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

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