linux-kernel - Re: [RFC PATCH v2] ASoC: soc-pcm: Optimize hw

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Message-ID: <1328ff08-1de7-4c62-b8f7-b09e15f50737@linux.dev>
Date: Fri, 23 May 2025 11:55:48 +0200
From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>
To: Péter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
 "Sheetal ." <sheetal@...dia.com>, broonie@...nel.org, lgirdwood@...il.com,
 perex@...ex.cz, tiwai@...e.com, linux-sound@...r.kernel.org
Cc: linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
 jonathanh@...dia.com, thierry.reding@...il.com, mkumard@...dia.com,
 spujar@...dia.com
Subject: Re: [RFC PATCH v2] ASoC: soc-pcm: Optimize hw_params() BE DAI call

On 5/13/25 13:10, Péter Ujfalusi wrote:
> 
> 
> On 08/04/2025 11:30, Sheetal . wrote:
>> From: Sheetal <sheetal@...dia.com>
>>
>> The hw_params() function for BE DAI was being called multiple times due
>> to an unnecessary SND_SOC_DPCM_STATE_HW_PARAMS state check.
>>
>> Remove the redundant state check to ensure hw_params() is called only once
>> per BE DAI configuration.
> 
> The first sentence tells that the hw_params() of the BE is called
> multiple times.
> 
> The second sentence states that the check is redundant then tells that
> it is removed to not call the hw_params() of the BE, so the check was
> not redundant, it got exercised.
> 
> Which one is true?
> 
> Under what circumstance the __soc_pcm_hw_params() got called multiple
> times? Was it normal or was it error? What causes it?

I share Peter's question. The code has been around since 2016, in what case would the existing logic need to be updated?

One key point is that hw_params() may be called multiple times with different parameters, it's a feature and not a bug. If a call to hw_params() changes an internal state, a follow-up call to hw_params() shall undo the initial state change and rerun the appropriate configuration.

>> Signed-off-by: Sheetal <sheetal@...dia.com>
>> ---
>> Changes in v2:
>> - Update commit message as its not a fix.
>> - Marked as RFC patch as it requires feedback from other users
>>   perspective as well.
>> - The patch is being sent separately as other patch is not RFC.
>>
>>  sound/soc/soc-pcm.c | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
>> index d7f6d3a6d312..c73be27c4ecb 100644
>> --- a/sound/soc/soc-pcm.c
>> +++ b/sound/soc/soc-pcm.c
>> @@ -2123,7 +2123,6 @@ int dpcm_be_dai_hw_params(struct snd_soc_pcm_runtime *fe, int stream)
>>  			continue;
>>  
>>  		if ((be->dpcm[stream].state != SND_SOC_DPCM_STATE_OPEN) &&
>> -		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_PARAMS) &&
>>  		    (be->dpcm[stream].state != SND_SOC_DPCM_STATE_HW_FREE))
>>  			continue;
>>  
>