linux-kernel - Re: [PATCH 1/2] ASoC: qcom: Add helper for allocating Soundwire stream runtime

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Date:   Wed, 29 Nov 2023 10:46:52 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Banajit Goswami <bgoswami@...cinc.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, linux-arm-msm@...r.kernel.org,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        linux-sound@...r.kernel.org
Subject: Re: [PATCH 1/2] ASoC: qcom: Add helper for allocating Soundwire
 stream runtime



On 11/29/23 10:35, Krzysztof Kozlowski wrote:
> On 28/11/2023 18:39, Pierre-Louis Bossart wrote:
>>
>>> +int qcom_snd_sdw_startup(struct snd_pcm_substream *substream)
>>> +{
>>> +	struct snd_soc_pcm_runtime *rtd = substream->private_data;
>>> +	struct snd_soc_dai *cpu_dai = snd_soc_rtd_to_cpu(rtd, 0);
>>> +	struct sdw_stream_runtime *sruntime;
>>> +	struct snd_soc_dai *codec_dai;
>>> +	int ret, i;
>>> +
>>> +	sruntime = sdw_alloc_stream(cpu_dai->name);
>>> +	if (!sruntime)
>>> +		return -ENOMEM;
>>> +
>>> +	for_each_rtd_codec_dais(rtd, i, codec_dai) {
>>> +		ret = snd_soc_dai_set_stream(codec_dai, sruntime,
>>> +					     substream->stream);
>>> +		if (ret < 0 && ret != -ENOTSUPP) {
>>
>> I know this is existing code moved into a helper, but out of curiosity
>> why is -ENOTSUPP ignored? Isn't this problematic?
> 
> This is for all DAI links, so if some don't have set_stream callback, we
> assume it is not needed. For example few codecs do not need it because
> they are not on Soundwire bus at all and they don't care about the stream.

Humm, it was my understanding that the substream is mapped 1:1 with a
dailink, so not sure how SoundWire and non-SoundWire DAIs could be part
of the same dailink?

I am not saying this test is silly, just wondering if there is any case
where this error code is returned. Worst-case it's always false but
harmless.

>>
>>> +			dev_err(rtd->dev, "Failed to set sdw stream on %s\n",
>>> +				codec_dai->name);
>>> +			goto err_set_stream;
>>> +		}
>>> +	}
>>
>> Also should the CPU DAIs also be used to set the stream information?
>> it's not clear to me why only the CODEC DAIs are used.
> 
> I don't know, we never did. As you pointed out, I am just moving things
> around, so I don't really know the original intention.

Fair enough, I've been in your shoes :-)
Not always easy to grade 3+ yr code as 'miss', 'bug', 'optimization' or
'feature'...