linux-kernel - Re: [PATCH] ASoC: soc-pcm: Use delay set in pointer function

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Message-ID: <20180730105434.GI5789@sirena.org.uk>
Date:   Mon, 30 Jul 2018 11:54:34 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Akshu Agrawal <akshu.agrawal@....com>
Cc:     djkurtz@...omium.org, Alexander.Deucher@....com,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM..." 
        <alsa-devel@...a-project.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: soc-pcm: Use delay set in pointer function

On Fri, Jul 27, 2018 at 06:13:42PM +0800, Akshu Agrawal wrote:
> There are cases where a pointer function populates
> runtime->delay, such as:
> ./sound/pci/hda/hda_controller.c
> ./sound/soc/intel/atom/sst-mfld-platform-pcm.c
> 
> Also, in some cases cpu dai used is generic and the pcm
> driver needs to set delay.
> 
> This delay was getting lost and was overwritten by delays
> from codec or cpu dai delay function if exposed.

I'm not 100% clear how this patch is supposed to work.

> --- a/sound/soc/soc-pcm.c
> +++ b/sound/soc/soc-pcm.c
> @@ -1179,6 +1179,9 @@ static snd_pcm_uframes_t soc_pcm_pointer(struct snd_pcm_substream *substream)
>  	snd_pcm_sframes_t codec_delay = 0;
>  	int i;
>  
> +	/* clearing the previous delay */
> +	runtime->delay = 0;
> +
>  	for_each_rtdcom(rtd, rtdcom) {
>  		component = rtdcom->component;
>  

Here we reset runtime->delay to 0.

> @@ -1203,7 +1206,7 @@ static snd_pcm_uframes_t soc_pcm_pointer(struct snd_pcm_substream *substream)
>  	}
>  	delay += codec_delay;
>  
> -	runtime->delay = delay;
> +	runtime->delay += delay;
>  
>  	return offset;
>  }

but here we change the only assignment to delay from a straight
assignment to an accumilation.  I'm a bit confused as to the intended
difference - when will this be doing something other than setting
runtime->delay to the value we originally accumilated in delay which was
what we were doing anyway?

The two examples you mention just do a straight assignment to delay so
they're not going to be compatible with accumilating in delay, it feels
like we'd do better to add an explicit delay operation for them too to
match what we're doing with CODECs but perhaps I'm missing something
here.

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