Re: [RFC PATCH 04/14] sound: usb: card: Introduce USB SND vendor op callbacks

Dmitry Baryshkov
2022-12-24T11:03:29Z

Hi,

On Sat, 24 Dec 2022 at 01:33, Wesley Cheng <quic_wcheng@quicinc.com> wrote:
>
> Allow for different vendors to be notified on USB SND connect/disconnect
> seqeunces. This allows for vendor USB SND modules to properly initialize
> and populate internal structures with references to the USB SND chip
> device.

The commit message definitely needs some improvement. We do not notify
vendors on SND connect/disconnect events.

>
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
> sound/usb/card.c | 22 ++++++++++++++++++++++
> sound/usb/card.h | 7 +++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 26268ffb8274..212f55a7683c 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -117,6 +117,21 @@ 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_vendor_ops *vendor_ops;
> +
> +int snd_usb_register_vendor_ops(struct snd_usb_vendor_ops *ops)

platform ops?

> +{
> + vendor_ops = ops;
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_usb_register_vendor_ops);

What happens if several platforms try to register different ops? I saw
from the patch 09/14 that you register these ops unconditionally. If
other devices follow your approach there is an obvious conflict.

> +
> +int snd_usb_unregister_vendor_ops(void)
> +{
> + vendor_ops = NULL;
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(snd_usb_unregister_vendor_ops);
>
> /*
> * disconnect streams
> @@ -910,6 +925,10 @@ static int usb_audio_probe(struct usb_interface *intf,
> usb_set_intfdata(intf, chip);
> atomic_dec(&chip->active);
> mutex_unlock(&register_mutex);
> +
> + if (vendor_ops->connect_cb)
> + vendor_ops->connect_cb(intf, chip);
> +
> return 0;
>
> __error:
> @@ -943,6 +962,9 @@ static void usb_audio_disconnect(struct usb_interface *intf)
> if (chip == USB_AUDIO_IFACE_UNUSED)
> return;
>
> + if (vendor_ops->disconnect_cb)
> + vendor_ops->disconnect_cb(intf);
> +
> card = chip->card;
>
> mutex_lock(&register_mutex);
> diff --git a/sound/usb/card.h b/sound/usb/card.h
> index 40061550105a..a785bb256b0d 100644
> --- a/sound/usb/card.h
> +++ b/sound/usb/card.h
> @@ -206,4 +206,11 @@ struct snd_usb_stream {
> struct list_head list;
> };
>
> +struct snd_usb_vendor_ops {
> + void (*connect_cb)(struct usb_interface *intf, struct snd_usb_audio *chip);
> + void (*disconnect_cb)(struct usb_interface *intf);
> +};
> +
> +int snd_usb_register_vendor_ops(struct snd_usb_vendor_ops *ops);
> +int snd_usb_unregister_vendor_ops(void);
> #endif /* __USBAUDIO_CARD_H */

--
With best wishes

Dmitry