[alsa-devel] [PATCH] ASoC: ssm2602: Fix ADC powerup sequencing

[Marco Felsch]

From: Philipp Zabel <p.zabel at pengutronix.de>

According to the ssm2603 data sheet (control register sequencing), the
digital core should be activated only after all necessary bits in the
power register are enabled, and a delay determined by the decoupling
capacitor on the VMID pin has passed. If the digital core is activated
too early, or even before the ADC is powered up, audible artifacts
appear at the beginning of the recorded signal.

The digital core is also needed for playback, so when recording starts
it may already be enabled. This means we cannot get the power sequence
correct when we want to be able to start recording after playback.

As a workaround put the MIC mute switch into the DAPM routes. This
way we can keep the recording disabled until the MIC Bias has settled
and thus get rid of audible artifacts.

The delay we have to wait depends on a board specific capacitor
connected to the VMID pins, so make the delay configurable in the device
tree.

Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
Signed-off-by: Marco Felsch <m.felsch at pengutronix.de>
---
 .../devicetree/bindings/sound/adi,ssm2602.txt |  7 +++++
 sound/soc/codecs/ssm2602.c                    | 30 +++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/sound/adi,ssm2602.txt b/Documentation/devicetree/bindings/sound/adi,ssm2602.txt
index 3b3302fe399b..9334d48c0462 100644
--- a/Documentation/devicetree/bindings/sound/adi,ssm2602.txt
+++ b/Documentation/devicetree/bindings/sound/adi,ssm2602.txt
@@ -11,9 +11,16 @@ Required properties:
   - reg : the I2C address of the device for I2C, the chip select
           number for SPI.
 
+Optional properties:
+
+  - startup-delay-us : delay between powering on and activating the digital
+                       core, determined by the decoupling capacitor C on the
+		       VMID pin: delay [µs] = C [µF] * 25000 / 3.5
+
  Example:
 
 	ssm2602: ssm2602 at 1a {
 		compatible = "adi,ssm2602";
 		reg = <0x1a>;
+		startup-delay-us = <34000>; /* 4.7 µF * 25000 / 3.5 -> ~34 ms */
 	};
diff --git a/sound/soc/codecs/ssm2602.c b/sound/soc/codecs/ssm2602.c
index 501a4e73b185..1b99f5d44f8d 100644
--- a/sound/soc/codecs/ssm2602.c
+++ b/sound/soc/codecs/ssm2602.c
@@ -26,9 +26,11 @@
  * 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#include <linux/delay.h>
 #include <linux/module.h>
 #include <linux/regmap.h>
 #include <linux/slab.h>
+#include <linux/of.h>
 
 #include <sound/pcm.h>
 #include <sound/pcm_params.h>
@@ -46,6 +48,7 @@ struct ssm2602_priv {
 
 	enum ssm2602_type type;
 	unsigned int clk_out_pwr;
+	u32 startup_delay_us;
 };
 
 /*
@@ -111,7 +114,6 @@ SOC_SINGLE_TLV("Sidetone Playback Volume", SSM2602_APANA, 6, 3, 1,
 
 SOC_SINGLE("Mic Boost (+20dB)", SSM2602_APANA, 0, 1, 0),
 SOC_SINGLE("Mic Boost2 (+20dB)", SSM2602_APANA, 8, 1, 0),
-SOC_SINGLE("Mic Switch", SSM2602_APANA, 1, 1, 1),
 };
 
 /* Output Mixer */
@@ -121,10 +123,26 @@ SOC_DAPM_SINGLE("HiFi Playback Switch", SSM2602_APANA, 4, 1, 0),
 SOC_DAPM_SINGLE("Mic Sidetone Switch", SSM2602_APANA, 5, 1, 0),
 };
 
+static const struct snd_kcontrol_new mic_ctl =
+	SOC_DAPM_SINGLE("Switch", SSM2602_APANA, 1, 1, 1);
+
 /* Input mux */
 static const struct snd_kcontrol_new ssm2602_input_mux_controls =
 SOC_DAPM_ENUM("Input Select", ssm2602_enum[0]);
 
+static int ssm2602_mic_switch_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 ssm2602_priv *ssm2602 = snd_soc_codec_get_drvdata(codec);
+
+	if (ssm2602->startup_delay_us)
+		usleep_range(ssm2602->startup_delay_us,
+			     ssm2602->startup_delay_us * 2);
+
+	return 0;
+}
+
 static const struct snd_soc_dapm_widget ssm260x_dapm_widgets[] = {
 SND_SOC_DAPM_DAC("DAC", "HiFi Playback", SSM2602_PWR, 3, 1),
 SND_SOC_DAPM_ADC("ADC", "HiFi Capture", SSM2602_PWR, 2, 1),
@@ -146,6 +164,9 @@ SND_SOC_DAPM_MIXER("Output Mixer", SSM2602_PWR, 4, 1,
 SND_SOC_DAPM_MUX("Input Mux", SND_SOC_NOPM, 0, 0, &ssm2602_input_mux_controls),
 SND_SOC_DAPM_MICBIAS("Mic Bias", SSM2602_PWR, 1, 1),
 
+SND_SOC_DAPM_SWITCH_E("Mic Switch", SSM2602_APANA, 1, 1, &mic_ctl,
+		ssm2602_mic_switch_event, SND_SOC_DAPM_PRE_PMU),
+
 SND_SOC_DAPM_OUTPUT("LHPOUT"),
 SND_SOC_DAPM_OUTPUT("RHPOUT"),
 SND_SOC_DAPM_INPUT("MICIN"),
@@ -178,9 +199,11 @@ static const struct snd_soc_dapm_route ssm2602_routes[] = {
 	{"LHPOUT", NULL, "Output Mixer"},
 
 	{"Input Mux", "Line", "Line Input"},
-	{"Input Mux", "Mic", "Mic Bias"},
+	{"Input Mux", "Mic", "Mic Switch"},
 	{"ADC", NULL, "Input Mux"},
 
+	{"Mic Switch", NULL, "Mic Bias"},
+
 	{"Mic Bias", NULL, "MICIN"},
 };
 
@@ -645,6 +668,9 @@ int ssm2602_probe(struct device *dev, enum ssm2602_type type,
 	if (ssm2602 == NULL)
 		return -ENOMEM;
 
+	of_property_read_u32(dev->of_node, "startup-delay-us",
+			     &ssm2602->startup_delay_us);
+
 	dev_set_drvdata(dev, ssm2602);
 	ssm2602->type = type;
 	ssm2602->regmap = regmap;
-- 
2.17.0