[v3] ASoC: max98357a: avoid speaker pop when playback startup

[mac.chiang@intel.com]

From: Mac Chiang <mac.chiang@intel.com>

Loud speaker pop happens during playback even when in slience
playback. Specify Max98357a amp delay times to make sure
clocks are always earlier than sdmode on.

Signed-off-by: Mac Chiang <mac.chiang@intel.com>
---
Changelog:
  v3:
    - rebase to branch for-next
  v2:
    - added device_property_read_u32() func
---
---
 .../devicetree/bindings/sound/max98357a.txt        |  4 ++
 sound/soc/codecs/max98357a.c                       | 55 ++++++++++++++++++----
 2 files changed, 50 insertions(+), 9 deletions(-)

diff --git a/Documentation/devicetree/bindings/sound/max98357a.txt b/Documentation/devicetree/bindings/sound/max98357a.txt
index 28645a2..4bce14c 100644
--- a/Documentation/devicetree/bindings/sound/max98357a.txt
+++ b/Documentation/devicetree/bindings/sound/max98357a.txt
@@ -9,6 +9,10 @@ Optional properties:
 - sdmode-gpios : GPIO specifier for the chip's SD_MODE pin.
         If this option is not specified then driver does not manage
         the pin state (e.g. chip is always on).
+- sdmode-delay : specify delay time for SD_MODE pin.
+        If this option is specified, which means it's required i2s clocks
+        ready before SD_MODE is unmuted in order to avoid the speaker pop noise.
+        It's observed that 5ms is sufficient.
 
 Example:
 
diff --git a/sound/soc/codecs/max98357a.c b/sound/soc/codecs/max98357a.c
index 6f724c9..6f0e28f 100644
--- a/sound/soc/codecs/max98357a.c
+++ b/sound/soc/codecs/max98357a.c
@@ -19,24 +19,42 @@
 #include <sound/soc-dai.h>
 #include <sound/soc-dapm.h>
 
+struct max98357a_priv {
+	struct delayed_work enable_sdmode_work;
+	struct gpio_desc *sdmode;
+	unsigned int sdmode_delay;
+};
+
+static void max98357a_enable_sdmode_work(struct work_struct *work)
+{
+	struct max98357a_priv *max98357a =
+	container_of(work, struct max98357a_priv,
+			enable_sdmode_work.work);
+
+	gpiod_set_value(max98357a->sdmode, 1);
+}
+
 static int max98357a_daiops_trigger(struct snd_pcm_substream *substream,
 		int cmd, struct snd_soc_dai *dai)
 {
-	struct gpio_desc *sdmode = snd_soc_dai_get_drvdata(dai);
+	struct max98357a_priv *max98357a = snd_soc_dai_get_drvdata(dai);
 
-	if (!sdmode)
+	if (!max98357a->sdmode)
 		return 0;
 
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_RESUME:
 	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
-		gpiod_set_value(sdmode, 1);
+		queue_delayed_work(system_power_efficient_wq,
+				&max98357a->enable_sdmode_work,
+				msecs_to_jiffies(max98357a->sdmode_delay));
 		break;
 	case SNDRV_PCM_TRIGGER_STOP:
 	case SNDRV_PCM_TRIGGER_SUSPEND:
 	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
-		gpiod_set_value(sdmode, 0);
+		cancel_delayed_work_sync(&max98357a->enable_sdmode_work);
+		gpiod_set_value(max98357a->sdmode, 0);
 		break;
 	}
 
@@ -90,14 +108,33 @@ static struct snd_soc_dai_driver max98357a_dai_driver = {
 
 static int max98357a_platform_probe(struct platform_device *pdev)
 {
-	struct gpio_desc *sdmode;
+	struct max98357a_priv *max98357a;
+	int ret;
 
-	sdmode = devm_gpiod_get_optional(&pdev->dev,
+	max98357a = devm_kzalloc(&pdev->dev, sizeof(*max98357a), GFP_KERNEL);
+
+	if (!max98357a)
+		return -ENOMEM;
+
+	max98357a->sdmode = devm_gpiod_get_optional(&pdev->dev,
 				"sdmode", GPIOD_OUT_LOW);
-	if (IS_ERR(sdmode))
-		return PTR_ERR(sdmode);
 
-	dev_set_drvdata(&pdev->dev, sdmode);
+	if (IS_ERR(max98357a->sdmode))
+		return PTR_ERR(max98357a->sdmode);
+
+	ret = device_property_read_u32(&pdev->dev, "sdmode-delay",
+					&max98357a->sdmode_delay);
+
+	if (ret) {
+		max98357a->sdmode_delay = 0;
+		dev_dbg(&pdev->dev,
+			"no optional property 'sdmode-delay' found, default: no delay\n");
+	}
+
+	dev_set_drvdata(&pdev->dev, max98357a);
+
+	INIT_DELAYED_WORK(&max98357a->enable_sdmode_work,
+				max98357a_enable_sdmode_work);
 
 	return devm_snd_soc_register_component(&pdev->dev,
 			&max98357a_component_driver,
-- 
2.7.4