Re: [PATCH v9 21/34] ASoC: usb: Add PCM format check API for USB backend

[Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>]

On 10/17/23 15:00, Wesley Cheng wrote:
> Introduce a check for if a particular PCM format is supported by the USB

Introduce a helper to check if a ...

> audio device connected.  If the USB audio device does not have an audio
> profile which can support the requested format, then notify the USB
> backend.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
>  include/sound/soc-usb.h |  3 +++
>  sound/soc/soc-usb.c     | 13 +++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/include/sound/soc-usb.h b/include/sound/soc-usb.h
> index 58c686f4f7ba..c6ddc055c4cd 100644
> --- a/include/sound/soc-usb.h
> +++ b/include/sound/soc-usb.h
> @@ -37,6 +37,9 @@ struct snd_soc_usb {
>  	void *priv_data;
>  };
>  
> +int snd_soc_usb_find_format(int card_idx, struct snd_pcm_hw_params *params,
> +			int direction);
> +
>  int snd_soc_usb_connect(struct device *usbdev, struct snd_soc_usb_device *sdev);
>  int snd_soc_usb_disconnect(struct device *usbdev, struct snd_soc_usb_device *sdev);
>  void *snd_soc_usb_find_priv_data(struct device *usbdev);
> diff --git a/sound/soc/soc-usb.c b/sound/soc/soc-usb.c
> index 73b1bcc3b506..7407678a993e 100644
> --- a/sound/soc/soc-usb.c
> +++ b/sound/soc/soc-usb.c
> @@ -63,6 +63,19 @@ void *snd_soc_usb_find_priv_data(struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(snd_soc_usb_find_priv_data);
>  
> +int snd_soc_usb_find_format(int card_idx, struct snd_pcm_hw_params *params,
> +			int direction)
> +{
> +	struct snd_usb_stream *as;
> +
> +	as = snd_usb_find_suppported_substream(card_idx, params, direction);
> +	if (!as)
> +		return -EOPNOTSUPP;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_soc_usb_find_format);

Is this the right way to check for formats?

formats are defined within the scope of an endpoint, and those endpoints
are themselves defined within the scope of an interface?

I don't see a notion of endpoint here. Does this assume all endpoints
are valid, or maybe the existence of a single endpoint in a device?

Confused.