[PATCH 5/9] ASoC: ssm2602: Add workaround for playback with external MCLK

["Paweł Anikiel" <pan@semihalf.com>]

Apply a workaround for what seems to be a hardware quirk: when using
an external MCLK signal, powering on Output and DAC for the first time
produces output distortions unless they're powered together with whole
chip power.

The workaround powers them on in probe for the first time, as doing it
later may be impossible (e.g. when starting playback while recording,
whole chip power will already be on).

Here are some initialization sequences run after all other control
registers were set (`ssmset reg val` sets the value of a register
via i2c):

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

Here are some sequences run at the very start before a sw reset (and
later using one of the NOT OK sequences from above):

  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

This was tested on a Google Chameleon v3 board using an SSM2603 with an
external MCLK. This doesn't seem to just be a PCB issue, as this was
also observed on a ZYBO Z7-10:
https://ez.analog.com/audio/f/q-a/543726/solved-ssm2603-right-output-offset-issue/480229

Signed-off-by: Paweł Anikiel <pan@semihalf.com>
---
 sound/soc/codecs/ssm2602.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/sound/soc/codecs/ssm2602.c b/sound/soc/codecs/ssm2602.c
index cbbe83b85ada..021e0c860fa1 100644
--- a/sound/soc/codecs/ssm2602.c
+++ b/sound/soc/codecs/ssm2602.c
@@ -589,6 +589,17 @@ static int ssm260x_component_probe(struct snd_soc_component *component)
 		return ret;
 	}
 
+	/* Workaround for what seems to be a hardware quirk: when using an
+	 * external MCLK signal, powering on Output and DAC for the first
+	 * time produces output distortions unless they're powered together
+	 * with whole chip power. We power them here for the first time,
+	 * as doing it later may be impossible (e.g. when starting playback
+	 * while recording, whole chip power will already be on)
+	 */
+	regmap_write(ssm2602->regmap, SSM2602_ACTIVE, 0x01);
+	regmap_write(ssm2602->regmap, SSM2602_PWR,    0x07);
+	regmap_write(ssm2602->regmap, SSM2602_RESET,  0x00);
+
 	/* set the update bits */
 	regmap_update_bits(ssm2602->regmap, SSM2602_LINVOL,
 			    LINVOL_LRIN_BOTH, LINVOL_LRIN_BOTH);
-- 
2.40.0.634.g4ca3ef3211-goog