linux-kernel - Re: [alsa-devel] [PATCH V2 02/10] ASoC: img: Add driver for I2S input controller

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Date:	Thu, 29 Oct 2015 15:42:59 +0000
From:	Damien Horsley <Damien.Horsley@...tec.com>
To:	Mark Brown <broonie@...nel.org>
CC:	<alsa-devel@...a-project.org>,
	James Hartley <James.Hartley@...tec.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] [PATCH V2 02/10] ASoC: img: Add driver for I2S input
 controller

On 28/10/15 23:43, Mark Brown wrote:
> On Wed, Oct 28, 2015 at 09:18:20PM +0000, Damien Horsley wrote:
>> On 28/10/15 01:04, Mark Brown wrote:
> 
>>>> I think it also makes sense to keep the blocks consistent with each
>>>> other. The spdif (out and in), and parallel out, all flush automatically
>>>> when stopped, and the fifo for the i2s out block is cleared when the
>>>> reset is asserted.
> 
>>> This seems like an issue that got missed in the other drivers then.  I'd
>>> expect the trigger operation to be a minimal operation which starts and
>>> stops the data transfer, not doing anything else.
> 
>> The spdif out, spdif in, and parallel out blocks auto-flush whenever
>> they are stopped. It is not possible for software to prevent this behavior.
> 
> Oh, so this isn't the drivers doing this?  In that case it's fine for
> them to do that, if it's what the hardware does it's what the hardware
> does.  It sounded like you were saying that there was similar code in
> the other drivers.
> 

For the I2S In, there is another issue with flushing on stream close. If
the stream is stopped, then reconfigured to use a larger number of
channels (without the stream being closed), then the per-channel fifos
will become inconsistent with each other. The new channels will have no
samples in their FIFOs, while the others may contain samples from the
previous stream.

Would hw_params be the correct place to flush instead?
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