linux-kernel - Re: [PATCH 03/16] ASoC: tas2781: disable regmap regcache

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Message-ID: <5f3f0306-799f-4f3b-9e05-fbd300c59d5d@sirena.org.uk>
Date:   Thu, 7 Dec 2023 20:36:22 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Gergo Koteles <soyer@....hu>
Cc:     Shenghao Ding <shenghao-ding@...com>, Kevin Lu <kevin-lu@...com>,
        Baojun Xu <baojun.xu@...com>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        linux-kernel@...r.kernel.org, alsa-devel@...a-project.org
Subject: Re: [PATCH 03/16] ASoC: tas2781: disable regmap regcache

On Thu, Dec 07, 2023 at 09:19:34PM +0100, Gergo Koteles wrote:
> On Thu, 2023-12-07 at 18:20 +0000, Mark Brown wrote:
> > On Thu, Dec 07, 2023 at 12:59:44AM +0100, Gergo Koteles wrote:

> > > The amp has 3 level addressing (BOOK, PAGE, REG).
> > > The regcache couldn't handle it.

> > So the books aren't currently used so the driver actually works?

> It writes to the book 0 and 8c. The initialization works with regcache,
> because it writes also the i2c devices.

I can't see any references to 0x8c in the driver?

> > >  static int tas2781_system_suspend(struct device *dev)
> > > @@ -770,10 +758,7 @@ static int tas2781_system_suspend(struct device *dev)
> > >  		return ret;
> > >  
> > >  	/* Shutdown chip before system suspend */
> > > -	regcache_cache_only(tas_priv->regmap, false);
> > >  	tasdevice_tuning_switch(tas_priv, 1);
> > > -	regcache_cache_only(tas_priv->regmap, true);
> > > -	regcache_mark_dirty(tas_priv->regmap);

> > How can this work over system suspend?  This just removes the cache with
> > no replacement so if the device looses power over suspend (which seems
> > likely) then all the register state will be lost.  A similar issue may
> > potentially exist over runtime suspend on an ACPI system with
> > sufficiently heavily optimised power management.

> In runtime_resume, only one of the two amplifiers goes back.
> The runtime_suspend sets the current book/prog/conf to -1 on all
> devices, and tas2781_hda_playback_hook will restore the
> program/configuration/profile with tasdevice_tuning_switch.

What does "go back" mean?  

> And only one, because tasdevice_change_chn_book directly changes the
> address of i2c_client, so the unlucky one gets invalid values in its
> actual book from regcache_sync.

The code creates the impression that writing to one tas2781 writes to
all of them, is that not the case?

> system_restore doesn't work at all, because regcache_cache_only stays
> true since system_suspend.

Presumably the next runtime resume would make the device writable again?

> It works without the regcache functions.

How would the devices get their configuration restored?

This sounds very much like a case of something working for your specific
system in your specific test through some external factor rather than
working by design, whatever problems might exist it seems fairly obvious
to inspection that this patch would make things worse for other systems.

At a minimum this patch needs a much clearer changelog (all the patches
I looked at could use clearer changelogs) which explains what's going on
here, I would really expect to see something that replaces the use of
the cache sync to restore the device state for example.

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