db11..9c4e65c 100644
--- a/sound/soc/codecs/hdmi-codec.c
+++ b/sound/soc/codecs/hdmi-codec.c
@@ -55,6 +55,42 @@ enum {
 	DAI_ID_SPDIF,
 };
 
+static int hdmi_eld_ctl_info(struct snd_kcontrol *kcontrol,
+			     struct snd_ctl_elem_info *uinfo)
+{
+	struct snd_soc_component *component = snd_kcontrol_chip(kcontrol);
+	struct hdmi_codec_priv *hcp = snd_soc_component_get_drvdata(component);
+
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_BYTES;
+	uinfo->count = sizeof(hcp->eld);
+
+	return 0;
+}
+
+static int hdmi_eld_ctl_get(struct snd_kcontrol *kcontrol,
+			    struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_soc_component *component = snd_kcontrol_chip(kcontrol);
+	struct hdmi_codec_priv *hcp = snd_soc_component_get_drvdata(component);
+
+	mutex_lock(&hcp->eld_lock);
+	memcpy(ucontrol->value.bytes.data, hcp->eld, sizeof(hcp->eld));
+	mutex_unlock(&hcp->eld_lock);
+
+	return 0;
+}
+
+static const struct snd_kcontrol_new hdmi_controls[] = {
+	{
+		.access = SNDRV_CTL_ELEM_ACCESS_READ |
+			  SNDRV_CTL_ELEM_ACCESS_VOLATILE,
+		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
+		.name = "ELD",
+		.info = hdmi_eld_ctl_info,
+		.get = hdmi_eld_ctl_get,
+	},
+};
+
 static void hdmi_codec_abort(struct device *dev)
 {
 	struct hdmi_codec_priv *hcp = dev_get_drvdata(dev);
@@ -326,6 +362,8 @@ static const struct snd_soc_dai_driver hdmi_spdif_dai = {
 };
 
 static struct snd_soc_codec_driver hdmi_codec = {
+	.controls = hdmi_controls,
+	.num_controls = ARRAY_SIZE(hdmi_controls),
 	.dapm_widgets = hdmi_widgets,
 	.num_dapm_widgets = ARRAY_SIZE(hdmi_widgets),
 	.dapm_routes = hdmi_routes,
-- 
2.7.0