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

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Date:   Mon, 10 Feb 2020 15:21:20 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     <broonie@...nel.org>, <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 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@...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);

>  	}
>  
>  	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.


thanks,

Takashi