[PATCH 1/4] ASoC: soc-pcm: dpcm: fix playback/capture checks

[Stephan Gerhold]

Hi Pierre,

On Mon, Jun 08, 2020 at 02:44:12PM -0500, Pierre-Louis Bossart wrote:
> Recent changes in the ASoC core prevent multi-cpu BE dailinks from
> being used. DPCM does support multi-cpu DAIs for BE Dailinks, but not
> for FE.

First I want to apologize for introducing this regression.
Actually when I made the "Only allow playback/capture if supported"
patch I did not realize it would also be used for BE DAIs. :)

> 
> Handle the FE checks first, and make sure all DAIs support the same
> capabilities within the same dailink.
> 
> BugLink: https://github.com/thesofproject/linux/issues/2031
> Fixes: 9b5db059366ae2 ("ASoC: soc-pcm: dpcm: Only allow playback/capture if supported")
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> Reviewed-by: Bard Liao <yung-chuan.liao at linux.intel.com>
> Reviewed-by: Guennadi Liakhovetski <guennadi.liakhovetski at linux.intel.com>
> Reviewed-by: Ranjani Sridharan <ranjani.sridharan at linux.intel.com>
> Reviewed-by: Daniel Baluta <daniel.baluta at gmail.com>
> ---
>  sound/soc/soc-pcm.c | 44 ++++++++++++++++++++++++++++++++++----------
>  1 file changed, 34 insertions(+), 10 deletions(-)
> 
> diff --git a/sound/soc/soc-pcm.c b/sound/soc/soc-pcm.c
> index 276505fb9d50..2c114b4542ce 100644
> --- a/sound/soc/soc-pcm.c
> +++ b/sound/soc/soc-pcm.c
> @@ -2789,20 +2789,44 @@ int soc_new_pcm(struct snd_soc_pcm_runtime *rtd, int num)
>  	struct snd_pcm *pcm;
>  	char new_name[64];
>  	int ret = 0, playback = 0, capture = 0;
> +	int stream;
>  	int i;
>  
> +	if (rtd->dai_link->dynamic && rtd->num_cpus > 1) {
> +		dev_err(rtd->dev,
> +			"DPCM doesn't support Multi CPU for Front-Ends yet\n");
> +		return -EINVAL;
> +	}
> +
>  	if (rtd->dai_link->dynamic || rtd->dai_link->no_pcm) {
> -		cpu_dai = asoc_rtd_to_cpu(rtd, 0);
> -		if (rtd->num_cpus > 1) {
> -			dev_err(rtd->dev,
> -				"DPCM doesn't support Multi CPU yet\n");
> -			return -EINVAL;
> +		if (rtd->dai_link->dpcm_playback) {
> +			stream = SNDRV_PCM_STREAM_PLAYBACK;
> +
> +			for_each_rtd_cpu_dais(rtd, i, cpu_dai)
> +				if (!snd_soc_dai_stream_valid(cpu_dai,
> +							      stream)) {
> +					dev_err(rtd->card->dev,
> +						"CPU DAI %s for rtd %s does not support playback\n",
> +						cpu_dai->name,
> +						rtd->dai_link->stream_name);
> +					return -EINVAL;

Unfortunately the "return -EINVAL" here and below break the case where
dpcm_playback/dpcm_capture does not exactly match the capabilities of
the referenced CPU DAIs. To quote from my commit message:

    At the moment, PCM devices for DPCM are only created based on the
    dpcm_playback/capture parameters of the DAI link, without considering
    if the CPU/FE DAI is actually capable of playback/capture.

    Normally the dpcm_playback/capture parameter should match the
    capabilities of the CPU DAI. However, there is no way to set that
    parameter from the device tree (e.g. with simple-audio-card or
    qcom sound cards). dpcm_playback/capture are always both set to 1.

The basic idea for my commit was to basically stop using
dpcm_playback/capture for the device tree case and infer the
capabilities solely based on referenced DAIs. The DAIs expose if they
are capable of playback/capture, so I see no reason to be required to
duplicate that into the DAI link setup (unless you want to specifically
restrict a DAI link to one direction for some reason...)

With your patch probe now fails with:

   7702000.sound: CPU DAI MultiMedia1 for rtd MultiMedia1 does not support capture

because sound/soc/qcom/common.c sets dpcm_playback = dpcm_capture = 1
even though that FE DAI is currently configured to be playback-only.

I believe Srinivas fixed that problem for the BE DAIs in
commit a2120089251f ("ASoC: qcom: common: set correct directions for dailinks")
(https://lore.kernel.org/alsa-devel/20200612123711.29130-2-srinivas.kandagatla@linaro.org/)

For the QCOM case it may be feasible to set dpcm_playback/dpcm_capture
appropriately because it is basically only used with one particular
DAI driver. But simple-audio-card is generic and used with many
different drivers so hard-coding a call into some other driver like
Srinivas did above won't work in that case.

I wonder if we should downgrade your dev_err(...) to a dev_dbg(...),
and then simply avoid setting playback/capture = 0.
This should fix the case I'm talking about.

What do you think?

Thanks,
Stephan

> +				}
> +			playback = 1;
> +		}
> +		if (rtd->dai_link->dpcm_capture) {
> +			stream = SNDRV_PCM_STREAM_CAPTURE;
> +
> +			for_each_rtd_cpu_dais(rtd, i, cpu_dai)
> +				if (!snd_soc_dai_stream_valid(cpu_dai,
> +							      stream)) {
> +					dev_err(rtd->card->dev,
> +						"CPU DAI %s for rtd %s does not support capture\n",
> +						cpu_dai->name,
> +						rtd->dai_link->stream_name);
> +					return -EINVAL;
> +				}
> +			capture = 1;
>  		}
> -
> -		playback = rtd->dai_link->dpcm_playback &&
> -			   snd_soc_dai_stream_valid(cpu_dai, SNDRV_PCM_STREAM_PLAYBACK);
> -		capture = rtd->dai_link->dpcm_capture &&
> -			  snd_soc_dai_stream_valid(cpu_dai, SNDRV_PCM_STREAM_CAPTURE);
>  	} else {
>  		/* Adapt stream for codec2codec links */
>  		int cpu_capture = rtd->dai_link->params ?
> -- 
> 2.20.1
>