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Subject: Re: [PATCH] ASoC: dmaengine_pcm: Consider DMA cache caused delay in
 pointer callback
To:     Takashi Iwai <tiwai@suse.de>
CC:     <broonie@kernel.org>, <lgirdwood@gmail.com>, <tiwai@suse.com>,
        <perex@perex.cz>, <lars@metafoo.de>, <alsa-devel@alsa-project.org>,
        <vkoul@kernel.org>, <linux-kernel@vger.kernel.org>
References: <20200210140423.10232-1-peter.ujfalusi@ti.com>
 <s5hmu9qfrq7.wl-tiwai@suse.de>
From:   Peter Ujfalusi <peter.ujfalusi@ti.com>
Message-ID: <15c7df10-cf9f-109c-3cbf-e73af7f4f66a@ti.com>
Date:   Mon, 10 Feb 2020 16:28:44 +0200
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Hi Takashi,

On 10/02/2020 16.21, Takashi Iwai wrote:
> On Mon, 10 Feb 2020 15:04:23 +0100,
> Peter Ujfalusi wrote:
>>
>> Some DMA engines can have big FIFOs which adds to the latency.
>> The DMAengine framework can report the FIFO utilization in bytes. Use this
>> information for the delay reporting.
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
>> ---
>> Hi,
>>
>> 5.6-rc1 now have support for reporting the DMA cached data.
>> With this patch we can include it to the delay calculation.
>> The first DMA driver which reports this is the TI K3 UDMA driver.
>>
>> Regards,
>> Peter
>>
>>  sound/core/pcm_dmaengine.c | 6 ++++++
>>  sound/soc/soc-pcm.c        | 2 +-
>>  2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
>> index 5749a8a49784..4f1395fd0160 100644
>> --- a/sound/core/pcm_dmaengine.c
>> +++ b/sound/core/pcm_dmaengine.c
>> @@ -247,9 +247,15 @@ snd_pcm_uframes_t snd_dmaengine_pcm_pointer(struct snd_pcm_substream *substream)
>>  
>>  	status = dmaengine_tx_status(prtd->dma_chan, prtd->cookie, &state);
>>  	if (status == DMA_IN_PROGRESS || status == DMA_PAUSED) {
>> +		struct snd_pcm_runtime *runtime = substream->runtime;
>> +		int sample_bits = snd_pcm_format_physical_width(runtime->format);
>> +
>>  		buf_size = snd_pcm_lib_buffer_bytes(substream);
>>  		if (state.residue > 0 && state.residue <= buf_size)
>>  			pos = buf_size - state.residue;
>> +
>> +		sample_bits *= runtime->channels;
>> +		runtime->delay = state.in_flight_bytes / (sample_bits / 8);
> 
> Can this be simply bytes_to_frames()?
> 
> 		runtime->delay = bytes_to_frames(runtime, state.in_flight_bytes);

Certainly it can, I looked at various helper but somehow missed the
bytes_to_frames().

I'll send v2 in about an hour.


> 
>>  	}
>>  
>>  	return bytes_to_frames(substream->runtime, pos);
>> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
>> index ff1b7c7078e5..58ef508d70a3 100644
>> --- a/sound/soc/soc-pcm.c
>> +++ b/sound/soc/soc-pcm.c
>> @@ -1151,7 +1151,7 @@ static snd_pcm_uframes_t soc_pcm_pointer(struct snd_pcm_substream *substream)
>>  	}
>>  	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.

> 
> thanks,
> 
> Takashi
> 

- Péter

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