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

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Date: Fri, 9 Feb 2024 13:34:05 -0800
From: Wesley Cheng <quic_wcheng@...cinc.com>
To: Takashi Iwai <tiwai@...e.de>
CC: <srinivas.kandagatla@...aro.org>, <mathias.nyman@...el.com>,
        <perex@...ex.cz>, <conor+dt@...nel.org>, <corbet@....net>,
        <lgirdwood@...il.com>, <andersson@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <gregkh@...uxfoundation.org>,
        <Thinh.Nguyen@...opsys.com>, <broonie@...nel.org>,
        <bgoswami@...cinc.com>, <tiwai@...e.com>, <robh+dt@...nel.org>,
        <konrad.dybcio@...aro.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-sound@...r.kernel.org>,
        <linux-usb@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <alsa-devel@...a-project.org>
Subject: Re: [PATCH v14 32/53] ALSA: usb-audio: Check for support for
 requested audio format

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@...cinc.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