Re: [PATCH v14 32/53] ALSA: usb-audio: Check for support for requested audio format

[Takashi Iwai <tiwai@suse.de>]

On Fri, 09 Feb 2024 00:13:45 +0100,
Wesley Cheng wrote:
> 
> Allow for checks on a specific USB audio device to see if a requested PCM
> format is supported.  This is needed for support when playback is
> initiated by the ASoC USB backend path.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
>  sound/usb/card.c | 31 +++++++++++++++++++++++++++++++
>  sound/usb/card.h | 11 +++++++++++
>  2 files changed, 42 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 7dc8007ba839..1ad99a462038 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -155,6 +155,37 @@ int snd_usb_unregister_platform_ops(void)
>  }
>  EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
>  
> +/*
> + * Checks to see if requested audio profile, i.e sample rate, # of
> + * channels, etc... is supported by the substream associated to the
> + * USB audio device.
> + */
> +struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
> +			struct snd_pcm_hw_params *params, int direction)
> +{
> +	struct snd_usb_audio *chip;
> +	struct snd_usb_substream *subs;
> +	struct snd_usb_stream *as;
> +
> +	/*
> +	 * Register mutex is held when populating and clearing usb_chip
> +	 * array.
> +	 */
> +	guard(mutex)(&register_mutex);
> +	chip = usb_chip[card_idx];
> +
> +	if (chip && enable[card_idx]) {
> +		list_for_each_entry(as, &chip->pcm_list, list) {
> +			subs = &as->substream[direction];
> +			if (snd_usb_find_substream_format(subs, params))
> +				return as;
> +		}
> +	}
> +
> +	return NULL;
> +}
> +EXPORT_SYMBOL_GPL(snd_usb_find_suppported_substream);
> +
>  /*
>   * disconnect streams
>   * called from usb_audio_disconnect()
> diff --git a/sound/usb/card.h b/sound/usb/card.h
> index 02e4ea898db5..ed4a664e24e5 100644
> --- a/sound/usb/card.h
> +++ b/sound/usb/card.h
> @@ -217,4 +217,15 @@ struct snd_usb_platform_ops {
>  
>  int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops);
>  int snd_usb_unregister_platform_ops(void);
> +
> +#if IS_ENABLED(CONFIG_SND_USB_AUDIO)
> +struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
> +			struct snd_pcm_hw_params *params, int direction);
> +#else
> +static struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
> +			struct snd_pcm_hw_params *params, int direction)
> +{
> +	return NULL;
> +}
> +#endif /* IS_ENABLED(CONFIG_SND_USB_AUDIO) */

The usefulness of ifdef guard here is doubtful, IMO.  This header is
only for USB-audio driver enablement, and not seen as generic
helpers.  So, just add the new function declarations without dummy
definitions.


thanks,

Takashi