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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 15 Dec 2022 09:53:12 +0100
From:   Lukasz Majewski <lukma@...x.de>
To:     Mark Brown <broonie@...nel.org>
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

Hi Mark,

> Hi Mark,
> 
> > 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).   
> 
> Ok
> 
> > Looking at the driver the device
> > supports analogue bypass paths to the speaker - these will be broken
> > by your patch  
> 
> I was not aware about this side effect. I just wanted to be sure that
> the speaker is muted.
> 
> > 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.  
> 
> I would be more than happy if I could use for example the 'amixer'
> command to setup the audio correctly without this patch. 
> 
> For example - on this system - before I run any speaker test I need to
> call: amixer -d set 'Speaker Mixer PCM',0 on
> 
> to unmute the system.
> 

This patch steamed from 4.4 Linux. On the newer Linux version the
"distortion" problem is not present anymore.

I will drop this patch.

> >  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. 
> 
> Ok. I will check this as well.
> 
> > 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.  
> 
> Thanks for your hints. I will investigate it further.
> 
> It looks like this patch is some kind of a hack, to fix my system
> configuration and shall be dropped in v2.
> 
> 
> 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




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

Content of type "application/pgp-signature" skipped