linux-kernel - Re: [PATCH 1/2] ASoC: qcom: sdm845: handle soundwire stream

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Date:   Wed, 18 Mar 2020 10:26:47 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        broonie@...nel.org
Cc:     alsa-devel@...a-project.org, lgirdwood@...il.com, perex@...ex.cz,
        linux-kernel@...r.kernel.org, vkoul@...nel.org
Subject: Re: [PATCH 1/2] ASoC: qcom: sdm845: handle soundwire stream



>>>       for_each_rtd_codec_dais(rtd, i, codec_dai) {
>>> +        sruntime = snd_soc_dai_get_sdw_stream(codec_dai,
>>> +                              substream->stream);
>>> +        if (sruntime != ERR_PTR(-ENOTSUPP))
>>> +            pdata->sruntime[cpu_dai->id] = sruntime;
>>> +        else
>>> +            pdata->sruntime[cpu_dai->id] = NULL;
>>> +
>>
>> Can you explain this part?
>> The get_sdw_stream() is supposed to return what was set by 
>> set_sdw_stream(), so if it's not supported isn't this an error?
> 
> In this case its not an error because we have
> totally 3 codecs in this path.
> One wcd934x Slimbus codec and two wsa881x Soundwire Codec.
> 
> wcd934x codec side will return ENOTSUPP which is not an error.

I must admit I am quite confused here.
After reading your response, I thought this was a case of codec-to-codec 
dailink, but then you also have a notion of cpu_dai?

>>
>>>           ret = snd_soc_dai_get_channel_map(codec_dai,
>>>                   &tx_ch_cnt, tx_ch, &rx_ch_cnt, rx_ch);
>>> @@ -425,8 +437,65 @@ static void  sdm845_snd_shutdown(struct 
>>> snd_pcm_substream *substream)
>>>       }
>>>   }
>>> +static int sdm845_snd_prepare(struct snd_pcm_substream *substream)
>>> +{
>>> +    struct snd_soc_pcm_runtime *rtd = substream->private_data;
>>> +    struct sdm845_snd_data *data = snd_soc_card_get_drvdata(rtd->card);
>>> +    struct snd_soc_dai *cpu_dai = rtd->cpu_dai;
>>> +    struct sdw_stream_runtime *sruntime = data->sruntime[cpu_dai->id];
>>> +    int ret;
>>> +
>>> +    if (!sruntime)
>>> +        return 0;
>>
>> same here, isn't this an error?
> 
> These callbacks are used for other dais aswell in this case
> HDMI, Slimbus and Soundwire, so sruntime being null is not treated as 
> error.

Same comment, how does the notion of cpu_dai come in the picture for a 
SoundWire dailink?
Would you mind listing what the components of the dailinks are?