ASoC: dmic: Add optional wakeup delay

On some systems a delay is needed after switching on the clocks, to allow
the 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 after enabling the mic. A blocking delay
can't be applied in dmic_daiops_trigger() since the function is called
in atomic context. Instead use a DAPM event handler to set the enable
GPIO and apply the delay in the handler.
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/dmic.txt

@@ -8,6 +8,7 @@ Required properties:
 Optional properties:
 	- dmicen-gpios: GPIO specifier for dmic to control start and stop
 	- num-channels: Number of microphones on this DAI
+	- wakeup-delay-ms: Delay (in ms) after enabling the DMIC
 
 Example node:
 
@@ -15,4 +16,5 @@ Example node:
 		compatible = "dmic-codec";
 		dmicen-gpios = <&gpio4 3 GPIO_ACTIVE_HIGH>;
 		num-channels = <1>;
+		wakeup-delay-ms <50>;
 	};

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>
@@ -29,34 +30,33 @@
 #include <sound/soc.h>
 #include <sound/soc-dapm.h>
 
-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 {
+	struct gpio_desc *gpio_en;
+	int wakeup_delay;
+};
 
-	if (!dmic_en)
-		return 0;
+static int dmic_aif_event(struct snd_soc_dapm_widget *w,
+			  struct snd_kcontrol *kcontrol, int event) {
+	struct snd_soc_codec *codec = snd_soc_dapm_to_codec(w->dapm);
+	struct dmic *dmic = snd_soc_codec_get_drvdata(codec);
 
-	switch (cmd) {
-	case SNDRV_PCM_TRIGGER_START:
-	case SNDRV_PCM_TRIGGER_RESUME:
-	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
-		gpiod_set_value(dmic_en, 1);
+	switch (event) {
+	case SND_SOC_DAPM_POST_PMU:
+		if (dmic->gpio_en)
+			gpiod_set_value(dmic->gpio_en, 1);
+
+		if (dmic->wakeup_delay)
+			msleep(dmic->wakeup_delay);
 		break;
-	case SNDRV_PCM_TRIGGER_STOP:
-	case SNDRV_PCM_TRIGGER_SUSPEND:
-	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
-		gpiod_set_value(dmic_en, 0);
+	case SND_SOC_DAPM_POST_PMD:
+		if (dmic->gpio_en)
+			gpiod_set_value(dmic->gpio_en, 0);
 		break;
 	}
 
 	return 0;
 }
 
-static const struct snd_soc_dai_ops dmic_dai_ops = {
-	.trigger	= dmic_daiops_trigger,
-};
-
 static struct snd_soc_dai_driver dmic_dai = {
 	.name = "dmic-hifi",
 	.capture = {
@@ -68,26 +68,33 @@ static struct snd_soc_dai_driver dmic_dai = {
 			| SNDRV_PCM_FMTBIT_S24_LE
 			| SNDRV_PCM_FMTBIT_S16_LE,
 	},
-	.ops    = &dmic_dai_ops,
 };
 
 static int dmic_component_probe(struct snd_soc_component *component)
 {
-	struct gpio_desc *dmic_en;
+	struct dmic *dmic;
+
+	dmic = devm_kzalloc(component->dev, sizeof(*dmic), GFP_KERNEL);
+	if (!dmic)
+		return -ENOMEM;
+
+	dmic->gpio_en = devm_gpiod_get_optional(component->dev,
+						"dmicen", GPIOD_OUT_LOW);
+	if (IS_ERR(dmic->gpio_en))
+		return PTR_ERR(dmic->gpio_en);
 
-	dmic_en = devm_gpiod_get_optional(component->dev,
-					"dmicen", GPIOD_OUT_LOW);
-	if (IS_ERR(dmic_en))
-		return PTR_ERR(dmic_en);
+	device_property_read_u32(component->dev, "wakeup-delay-ms",
+				 &dmic->wakeup_delay);
 
-	snd_soc_component_set_drvdata(component, dmic_en);
+	snd_soc_component_set_drvdata(component, dmic);
 
 	return 0;
 }
 
 static const struct snd_soc_dapm_widget dmic_dapm_widgets[] = {
-	SND_SOC_DAPM_AIF_OUT("DMIC AIF", "Capture", 0,
-			     SND_SOC_NOPM, 0, 0),
+	SND_SOC_DAPM_AIF_OUT_E("DMIC AIF", "Capture", 0,
+			       SND_SOC_NOPM, 0, 0, dmic_aif_event,
+			       SND_SOC_DAPM_POST_PMU | SND_SOC_DAPM_POST_PMD),
 	SND_SOC_DAPM_INPUT("DMic"),
 };