linux-kernel - Re: Nokia N900 headset detection & MIC Bias + TVOUT

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Message-ID: <20170109193828.rzpyzzl6g3v2nylk@sirena.org.uk>
Date:   Mon, 9 Jan 2017 19:38:28 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Pali Rohár <pali.rohar@...il.com>
Cc:     Tony Lindgren <tony@...mide.com>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        Jarkko Nikula <jarkko.nikula@...mer.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        Nishanth Menon <nm@...com>, Sebastian Reichel <sre@...nel.org>,
        Pavel Machek <pavel@....cz>,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        joerg Reisenweber <joerg@...nmoko.org>,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Nokia N900 headset detection & MIC Bias + TVOUT

On Mon, Jan 09, 2017 at 08:29:53PM +0100, Pali Rohár wrote:
> On Monday 09 January 2017 20:22:01 Mark Brown wrote:

> > point where you need an actual change.  Note that if something holds
> > the microphone bias on (like something using the microphone)
> > separately then that'll take effect so if you really need things to
> > get turned off then that won't work but you probably have trouble
> > anyway in that situation.

> This is needed for cable/jack detection at time when jack is inserted. 
> So before it there cannot be any user of (disconnected) microphone.

That's not going to stop userspace, consider what happens if the headset
gets removed and userspace is slow to stop a recording for example.

> What I need is to enable mic bias, measure ADC of some time period, 
> check status of some GPIOs. Then disable mic bias, measure ADC again and 
> check GPIOs. I in this detection procedure I need to ensure that nobody 
> changes mic bias. So I though that locking the whole procedure could 
> ensure that.

That sounds racy and a bit unusual - what's the actual procedure here?

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