[PATCH AUTOSEL 5.2 158/185] SoC: simple-card-utils: set 0Hz to sysclk when shutdown

[Sasha Levin]

From: Katsuhiro Suzuki <katsuhiro@xxxxxxxxxxxxx>

[ Upstream commit 2458adb8f92ad4d07ef7ab27c5bafa1d3f4678d6 ]

This patch set 0Hz to sysclk when shutdown the card.

Some codecs set rate constraints that derives from sysclk. This
mechanism works correctly if machine drivers give fixed frequency.

But simple-audio and audio-graph card set variable clock rate if
'mclk-fs' property exists. In this case, rate constraints will go
bad scenario. For example a codec accepts three limited rates
(mclk / 256, mclk / 384, mclk / 512).

Bad scenario as follows (mclk-fs = 256):
   - Initialize sysclk by correct value (Ex. 12.288MHz)
     - Codec set constraints of PCM rate by sysclk
       48kHz (1/256), 32kHz (1/384), 24kHz (1/512)
   - Play 48kHz sound, it's acceptable
   - Sysclk is not changed

   - Play 32kHz sound, it's acceptable
   - Set sysclk to 8.192MHz (= fs * mclk-fs = 32k * 256)
     - Codec set constraints of PCM rate by sysclk
       32kHz (1/256), 21.33kHz (1/384), 16kHz (1/512)

   - Play 48kHz again, but it's NOT acceptable because constraints
     do not allow 48kHz

So codecs treat 0Hz sysclk as signal of applying no constraints to
avoid this problem.

Signed-off-by: Katsuhiro Suzuki <katsuhiro@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20190907174501.19833-1-katsuhiro@xxxxxxxxxxxxx
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 sound/soc/generic/simple-card-utils.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sound/soc/generic/simple-card-utils.c b/sound/soc/generic/simple-card-utils.c
index f4c6375d11c7a..ef1adf87cbc8b 100644
--- a/sound/soc/generic/simple-card-utils.c
+++ b/sound/soc/generic/simple-card-utils.c
@@ -224,10 +224,17 @@ EXPORT_SYMBOL_GPL(asoc_simple_startup);
 void asoc_simple_shutdown(struct snd_pcm_substream *substream)
 {
 	struct snd_soc_pcm_runtime *rtd = substream->private_data;
+	struct snd_soc_dai *codec_dai = rtd->codec_dai;
+	struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
 	struct asoc_simple_priv *priv = snd_soc_card_get_drvdata(rtd->card);
 	struct simple_dai_props *dai_props =
 		simple_priv_to_props(priv, rtd->num);
 
+	if (dai_props->mclk_fs) {
+		snd_soc_dai_set_sysclk(codec_dai, 0, 0, SND_SOC_CLOCK_IN);
+		snd_soc_dai_set_sysclk(cpu_dai, 0, 0, SND_SOC_CLOCK_OUT);
+	}
+
 	asoc_simple_clk_disable(dai_props->cpu_dai);
 
 	asoc_simple_clk_disable(dai_props->codec_dai);
-- 
2.20.1