linux-kernel - Re: [PATCH] ASoC: arizona: Disable AIF TX/RX before configuring it

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Date:	Mon, 21 Jul 2014 11:33:27 +0100
From:	Richard Fitzgerald <rf@...nsource.wolfsonmicro.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Mark Brown <broonie@...nel.org>, perex@...ex.cz,
	lgirdwood@...il.com, patches@...nsource.wolfsonmicro.com,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ASoC: arizona: Disable AIF TX/RX before configuring it

On Mon, Jul 21, 2014 at 11:04:56AM +0200, Takashi Iwai wrote:
> At Mon, 21 Jul 2014 10:01:22 +0100,
> Richard Fitzgerald wrote:
> > 
> > On Thu, Jul 17, 2014 at 08:42:15PM +0100, Mark Brown wrote:
> > > On Wed, Jul 16, 2014 at 01:10:39PM +0100, Richard Fitzgerald wrote:
> > > 
> > > > If we don't disable the AIF TX/RX then we may fall into a
> > > > situation where the new AIF settings are ignored by the device.
> > > > For example, this problem manifests when switching between
> > > > different sample rates.
> > > 
> > > So, what this does is momentarily disable the AIF when reconfiguring.
> > > That will glitch any running audio, making me wonder if the driver
> > > shouldn't be returning an error or at least complaining if it has to
> > > reconfigure instead.  What's the use case where this might get
> > > triggered?
> > 
> > The case being fixed is like this:
> > 
> > aplay 48kHz.wav; aplay 96kHz.wav
> > 
> > The second open happens before pmdown_time so the AIF is still enabled.
> > Writes to the AIF config registers only take effect if the AIF is disabled.
> > Without this patch, the 96kHz.wav will play at 48kHz
> 
> If the glitch really matters, the driver can minimize by checking the
> change of sample rate and doing temporary turn on/off only when
> required.
> 
> 
> Takashi

That's a fair point.
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