[alsa-devel] [PATCH] ASoC: dmic: Add optional wakeup delay

[Matthias Kaehlcke]

On some systems a delay is needed after switching on the clocks, to allow
the DMIC output to stabilize and avoid a popping noise at the beginning
of the recording. Add the optional device tree property 'wakeup-delay-ms'
and apply the specified delay in the new dmic_daiops_prepare().

Signed-off-by: Matthias Kaehlcke <mka at chromium.org>
---
 .../devicetree/bindings/sound/dmic.txt        |  2 +
 sound/soc/codecs/dmic.c                       | 54 ++++++++++++++-----
 2 files changed, 42 insertions(+), 14 deletions(-)

diff --git a/Documentation/devicetree/bindings/sound/dmic.txt b/Documentation/devicetree/bindings/sound/dmic.txt
index 54c8ef6498a8..de741c6609d0 100644
--- a/Documentation/devicetree/bindings/sound/dmic.txt
+++ b/Documentation/devicetree/bindings/sound/dmic.txt
@@ -7,10 +7,12 @@ Required properties:
 
 Optional properties:
 	- dmicen-gpios: GPIO specifier for dmic to control start and stop
+	- wakeup-delay-ms: Delay (in ms) after enabling the DMIC
 
 Example node:
 
 	dmic_codec: dmic at 0 {
 		compatible = "dmic-codec";
 		dmicen-gpios = <&gpio4 3 GPIO_ACTIVE_HIGH>;
+		wakeup-delay-ms <50>;
 	};
diff --git a/sound/soc/codecs/dmic.c b/sound/soc/codecs/dmic.c
index b88a1ee66f80..11f6abf11074 100644
--- a/sound/soc/codecs/dmic.c
+++ b/sound/soc/codecs/dmic.c
@@ -19,6 +19,7 @@
  *
  */
 
+#include <linux/delay.h>
 #include <linux/gpio.h>
 #include <linux/gpio/consumer.h>
 #include <linux/platform_device.h>
@@ -29,24 +30,38 @@
 #include <sound/soc.h>
 #include <sound/soc-dapm.h>
 
+struct dmic {
+	struct gpio_desc *gpio_en;
+	int wakeup_delay;
+};
+
+static int dmic_daiops_prepare(struct snd_pcm_substream *substream,
+				struct snd_soc_dai *dai)
+{
+	struct dmic *dmic = snd_soc_dai_get_drvdata(dai);
+
+	if (dmic->gpio_en)
+		gpiod_set_value(dmic->gpio_en, 1);
+
+	if (dmic->wakeup_delay)
+		msleep(dmic->wakeup_delay);
+
+	return 0;
+}
+
 static int dmic_daiops_trigger(struct snd_pcm_substream *substream,
 		int cmd, struct snd_soc_dai *dai)
 {
-	struct gpio_desc *dmic_en = snd_soc_dai_get_drvdata(dai);
+	struct dmic *dmic = snd_soc_dai_get_drvdata(dai);
 
-	if (!dmic_en)
+	if (!dmic->gpio_en)
 		return 0;
 
 	switch (cmd) {
-	case SNDRV_PCM_TRIGGER_START:
-	case SNDRV_PCM_TRIGGER_RESUME:
-	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
-		gpiod_set_value(dmic_en, 1);
-		break;
 	case SNDRV_PCM_TRIGGER_STOP:
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
-		gpiod_set_value(dmic_en, 0);
+		gpiod_set_value(dmic->gpio_en, 0);
 		break;
 	}
 
@@ -54,6 +69,7 @@ static int dmic_daiops_trigger(struct snd_pcm_substream *substream,
 }
 
 static const struct snd_soc_dai_ops dmic_dai_ops = {
+	.prepare	= dmic_daiops_prepare,
 	.trigger	= dmic_daiops_trigger,
 };
 
@@ -73,14 +89,24 @@ static struct snd_soc_dai_driver dmic_dai = {
 
 static int dmic_codec_probe(struct snd_soc_codec *codec)
 {
-	struct gpio_desc *dmic_en;
+	struct dmic *dmic;
+	int err;
+
+	dmic = devm_kzalloc(codec->dev, sizeof(*dmic), GFP_KERNEL);
+	if (!dmic)
+		return -ENOMEM;
+
+	dmic->gpio_en = devm_gpiod_get_optional(codec->dev,
+						"dmicen", GPIOD_OUT_LOW);
+	if (IS_ERR(dmic->gpio_en))
+		return PTR_ERR(dmic->gpio_en);
 
-	dmic_en = devm_gpiod_get_optional(codec->dev,
-					"dmicen", GPIOD_OUT_LOW);
-	if (IS_ERR(dmic_en))
-		return PTR_ERR(dmic_en);
+	err = device_property_read_u32(codec->dev, "wakeup-delay-ms",
+				       &dmic->wakeup_delay);
+	if (err && (err != -EINVAL))
+		return err;
 
-	snd_soc_codec_set_drvdata(codec, dmic_en);
+	snd_soc_codec_set_drvdata(codec, dmic);
 
 	return 0;
 }
-- 
2.16.1.291.g4437f3f132-goog