[PATCH v2 7/7] ASoC: ssm2602: Add workaround for playback distortions

["Paweł Anikiel" <pan@semihalf.com>]

Apply a workaround for what appears to be a hardware quirk.

The problem seems to happen when enabling "whole chip power" (bit D7
register R6) for the very first time after the chip receives power. If
either "output" (D4) or "DAC" (D3) aren't powered on at that time,
playback becomes very distorted later on.

This happens on the Google Chameleon v3, as well as on a ZYBO Z7-10:
https://ez.analog.com/audio/f/q-a/543726/solved-ssm2603-right-output-offset-issue/480229
I suspect this happens only when using an external MCLK signal (which
is the case for both of these boards).

Here are some experiments run on a Google Chameleon v3. These were run
in userspace using a wrapper around the i2cset utility:
ssmset() {
        i2cset -y 0 0x1a $(($1*2)) $2
}

For each of the following sequences, we apply power to the ssm2603
chip, set the configuration registers R0-R5 and R7-R8, run the selected
sequence, and check for distortions on playback.

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x07 # chip, out, dac
  OK

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x87 # out, dac
  ssmset 0x06 0x07 # chip
  OK

  (disable MCLK)
  ssmset 0x09 0x01 # core
  ssmset 0x06 0x1f # chip
  ssmset 0x06 0x07 # out, dac
  (enable MCLK)
  OK

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x1f # chip
  ssmset 0x06 0x07 # out, dac
  NOT OK

  ssmset 0x06 0x1f # chip
  ssmset 0x09 0x01 # core
  ssmset 0x06 0x07 # out, dac
  NOT OK

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x0f # chip, out
  ssmset 0x06 0x07 # dac
  NOT OK

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x17 # chip, dac
  ssmset 0x06 0x07 # out
  NOT OK

For each of the following sequences, we apply power to the ssm2603
chip, run the selected sequence, issue a reset with R15, configure
R0-R5 and R7-R8, run one of the NOT OK sequences from above, and check
for distortions.

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x07 # chip, out, dac
  OK

  (disable MCLK)
  ssmset 0x09 0x01 # core
  ssmset 0x06 0x07 # chip, out, dac
  (enable MCLK after reset)
  NOT OK

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x17 # chip, dac
  NOT OK

  ssmset 0x09 0x01 # core
  ssmset 0x06 0x0f # chip, out
  NOT OK

  ssmset 0x06 0x07 # chip, out, dac
  NOT OK

Signed-off-by: Paweł Anikiel <pan@semihalf.com>
---
 sound/soc/codecs/ssm2602.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/sound/soc/codecs/ssm2602.c b/sound/soc/codecs/ssm2602.c
index 00b60369b029..c29324403e9d 100644
--- a/sound/soc/codecs/ssm2602.c
+++ b/sound/soc/codecs/ssm2602.c
@@ -53,6 +53,18 @@ static const struct reg_default ssm2602_reg[SSM2602_CACHEREGNUM] = {
 	{ .reg = 0x09, .def = 0x0000 }
 };
 
+/*
+ * ssm2602 register patch
+ * Workaround for playback distortions after power up: activates digital
+ * core, and then powers on output, DAC, and whole chip at the same time
+ */
+
+static const struct reg_sequence ssm2602_patch[] = {
+	{ SSM2602_ACTIVE, 0x01 },
+	{ SSM2602_PWR,    0x07 },
+	{ SSM2602_RESET,  0x00 },
+};
+
 
 /*Appending several "None"s just for OSS mixer use*/
 static const char *ssm2602_input_select[] = {
@@ -598,6 +610,9 @@ static int ssm260x_component_probe(struct snd_soc_component *component)
 		return ret;
 	}
 
+	regmap_register_patch(ssm2602->regmap, ssm2602_patch,
+			      ARRAY_SIZE(ssm2602_patch));
+
 	/* set the update bits */
 	regmap_update_bits(ssm2602->regmap, SSM2602_LINVOL,
 			    LINVOL_LRIN_BOTH, LINVOL_LRIN_BOTH);
-- 
2.40.1.521.gf1e218fcd8-goog