linux-kernel - Re: [alsa-devel] [PATCH 5/5 v4] ASoC: dwc: Update DOCUMENTATION for I2S Driver

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Date:	Fri, 8 Apr 2016 17:52:13 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Jose Abreu <Jose.Abreu@...opsys.com>,
	Mark Brown <broonie@...nel.org>
Cc:	alsa-devel@...a-project.org, lgirdwood@...il.com, airlied@...ux.ie,
	Vineet.Gupta1@...opsys.com, Alexey.Brodkin@...opsys.com,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	CARLOS.PALMINHA@...opsys.com, tiwai@...e.com,
	linux-snps-arc@...ts.infradead.org, architt@...eaurora.org
Subject: Re: [alsa-devel] [PATCH 5/5 v4] ASoC: dwc: Update DOCUMENTATION for
 I2S Driver

On 04/08/2016 12:06 PM, Jose Abreu wrote:
> Hi Mark,
> 
> 
> On 07-04-2016 18:53, Mark Brown wrote:
>> On Thu, Apr 07, 2016 at 05:53:59PM +0100, Jose Abreu wrote:
>>
>>> + Optional properties:
>>> + - snps,use-dmaengine: If set the driver will use ALSA DMA engine. If set
>>> +   it is required to use the properties 'dmas' and 'dma-names'.
>> This is not a good interface, it's describing Linux internal APIs.  If
>> the device needs to operate in PIO mode it should just do that.
> 
> I added this interface because there is no direct way to check if DMA is
> available on the I2S controller so it is not possible to automatically change
> between DMA and PIO mode. As the I2S controller can be built with or without DMA
> support it is necessary to somehow check if DMA is enabled or not and according
> to that use either ALSA DMA engine or the custom platform driver sent in these
> patches. I did not want to remove drivers functionality so I added this property
> to the DT. This way a user can select between DMA and PIO mode.

That's OK, but you need to describe the hardware, not the indented behavior
of the software driver.