[PATCH v2] ASoC: fsl_sai: Fix spurious BCLK on resume by clearing BYP

[Chancel Liu <chancel.liu@oss.nxp.com>]

From: Chancel Liu <chancel.liu@nxp.com>

When the BCLK divider ratio is 1:1, fsl_sai_set_bclk() enables bypass
mode by setting BYP, but never clears the bit. The BYP=1 value remains
in the regcache, and is restored by regcache_sync() on the next runtime
resume.

Since BYP=1 combined with BCD=1 immediately outputs the ungated MCLK
as BCLK without waiting for BCE/TE/RE to be enabled, the clock is
driven prematurely before the stream is fully configured, causing
noise on some codecs.

Fix this by clearing BYP and BCI in fsl_sai_hw_free() taking into
account sync mode and the opposite stream's state, so that the regcache
holds BYP=0 before runtime suspend and regcache_sync() on resume will
not restore bypass mode prematurely.

Fixes: a50b7926d015 ("ASoC: fsl_sai: implement 1:1 bclk:mclk ratio support")
Cc: stable@vger.kernel.org
Signed-off-by: Chancel Liu <chancel.liu@nxp.com>
---
Changes in v2:
- Move BYP/BCI clearing from fsl_sai_config_disable() (trigger path)
  to fsl_sai_hw_free() to avoid breaking pause/suspend-resume cycles
  where hw_params() is not called again on unpause/resume.

 sound/soc/fsl/fsl_sai.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c
index 9661602b53c5..d232c8f53061 100644
--- a/sound/soc/fsl/fsl_sai.c
+++ b/sound/soc/fsl/fsl_sai.c
@@ -808,6 +808,8 @@ static int fsl_sai_hw_free(struct snd_pcm_substream *substream,
 	struct fsl_sai *sai = snd_soc_dai_get_drvdata(cpu_dai);
 	bool tx = substream->stream == SNDRV_PCM_STREAM_PLAYBACK;
 	unsigned int ofs = sai->soc_data->reg_offset;
+	int adir = tx ? RX : TX;
+	int dir  = tx ? TX : RX;

 	/* Clear xMR to avoid channel swap with mclk_with_tere enabled case */
 	regmap_write(sai->regmap, FSL_SAI_xMR(tx), 0);
@@ -815,10 +817,29 @@ static int fsl_sai_hw_free(struct snd_pcm_substream *substream,
 	regmap_update_bits(sai->regmap, FSL_SAI_xCR3(tx, ofs),
 			   FSL_SAI_CR3_TRCE_MASK, 0);

-	if (!sai->is_consumer_mode[tx] &&
-	    sai->mclk_streams & BIT(substream->stream)) {
-		clk_disable_unprepare(sai->mclk_clk[sai->mclk_id[tx]]);
-		sai->mclk_streams &= ~BIT(substream->stream);
+	if (!sai->is_consumer_mode[tx]) {
+		bool adir_active = !!(sai->mclk_streams & BIT(!substream->stream));
+		/*
+		 * If opposite stream provides clocks for synchronous mode and
+		 * it is inactive, Clear BYP and BCI
+		 */
+		if (fsl_sai_dir_is_synced(sai, adir) && !adir_active)
+			regmap_update_bits(sai->regmap, FSL_SAI_xCR2(!tx, ofs),
+					   FSL_SAI_CR2_BCI | FSL_SAI_CR2_BYP, 0);
+		/*
+		 * Clear BYP and BCI of current stream if either of:
+		 * 1. current stream doesn't provide clocks for synchronous mode
+		 * 2. current stream provides clocks for synchronous mode but no
+		 *    more stream is active.
+		 */
+		if (!fsl_sai_dir_is_synced(sai, dir) || !adir_active)
+			regmap_update_bits(sai->regmap, FSL_SAI_xCR2(tx, ofs),
+					   FSL_SAI_CR2_BCI | FSL_SAI_CR2_BYP, 0);
+
+		if (sai->mclk_streams & BIT(substream->stream)) {
+			clk_disable_unprepare(sai->mclk_clk[sai->mclk_id[tx]]);
+			sai->mclk_streams &= ~BIT(substream->stream);
+		}
 	}

 	return 0;
--
2.50.1