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

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Date:   Sat, 24 Dec 2022 13:03:09 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
Cc:     srinivas.kandagatla@...aro.org, mathias.nyman@...el.com,
        perex@...ex.cz, broonie@...nel.org, lgirdwood@...il.com,
        andersson@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        gregkh@...uxfoundation.org, Thinh.Nguyen@...opsys.com,
        bgoswami@...cinc.com, tiwai@...e.com, robh+dt@...nel.org,
        agross@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
        quic_jackp@...cinc.com, quic_plai@...cinc.com
Subject: Re: [RFC PATCH 04/14] sound: usb: card: Introduce USB SND vendor op callbacks

Hi,

On Sat, 24 Dec 2022 at 01:33, Wesley Cheng <quic_wcheng@...cinc.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@...cinc.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