diff mbox series

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

Message ID 20240208231406.27397-33-quic_wcheng@quicinc.com
State New
Headers
Series Introduce QC USB SND audio offloading support |

Commit Message

Wesley Cheng Feb. 8, 2024, 11:13 p.m. UTC 
  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(+)

Comments

Takashi Iwai Feb. 9, 2024, 10:42 a.m. UTC | #1 
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
Wesley Cheng Feb. 9, 2024, 9:34 p.m. UTC | #2 
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@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.
> 

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
Wesley Cheng Feb. 16, 2024, 11:42 p.m. UTC | #3 
Hi Takashi,

On 2/9/2024 1:34 PM, Wesley Cheng wrote:
> 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@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.
>>
> 
> 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.
> 

Looking at this again after trying some mixed Kconfig settings.  These 
declarations aren't specific for USB-audio.  They are helpers that are 
exposed to soc usb, so that it can do some basic verification with soc 
usb before allowing the enable stream to continue.  Since the ASoC layer 
doesn't have insight on what audio profiles are supported by the usb 
device, this API will ensure that the request profile is supported.

Issues are seen when we disable SND USB audio config and enable the ASoC 
parts.

Thanks
Wesley Cheng
Takashi Iwai Feb. 17, 2024, 10:08 a.m. UTC | #4 
On Sat, 17 Feb 2024 00:42:18 +0100,
Wesley Cheng wrote:
> 
> Hi Takashi,
> 
> On 2/9/2024 1:34 PM, Wesley Cheng wrote:
> > 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@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.
> >> 
> > 
> > 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.
> > 
> 
> Looking at this again after trying some mixed Kconfig settings.  These
> declarations aren't specific for USB-audio.  They are helpers that are
> exposed to soc usb, so that it can do some basic verification with soc
> usb before allowing the enable stream to continue.

Then rather the question is why snd-soc-usb calls those functions
*unconditionally*.  No matter whether we have dependencies in Kconfig,
calling the function means that the callee shall be drug when the
corresponding code is running.

If it were generic core API stuff such as power-management or ACPI,
it'd make sense to define dummy functions without the enablement, as
many code may have optional calls.  If the API is enabled, it's anyway
in the core.  If not, it's optional.  That'll be fine.

OTOH, the stuff you're calling certainly belongs to snd-usb-audio.
Even if the call is really optional, it means that you'll have a hard
dependency when snd-usb-audio is built, no matter whether you need or
not.

> Since the ASoC
> layer doesn't have insight on what audio profiles are supported by the
> usb device, this API will ensure that the request profile is
> supported.
>
> Issues are seen when we disable SND USB audio config and enable the
> ASoC parts.

If snd-usb-audio is disabled, what snd-soc-usb would serve at all?
Does it still make sense to keep it enabled? 
That said, the statement above (building snd-soc-usb without
snd-usb-audio) looks already dubious; isn't it better to have a proper
dependency in Kconfig, instead?


thanks,

Takashi
Wesley Cheng Feb. 24, 2024, 6:22 a.m. UTC | #5 
Hi Takashi,

On 2/17/2024 2:08 AM, Takashi Iwai wrote:
> On Sat, 17 Feb 2024 00:42:18 +0100,
> Wesley Cheng wrote:
>>
>> Hi Takashi,
>>
>> On 2/9/2024 1:34 PM, Wesley Cheng wrote:
>>> 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@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.
>>>>
>>>
>>> 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.
>>>
>>
>> Looking at this again after trying some mixed Kconfig settings.  These
>> declarations aren't specific for USB-audio.  They are helpers that are
>> exposed to soc usb, so that it can do some basic verification with soc
>> usb before allowing the enable stream to continue.
> 
> Then rather the question is why snd-soc-usb calls those functions
> *unconditionally*.  No matter whether we have dependencies in Kconfig,
> calling the function means that the callee shall be drug when the
> corresponding code is running.
> 
> If it were generic core API stuff such as power-management or ACPI,
> it'd make sense to define dummy functions without the enablement, as
> many code may have optional calls.  If the API is enabled, it's anyway
> in the core.  If not, it's optional.  That'll be fine.
> 
> OTOH, the stuff you're calling certainly belongs to snd-usb-audio.
> Even if the call is really optional, it means that you'll have a hard
> dependency when snd-usb-audio is built, no matter whether you need or
> not.
> 
>> Since the ASoC
>> layer doesn't have insight on what audio profiles are supported by the
>> usb device, this API will ensure that the request profile is
>> supported.
>>
>> Issues are seen when we disable SND USB audio config and enable the
>> ASoC parts.
> 
> If snd-usb-audio is disabled, what snd-soc-usb would serve at all?
> Does it still make sense to keep it enabled?
> That said, the statement above (building snd-soc-usb without
> snd-usb-audio) looks already dubious; isn't it better to have a proper
> dependency in Kconfig, instead?
> 

Ok, took a look at it a bit more and should have gotten all the 
dependencies addressed through Kconfigs.  Thanks for the review comments 
and feedback.

Thanks
Wesley Cheng
diff mbox series

Patch

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) */
 #endif /* __USBAUDIO_CARD_H */