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

[Wesley Cheng]

Hi Takashi,

On 2/9/2024 2:42 AM, Takashi Iwai wrote:
> 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@xxxxxxxxxxx>
> > ---
> >   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.

Got it, will remove it.  We also have a dependency in place for the 
qc_audio_offload driver and SND USB AUDIO in the Kconfig.

Thanks
Wesley Cheng