linux-kernel - Re: [PATCH] ASoC: dmaengine_pcm: Consider DMA cache caused delay in pointer callback

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Date:   Mon, 10 Feb 2020 16:59:28 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Mark Brown <broonie@...nel.org>
CC:     Takashi Iwai <tiwai@...e.de>, <lgirdwood@...il.com>,
        <tiwai@...e.com>, <perex@...ex.cz>, <lars@...afoo.de>,
        <alsa-devel@...a-project.org>, <vkoul@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: dmaengine_pcm: Consider DMA cache caused delay in
 pointer callback



On 10/02/2020 16.37, Mark Brown wrote:
> On Mon, Feb 10, 2020 at 04:28:44PM +0200, Peter Ujfalusi wrote:
>> On 10/02/2020 16.21, Takashi Iwai wrote:
> 
>>>>  	delay += codec_delay;
>>>>  
>>>> -	runtime->delay = delay;
>>>> +	runtime->delay += delay;
> 
>>> Is it correct?
>>> delay already takes runtime->delay as its basis, so it'll result in a
>>> double.
> 
>> The delay here is coming from the DAI and the codec.
>> The runtime->delay hold the PCM (DMA) caused delay.
> 
> I think Takashi's point here (and a query I have) is that we end up with
> 
> 	delay = runtime->delay;
> 	delay += stuff;
> 	runtime->delay += delay;
> 
> which is equivalent to
> 
> 	runtime->delay = (runtime->delay * 2) + stuff;
> 
> and that's a bit surprising.

I see, I have missed what
9fb4c2bf130b ASoC: soc-pcm: Use delay set in component pointer function

did.
the soc-pcm part of the patch can be dropped then.

- Péter

Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
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