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

[Chancel Liu (OSS)]

> > From: Chancel Liu <chancel.liu@xxxxxxx>
> >
> > 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 together in fsl_sai_config_disable().
> > Also clear BCI, which is programmed together with the bypass case in
> > synchronous mode, so the cached CR2 state is clean and regcache_sync()
> > will not restore bypass mode prematurely on the next resume.
> >
> > Fixes: a50b7926d015 ("ASoC: fsl_sai: implement 1:1 bclk:mclk ratio
> > support")
> > Signed-off-by: Chancel Liu <chancel.liu@xxxxxxx>
> 
> Reviewed-by: Shengjiu Wang <shengjiu.wang@xxxxxxxxx>
> 

Thanks for your review. As sashiko reported this patch has potential
regression. I have to rework on it.

Regards, 
Chancel Liu

> Best regards
> Shengjiu Wang
> > ---
> >  sound/soc/fsl/fsl_sai.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c index
> > 9661602b53c5..4c0626d572a5 100644
> > --- a/sound/soc/fsl/fsl_sai.c
> > +++ b/sound/soc/fsl/fsl_sai.c
> > @@ -847,6 +847,9 @@ static void fsl_sai_config_disable(struct fsl_sai
> *sai, int dir)
> >         regmap_update_bits(sai->regmap, FSL_SAI_xCSR(tx, ofs),
> >                            FSL_SAI_CSR_FR, FSL_SAI_CSR_FR);
> >
> > +       regmap_update_bits(sai->regmap, FSL_SAI_xCR2(tx, ofs),
> > +                          FSL_SAI_CR2_BCI | FSL_SAI_CR2_BYP, 0);
> > +
> >         /*
> >          * For sai master mode, after several open/close sai,
> >          * there will be no frame clock, and can't recover
> > --
> > 2.50.1
> >