linux-kernel - Re: [PATCH 3/3] ASoC: wm8940: Mute also the speaker output

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Date:   Fri, 10 Jun 2022 11:23:31 +0200
From:   Lukasz Majewski <lukma@...x.de>
To:     Mark Brown <broonie@...nel.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com, alsa-devel@...a-project.org,
        Takashi Iwai <tiwai@...e.com>, Jaroslav Kysela <perex@...ex.cz>
Subject: Re: [PATCH 3/3] ASoC: wm8940: Mute also the speaker output

Hi Mark,

> On Mon, Jun 06, 2022 at 05:44:41PM +0200, Lukasz Majewski wrote:
> 
> > Without this change the BTL speaker produces some
> > "distortion" noise when test program
> > (speaker-test -t waw) is ended with ctrl+c.  
> 
> > As our design uses speaker outputs to drive BTL speaker,
> > it was necessary to also mute the speaker via the codec
> > internal WM8940_SPKVOL register with setting
> > WM8940_SPKMUTE bit.  
> 
> This will not interact well with both the user visible control of the
> speaker volume via the Speaker Playback Volume control and the analog
> bypass paths that the device has - it'll change the state of the
> control without generating any events, and cut off any bypassed audio
> that's mixed in.
> 

I'm wondering why it is safe to call DAI's .digital_mute()
callback, which explicitly changes state of the "DAC soft mute enable"
bit (DACMU) ?

And on the other hand it is not correct to just mute the speakers?

> You can probably achieve a similar effect by making the control an
> _AUTODISABLE one which will allow the core to mute the control when
> it's not being used in a way that's not visible to userspace.

The exact definition for the event, which I'm forcing above:

SOC_SINGLE("Speaker Playback Switch", WM8940_SPKVOL,  6, 1, 1),

And there is no SOC_SINGLE_AUTODISABLE() macro available.


The issue I'm trying to fix:

- The mclk clock is stopped (after some time) by imx SOC when I end
  'speaker-test' program with ctrl+c.

- When the clock is not provided (after ~1sec) I do hear a single short
  noise from speakers.

- The other solution (which also works) would be to enable clock once
  (during probe) and then do not disable it till system is powered
  off (yes it is a hack :-) ).


I'm wondering if this can be fixed by some 'amixer' user space switch?

Thanks in advance for help.

Best regards,

Lukasz Majewski

--

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-59 Fax: (+49)-8142-66989-80 Email: lukma@...x.de

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