[PATCH] ASoC: cs42l51: manage mclk shutdown delay

[Olivier Moysan <olivier.moysan@st.com>]

A delay must be introduced before the shutdown down of the mclk,
as stated in CS42L51 datasheet. Otherwise the codec may
produce some noise after the end of DAPM power down sequence.
The delay between DAC and CLOCK_SUPPLY widgets is too short.
Add a delay in mclk shutdown request to manage the shutdown delay
explicitly. From experiments, at least 10ms delay is necessary.
Set delay to 20ms as recommended in Documentation/timers/timers-howto.rst
when using msleep().

Signed-off-by: Olivier Moysan <olivier.moysan@st.com>
---
Recommended Power-Down Sequence:
(see https://statics.cirrus.com/pubs/proDatasheet/CS42L51_F2.pdf)
1.    Mute the DACs and ADCs.
2.    Disable soft ramp and zero-cross volume transitions
3.    Set the PDN bit to 1.
4.    Wait at least 100 μs.
The codec will be fully powered down after this 100 μs delay.
Prior to the removal of the master clock(MCLK),
this delay of at least 100 μs must be implemented after step 3
to avoid premature disruption of the codec’s power down sequence.
---
 sound/soc/codecs/cs42l51.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/sound/soc/codecs/cs42l51.c b/sound/soc/codecs/cs42l51.c
index 097c4e8d9950..d151a1aa313e 100644
--- a/sound/soc/codecs/cs42l51.c
+++ b/sound/soc/codecs/cs42l51.c
@@ -254,8 +254,25 @@ static const struct snd_soc_dapm_widget cs42l51_dapm_widgets[] = {
 		&cs42l51_adcr_mux_controls),
 };
 
+static int mclk_event(struct snd_soc_dapm_widget *w,
+		      struct snd_kcontrol *kcontrol, int event)
+{
+	struct snd_soc_component *comp = snd_soc_dapm_to_component(w->dapm);
+	struct cs42l51_private *cs42l51 = snd_soc_component_get_drvdata(comp);
+
+	if (SND_SOC_DAPM_EVENT_ON(event))
+		return clk_prepare_enable(cs42l51->mclk_handle);
+
+	/* Delay mclk shutdown to fulfill power-down sequence requirements */
+	msleep(20);
+	clk_disable_unprepare(cs42l51->mclk_handle);
+
+	return 0;
+}
+
 static const struct snd_soc_dapm_widget cs42l51_dapm_mclk_widgets[] = {
-	SND_SOC_DAPM_CLOCK_SUPPLY("MCLK")
+	SND_SOC_DAPM_SUPPLY("MCLK", SND_SOC_NOPM, 0, 0, mclk_event,
+			    SND_SOC_DAPM_PRE_PMU | SND_SOC_DAPM_POST_PMD),
 };
 
 static const struct snd_soc_dapm_route cs42l51_routes[] = {
-- 
2.17.1