Re: [PATCH 4/4] ASoC: SDCA: class_function: clear sconfig.bps on PDM data-port terminals

[Charles Keepax <ckeepax@opensource.cirrus.com>]

On Sun, Oct 18, 2026 at 08:23:59PM +0100, Srinivas Kandagatla wrote:
> snd_sdw_params_to_config() derives sconfig.bps from the PCM container
> width, which is not meaningful on PDM data-port terminals and clashes
> with masters that declare their own view of the wire word length (e.g.
> the Qualcomm SoundWire master hardcodes sconfig.bps = 1 for PDM).
> 
> Clear sconfig.bps when the DAI's SDCA terminal is PDM so compute_params()
> or the slave silicon drives the per-port wire word length.
> 
> Assisted-by: LLM
> Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@oss.qualcomm.com>
> ---
>  sound/soc/sdca/sdca_class_function.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/sound/soc/sdca/sdca_class_function.c b/sound/soc/sdca/sdca_class_function.c
> index 13b70f0f0dbf..acaadd12432a 100644
> --- a/sound/soc/sdca/sdca_class_function.c
> +++ b/sound/soc/sdca/sdca_class_function.c
> @@ -126,6 +126,17 @@ static int class_function_startup(struct snd_pcm_substream *substream,
>  					 substream, dai);
>  }
>  
> +static bool class_function_terminal_is_pdm(enum sdca_terminal_type t)
> +{
> +	switch (t) {
> +	case SDCA_TERM_TYPE_RAW_PDM_MIC:
> +	case SDCA_TERM_TYPE_PDM_RENDER_STREAM:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}

I think this would make sense as a generic helper in sdca_asoc.c
probably taking the function and the DAI as arguments.

>  static int class_function_sdw_add_peripheral(struct snd_pcm_substream *substream,
>  					     struct snd_pcm_hw_params *params,
>  					     struct snd_soc_dai *dai)
> @@ -133,6 +144,7 @@ static int class_function_sdw_add_peripheral(struct snd_pcm_substream *substream
>  	struct class_function_drv *drv = snd_soc_component_get_drvdata(dai->component);
>  	struct sdw_stream_runtime *sdw_stream = snd_soc_dai_get_dma_data(dai, substream);
>  	struct sdw_slave *sdw = dev_to_sdw_dev(drv->dev->parent);
> +	struct sdca_entity *entity = &drv->function->entities[dai->id];
>  	struct sdw_stream_config sconfig = {0};
>  	struct sdw_port_config pconfig = {0};
>  	int ret;
> @@ -152,6 +164,9 @@ static int class_function_sdw_add_peripheral(struct snd_pcm_substream *substream
>  
>  	pconfig.num = ret;
>  
> +	if (class_function_terminal_is_pdm(entity->iot.type))
> +		sconfig.bps = 0;

I think this is fine, as you say bps makes no sense for a PDM
stream but I might need to spend a little more time working out
how this all propagates through the core. I guess my concern is
if other drivers don't handle PDM in the same way.

Thanks,
Charles