Re: [PATCH v26 24/33] ALSA: usb-audio: Introduce USB SND platform op callbacks

[Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>]

On 8/29/24 21:40, Wesley Cheng wrote:
> Allow for different platforms to be notified on USB SND connect/disconnect
> sequences.  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@xxxxxxxxxxx>
> ---
>  sound/usb/card.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++
>  sound/usb/card.h | 10 +++++++++
>  2 files changed, 63 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 1f9dfcd8f336..7f120aa006c0 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -118,6 +118,42 @@ 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;
> +
> +/*
> + * Register platform specific operations that will be notified on events
> + * which occur in USB SND.  The platform driver can utilize this path to
> + * enable features, such as USB audio offloading, which allows for audio data
> + * to be queued by an audio DSP.
> + *
> + * Only one set of platform operations can be registered to USB SND.  The
> + * platform register operation is protected by the register_mutex.
> + */
> +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
> +{
> +	guard(mutex)(&register_mutex);
> +	if (platform_ops)
> +		return -EEXIST;
> +
> +	platform_ops = ops;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_usb_register_platform_ops);
> +
> +/*
> + * Unregisters the current set of platform operations.  This allows for

Unregister?

> + * a new set to be registered if required.
> + *
> + * The platform unregister operation is protected by the register_mutex.
> + */
> +int snd_usb_unregister_platform_ops(void)
> +{
> +	guard(mutex)(&register_mutex);
> +	platform_ops = NULL;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
>  
>  /*
>   * Checks to see if requested audio profile, i.e sample rate, # of
> @@ -946,7 +982,11 @@ 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);
> +
>  	return 0;
>  
>   __error:
> @@ -983,6 +1023,9 @@ static void usb_audio_disconnect(struct usb_interface *intf)
>  	card = chip->card;
>  
>  	mutex_lock(&register_mutex);
> +	if (platform_ops && platform_ops->disconnect_cb)
> +		platform_ops->disconnect_cb(chip);
> +
>  	if (atomic_inc_return(&chip->shutdown) == 1) {
>  		struct snd_usb_stream *as;
>  		struct snd_usb_endpoint *ep;
> @@ -1130,6 +1173,11 @@ static int usb_audio_suspend(struct usb_interface *intf, pm_message_t message)
>  		chip->system_suspend = chip->num_suspended_intf;
>  	}
>  
> +	mutex_lock(&register_mutex);
> +	if (platform_ops && platform_ops->suspend_cb)
> +		platform_ops->suspend_cb(intf, message);
> +	mutex_unlock(&register_mutex);
> +
>  	return 0;
>  }
>  
> @@ -1170,6 +1218,11 @@ static int usb_audio_resume(struct usb_interface *intf)
>  
>  	snd_usb_midi_v2_resume_all(chip);
>  
> +	mutex_lock(&register_mutex);
> +	if (platform_ops && platform_ops->resume_cb)
> +		platform_ops->resume_cb(intf);
> +	mutex_unlock(&register_mutex);
> +
>   out:
>  	if (chip->num_suspended_intf == chip->system_suspend) {
>  		snd_power_change_state(chip->card, SNDRV_CTL_POWER_D0);
> diff --git a/sound/usb/card.h b/sound/usb/card.h
> index 4f4f3f39b7fa..23d9e6fc69e7 100644
> --- a/sound/usb/card.h
> +++ b/sound/usb/card.h
> @@ -207,7 +207,17 @@ struct snd_usb_stream {
>  	struct list_head list;
>  };
>  
> +struct snd_usb_platform_ops {
> +	void (*connect_cb)(struct snd_usb_audio *chip);
> +	void (*disconnect_cb)(struct snd_usb_audio *chip);
> +	void (*suspend_cb)(struct usb_interface *intf, pm_message_t message);
> +	void (*resume_cb)(struct usb_interface *intf);
> +};


You're using the same mutex to protect all four callbacks, so how would
things work if e.g. you disconnected a device during the resume operation?