[PATCH v1] ASoC: simple-card-utils: set CPU sysclk before codec for mclk-fs

[Stefano Radaelli <stefano.radaelli21@gmail.com>]

From: Stefano Radaelli <stefano.r@variscite.com>

When simple-audio-card uses simple-audio-card,mclk-fs,
simple_util_hw_params() programs sysclk for codec DAIs and CPU DAIs.

Some CPU DAIs may apply the final MCLK rate as part of their .set_sysclk()
callback (e.g. by changing the underlying clock rate via clk_set_rate()).
If codec sysclk is configured before the CPU DAI applies the final
MCLK rate, the codec may configure its internal clocking based on a
non-final MCLK setting, leading to an incorrect clocking state on the
first playback after boot.

This behaviour was observed on i.MX95 systems using fsl_sai with
downstream kernels, which made the issue visible.
However, the problem is generic and can affect any setup where the
CPU DAI applies the final MCLK rate in set_sysclk() while
simple-audio-card uses mclk-fs.

A reproducible symptom is that the first playback runs at the wrong speed
("slow" audio), while subsequent playbacks work correctly.

Example setup:
  - CPU DAI: fsl_sai (i.MX95)
  - Codec: wm8904
  - simple-audio-card,mclk-fs enabled

Reproducer:
  aplay -D hw:wm8904audio /home/Front_Center_8k.wav

Debug evidence:
ftrace showed snd_soc_dai_set_sysclk() called from simple_util_hw_params
for both codec and CPU DAIs, and confirmed wm8904_set_sysclk() ran before
the CPU DAI sysclk call, and the CPU DAI then applied the final
MCLK settings.

Fix this by setting the CPU DAI sysclk before the codec sysclk
when mclk-fs is used, so that the codec always configures its internal
clocking based on the final MCLK rate.

Signed-off-by: Stefano Radaelli <stefano.r@variscite.com>
---
 sound/soc/generic/simple-card-utils.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/sound/soc/generic/simple-card-utils.c b/sound/soc/generic/simple-card-utils.c
index bdc02e85b089..50f60e4996a5 100644
--- a/sound/soc/generic/simple-card-utils.c
+++ b/sound/soc/generic/simple-card-utils.c
@@ -501,15 +501,21 @@ int simple_util_hw_params(struct snd_pcm_substream *substream,
 				goto end;
 		}
 
-		for_each_rtd_codec_dais(rtd, i, sdai) {
-			pdai = simple_props_to_dai_codec(props, i);
+		/*
+		 * When mclk-fs is used, some CPU DAIs may change the
+		 * actual MCLK rate in set_sysclk() (e.g. via clk_set_rate()).
+		 * Configure CPU DAI first so codec clocking/FLL sees
+		 * the final MCLK rate.
+		 */
+		for_each_rtd_cpu_dais(rtd, i, sdai) {
+			pdai = simple_props_to_dai_cpu(props, i);
 			ret = snd_soc_dai_set_sysclk(sdai, 0, mclk, pdai->clk_direction);
 			if (ret && ret != -ENOTSUPP)
 				goto end;
 		}
 
-		for_each_rtd_cpu_dais(rtd, i, sdai) {
-			pdai = simple_props_to_dai_cpu(props, i);
+		for_each_rtd_codec_dais(rtd, i, sdai) {
+			pdai = simple_props_to_dai_codec(props, i);
 			ret = snd_soc_dai_set_sysclk(sdai, 0, mclk, pdai->clk_direction);
 			if (ret && ret != -ENOTSUPP)
 				goto end;

base-commit: b7ff7151e653aa296ab6c5495b2c1ab7c21eb250
-- 
2.47.3