linux-kernel - Re: [PATCH 3/4] ASoC: wm8940: Mute also the speaker output

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Date:   Wed, 14 Dec 2022 14:19:43 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Lukasz Majewski <lukma@...x.de>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Charles Keepax <ckeepax@...nsource.cirrus.com>,
        Stephen Kitt <steve@....org>, patches@...nsource.cirrus.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] ASoC: wm8940: Mute also the speaker output

On Wed, Dec 14, 2022 at 01:37:42PM +0100, 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.

> @@ -465,9 +465,18 @@ static int wm8940_mute(struct snd_soc_dai *dai, int mute, int direction)
>  {

> +	spkvol_reg &= ~WM8940_SPKMUTE;
> +	if (mute) {
>  		mute_reg |= 0x40;
> +		spkvol_reg |= WM8940_SPKMUTE;
> +	}
> +
> +	ret = snd_soc_component_write(component, WM8940_SPKVOL, spkvol_reg);
> +	if (ret)
> +		return ret;
>  
>  	return snd_soc_component_write(component, WM8940_DAC, mute_reg);

In addition to the issue Charles raised this is simply not what the mute
callback should do, the mute callback should specifically mute the
digital input (with the goal of masking any glitching on there while
clocks are started/stopped).  Looking at the driver the device supports
analogue bypass paths to the speaker - these will be broken by your
patch so if you genuinely need some workaround in this area I'd be
looking at the Speaker Mixer PCM Playback Switch rather than muting the
speaker as a whole.  If the device just can't cope without an input then
ignore_mdown_time might be what you're looking for, it looks like the
device doesn't have any lengthy sleeps in the power up/down paths so
that should be fine so long as it doesn't pop/click.

I'd also check there's not some other system configuration issue here
which is more obvious when the input from the DAC stops getting input,
check that you don't see similar issues when silence is played for
example.  It might be worth checking that none of the analogue bypass
paths are enabled.

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