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Message-ID: <d83615ae-10d9-ca5b-26aa-522b3f10b43f@linux.intel.com>
Date:   Thu, 12 Jan 2023 08:19:40 -0600
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Subject: Re: [PATCH] ASoC: soc-pcm.c: Introduce a count to record the times of
 setting DAIs parameters
To:     Chancel Liu <chancel.liu@nxp.com>, lgirdwood@gmail.com,
        broonie@kernel.org, perex@perex.cz, tiwai@suse.com,
        alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org
References: <20230112065834.580192-1-chancel.liu@nxp.com>
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From:   Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
In-Reply-To: <20230112065834.580192-1-chancel.liu@nxp.com>
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On 1/12/23 00:58, Chancel Liu wrote:
> The commit 1da681e52853 ("ASoC: soc-pcm.c: Clear DAIs parameters after
> stream_active is updated") tries to make sure DAIs parameters can be
> cleared properly through moving the cleanup to the place where
> stream_active is updated. However, it will cause the cleanup only
> happening in soc_pcm_close().
> 
> Suppose a case: aplay -Dhw:0 44100.wav 48000.wav. The case calls
> soc_pcm_open()->soc_pcm_hw_params()->soc_pcm_hw_free()->
> soc_pcm_hw_params()->soc_pcm_hw_free()->soc_pcm_close() in order. The
> parameters would be remained in the system even if the playback of
> 44100.wav is finished.
> 
> The case requires us clearing parameters in phase of soc_pcm_hw_free().
> We shouldn't use stream_active to decide if we must do the cleanup
> since it is finally updated in soc_pcm_close().
> 
> This patch introduces a usage count called hw_params_count in
> snd_soc_dai structure. It records the times of setting parameters to
> this DAI then decreases each time soc_pcm_hw_free() is called. If the
> count decreases to 0, it means this DAI is not used now and we should
> clear the parameters.

what makes you think that the use of hw_params and hw_free is symmetrical?

A couple of years ago we found a case where the FE hw_params failed, and
in that case the BE hw_free was called without the BE hw_params ever
being invoked first. This is due to the DPCM error handling, and as a
result all our hw_free implementations test if the resources are
actually allocated/valid and never assume hw_params was used.

IIRC it's also valid to call hw_params multiple times without calling
hw_free every time.

> Fixes: 1da681e52853 ("ASoC: soc-pcm.c: Clear DAIs parameters after stream_active is updated")
> 
> Signed-off-by: Chancel Liu <chancel.liu@nxp.com>
> ---
>  include/sound/soc-dai.h |  3 +++
>  sound/soc/soc-pcm.c     | 16 +++++++++++-----
>  2 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/include/sound/soc-dai.h b/include/sound/soc-dai.h
> index ea7509672086..a7e589a0fe72 100644
> --- a/include/sound/soc-dai.h
> +++ b/include/sound/soc-dai.h
> @@ -451,6 +451,9 @@ struct snd_soc_dai {
>  	unsigned int channels;
>  	unsigned int sample_bits;
>  
> +	/* Count of setting DAI parameters */
> +	unsigned int hw_params_count;
> +
>  	/* parent platform/codec */
>  	struct snd_soc_component *component;
>  
> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
> index 579a44d81d9a..2c2a5dcf9e06 100644
> --- a/sound/soc/soc-pcm.c
> +++ b/sound/soc/soc-pcm.c
> @@ -711,14 +711,10 @@ static int soc_pcm_clean(struct snd_soc_pcm_runtime *rtd,
>  
>  	if (!rollback) {
>  		snd_soc_runtime_deactivate(rtd, substream->stream);
> -		/* clear the corresponding DAIs parameters when going to be inactive */
> -		for_each_rtd_dais(rtd, i, dai) {
> -			if (snd_soc_dai_active(dai) == 0)
> -				soc_pcm_set_dai_params(dai, NULL);
>  
> +		for_each_rtd_dais(rtd, i, dai)
>  			if (snd_soc_dai_stream_active(dai, substream->stream) == 0)
>  				snd_soc_dai_digital_mute(dai, 1, substream->stream);
> -		}
>  	}
>  
>  	for_each_rtd_dais(rtd, i, dai)
> @@ -949,6 +945,14 @@ static int soc_pcm_hw_clean(struct snd_soc_pcm_runtime *rtd,
>  
>  	snd_soc_dpcm_mutex_assert_held(rtd);
>  
> +	/* clear the corresponding DAIs parameters when hw_params_count decreases to 0 */
> +	for_each_rtd_dais(rtd, i, dai)
> +		if (snd_soc_dai_stream_valid(dai, substream->stream)) {
> +			dai->hw_params_count--;
> +			if (dai->hw_params_count == 0)
> +				soc_pcm_set_dai_params(dai, NULL);
> +		}
> +
>  	/* run the stream event */
>  	snd_soc_dapm_stream_stop(rtd, substream->stream);
>  
> @@ -1051,6 +1055,7 @@ static int __soc_pcm_hw_params(struct snd_soc_pcm_runtime *rtd,
>  
>  		soc_pcm_set_dai_params(codec_dai, &codec_params);
>  		snd_soc_dapm_update_dai(substream, &codec_params, codec_dai);
> +		codec_dai->hw_params_count++;
>  	}
>  
>  	for_each_rtd_cpu_dais(rtd, i, cpu_dai) {
> @@ -1068,6 +1073,7 @@ static int __soc_pcm_hw_params(struct snd_soc_pcm_runtime *rtd,
>  		/* store the parameters for each DAI */
>  		soc_pcm_set_dai_params(cpu_dai, params);
>  		snd_soc_dapm_update_dai(substream, params, cpu_dai);
> +		cpu_dai->hw_params_count++;
>  	}
>  
>  	ret = snd_soc_pcm_component_hw_params(substream, params);