[v5,11/32] sound: usb: card: Introduce USB SND platform op callbacks

Allow for different platforms to be notified on USB SND connect/disconnect
seqeunces.  This allows for platform USB SND modules to properly initialize
and populate internal structures with references to the USB SND chip
device.

Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
---
 sound/usb/card.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 sound/usb/card.h |  9 +++++++++
 2 files changed, 54 insertions(+)

On Tue, 29 Aug 2023 23:06:36 +0200,
Wesley Cheng wrote:
> 
> Allow for different platforms to be notified on USB SND connect/disconnect
> seqeunces.  This allows for platform USB SND modules to properly initialize
> and populate internal structures with references to the USB SND chip
> device.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
>  sound/usb/card.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  sound/usb/card.h |  9 +++++++++
>  2 files changed, 54 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 1b2edc0fd2e9..067a1e82f4bf 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -118,6 +118,34 @@ MODULE_PARM_DESC(skip_validation, "Skip unit descriptor validation (default: no)
>  static DEFINE_MUTEX(register_mutex);
>  static struct snd_usb_audio *usb_chip[SNDRV_CARDS];
>  static struct usb_driver usb_audio_driver;
> +static struct snd_usb_platform_ops *platform_ops;
> +
> +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
> +{
> +	int ret;
> +
> +	mutex_lock(&register_mutex);
> +	if (platform_ops) {
> +		ret = -EEXIST;
> +		goto out;
> +	}
> +
> +	platform_ops = ops;
> +out:
> +	mutex_unlock(&register_mutex);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_usb_register_platform_ops);

For adding this kind of API, please give the proper comment.
Especially this API is special and need a caution, to mention that it
can be used only for a single instance.

Also, it should be mentioned that all callbacks are exclusive under
the global register_mutex.

> @@ -910,7 +938,11 @@ static int usb_audio_probe(struct usb_interface *intf,
>  	chip->num_interfaces++;
>  	usb_set_intfdata(intf, chip);
>  	atomic_dec(&chip->active);
> +
> +	if (platform_ops && platform_ops->connect_cb)
> +		platform_ops->connect_cb(chip);
>  	mutex_unlock(&register_mutex);

One uncertain thing is the argument for connect_cb and disconnect_cb.
Those take snd_usb_audio object, but the callback gets called per
interface at each probe and disconnect.  How does the callee handle
multiple calls?

Last but not least, the patch subject should be with "ALSA:" prefix,
and in this case, at best "ALSA: usb-audio: xxx".


thanks,

Takashi

Hi Takashi,

On 9/7/2023 8:36 AM, Takashi Iwai wrote:
> On Tue, 29 Aug 2023 23:06:36 +0200,
> Wesley Cheng wrote:
>>
>> Allow for different platforms to be notified on USB SND connect/disconnect
>> seqeunces.  This allows for platform USB SND modules to properly initialize
>> and populate internal structures with references to the USB SND chip
>> device.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
>> ---
>>   sound/usb/card.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>>   sound/usb/card.h |  9 +++++++++
>>   2 files changed, 54 insertions(+)
>>
>> diff --git a/sound/usb/card.c b/sound/usb/card.c
>> index 1b2edc0fd2e9..067a1e82f4bf 100644
>> --- a/sound/usb/card.c
>> +++ b/sound/usb/card.c
>> @@ -118,6 +118,34 @@ MODULE_PARM_DESC(skip_validation, "Skip unit descriptor validation (default: no)
>>   static DEFINE_MUTEX(register_mutex);
>>   static struct snd_usb_audio *usb_chip[SNDRV_CARDS];
>>   static struct usb_driver usb_audio_driver;
>> +static struct snd_usb_platform_ops *platform_ops;
>> +
>> +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
>> +{
>> +	int ret;
>> +
>> +	mutex_lock(&register_mutex);
>> +	if (platform_ops) {
>> +		ret = -EEXIST;
>> +		goto out;
>> +	}
>> +
>> +	platform_ops = ops;
>> +out:
>> +	mutex_unlock(&register_mutex);
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(snd_usb_register_platform_ops);
> 
> For adding this kind of API, please give the proper comment.
> Especially this API is special and need a caution, to mention that it
> can be used only for a single instance.
> 
> Also, it should be mentioned that all callbacks are exclusive under
> the global register_mutex.
> 

Thanks for taking the time to review.  Sure, I'll add some comments in 
these new APIs to document what they are used for and how they are 
protected and limited.

>> @@ -910,7 +938,11 @@ static int usb_audio_probe(struct usb_interface *intf,
>>   	chip->num_interfaces++;
>>   	usb_set_intfdata(intf, chip);
>>   	atomic_dec(&chip->active);
>> +
>> +	if (platform_ops && platform_ops->connect_cb)
>> +		platform_ops->connect_cb(chip);
>>   	mutex_unlock(&register_mutex);
> 
> One uncertain thing is the argument for connect_cb and disconnect_cb.
> Those take snd_usb_audio object, but the callback gets called per
> interface at each probe and disconnect.  How does the callee handle
> multiple calls?

I guess it should depend on how the platform driver wants to handle it? 
  I haven't run into a device with multiple UAC interfaces before, so 
I'll need to mimic this configuration on a device, so I can see how it 
exposes itself.

Will investigate this a bit more on my end and come back with my findings.

> 
> Last but not least, the patch subject should be with "ALSA:" prefix,
> and in this case, at best "ALSA: usb-audio: xxx".
> 
> 

Got it, thanks!

Thanks
Wesley Cheng