Re: [PATCH v21 33/39] ASoC: usb: Fetch ASoC sound card information

[Wesley Cheng <quic_wcheng@xxxxxxxxxxx>]

Hi Pierre,

On 5/7/2024 2:33 PM, Pierre-Louis Bossart wrote:
> > +/**
> > + * snd_soc_usb_device_offload_available() - Fetch BE DAI link sound card
> > + * @dev: the device to find in SOC USB
> > + *
> > + * Finds the component linked to a specific SOC USB instance, and returns
> > + * the sound card number for the platform card supporting offloading.
> > + *
> > + */
> > +int snd_soc_usb_device_offload_available(struct device *dev)
> > +{
> > +	struct snd_soc_usb *ctx;
> > +
> > +	ctx = snd_soc_find_usb_ctx(dev);
> > +	if (!ctx)
> > +		return -ENODEV;
> > +
> > +	return ctx->component->card->snd_card->number;
> > +}
>
> Presumably there's a notification to help applications discard this
> information on removal?

If the platform/ASoC sound card is removed then the USB BE DAI is going 
to be unregistered from SOC USB.  This would lead to the 
snd_soc_find_usb_ctx() to return with -ENODEV to the USB SND offload 
kcontrol call.

Thanks
Wesley Cheng