linux-kernel - Re: [RFC PATCH v2 12/22] sound: usb: card: Introduce USB SND platform op callbacks

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Message-ID: <Y9Ui82OaI54Qx8Ft@kroah.com>
Date:   Sat, 28 Jan 2023 14:28:19 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
Cc:     srinivas.kandagatla@...aro.org, mathias.nyman@...el.com,
        perex@...ex.cz, lgirdwood@...il.com, andersson@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, Thinh.Nguyen@...opsys.com,
        broonie@...nel.org, 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 v2 12/22] sound: usb: card: Introduce USB SND
 platform op callbacks

On Wed, Jan 25, 2023 at 07:14:14PM -0800, 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@...cinc.com>
> ---
>  sound/usb/card.c | 28 ++++++++++++++++++++++++++++
>  sound/usb/card.h | 20 ++++++++++++++++++++
>  2 files changed, 48 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 26268ffb8274..803230343c16 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -117,6 +117,24 @@ 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;

You can not have a single "platform_ops" pointer, this HAS to be
per-bus.

And what is a "platform operations" anyway?  Shouldn't this be a driver
type or something like that?  "offload_operations"?

> +
> +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
> +{
> +	if (platform_ops)
> +		return -EEXIST;
> +
> +	platform_ops = ops;
> +	return 0;

No locking?  not good.

But again, this has to be per-USB-bus, it can NOT be system wide for
obvious reasons.

thanks,

greg k-h