RE: [EXTERNAL] Re: [PATCH] ASoC: max98373: Mark cache dirty before entering sleep

[Ryan Lee <RyanS.Lee@maximintegrated.com>]

> -----Original Message-----
> From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> Sent: Monday, September 27, 2021 7:55 AM
> To: Ryan Lee <RyanS.Lee@maximintegrated.com>; lgirdwood@gmail.com;
> broonie@kernel.org; perex@perex.cz; tiwai@suse.com; yung-
> chuan.liao@linux.intel.com; guennadi.liakhovetski@linux.intel.com; alsa-
> devel@alsa-project.org; linux-kernel@vger.kernel.org
> Cc: sathya.prakash.m.r@intel.com; ryan.lee.maxim@gmail.com
> Subject: [EXTERNAL] Re: [PATCH] ASoC: max98373: Mark cache dirty before
> entering sleep
> 
> EXTERNAL EMAIL
> 
> 
> 
> On 9/24/21 5:13 PM, Ryan Lee wrote:
> > Amp lose its register values in case amp power loss or 'ForceReset'
> > over Soundwire SCP_ctrl register(0x0044) or HW_RESET pin control
> > during the audio suspend and resume.
> > Mark cache dirty before audio suspension to restore existing values
> > when audio resume.
> >
> > Signed-off-by: Ryan Lee <ryans.lee@maximintegrated.com>
> > ---
> >  sound/soc/codecs/max98373-sdw.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/sound/soc/codecs/max98373-sdw.c
> > b/sound/soc/codecs/max98373-sdw.c index dc520effc61c..a7e4a6e880b0
> > 100644
> > --- a/sound/soc/codecs/max98373-sdw.c
> > +++ b/sound/soc/codecs/max98373-sdw.c
> > @@ -259,6 +259,7 @@ static __maybe_unused int
> max98373_suspend(struct device *dev)
> >               regmap_read(max98373->regmap, max98373->cache[i].reg,
> > &max98373->cache[i].val);
> >
> >       regcache_cache_only(max98373->regmap, true);
> > +     regcache_mark_dirty(max98373->regmap);
> 
> We already do the following sequence in max98373_io_init() when the
> amplifier re-attaches:
> 
>         if (max98373->first_hw_init) {
>                 regcache_cache_bypass(max98373->regmap, false);
>                 regcache_mark_dirty(max98373->regmap);
>         }
> 
> I don't see what marking the cache as dirty on suspend might do, we will do a
> sync only in the resume step.
> 
> IIRC this is a patch that we've seen before and removed since it wasn't
> aligned with any other codec driver.
> 
> Does this actually improve anything?
Yes, it does. There was an mute problem report due to amp register reset
during suspend/resume. and we confirmed that the modification 
is effective. (https://partnerissuetracker.corp.google.com/issues/194472331)
The added code helps to re-write valid values in cache to the amp hardware
when audio resume. Same code was there on i2c driver, but not on Soundwire
driver.
>