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

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Message-ID: <20140721090104.GA21400@opensource.wolfsonmicro.com>
Date:	Mon, 21 Jul 2014 10:01:22 +0100
From:	Richard Fitzgerald <rf@...nsource.wolfsonmicro.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	perex@...ex.cz, tiwai@...e.de, 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 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
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