linux-kernel - Re: [PATCH v4 11/32] sound: usb: card: Introduce USB SND platform op callbacks

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Message-ID: <87edkwv5sv.wl-tiwai@suse.de>
Date:   Tue, 25 Jul 2023 08:55:28 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
Cc:     <agross@...nel.org>, <andersson@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <catalin.marinas@....com>, <will@...nel.org>,
        <mathias.nyman@...el.com>, <gregkh@...uxfoundation.org>,
        <lgirdwood@...il.com>, <broonie@...nel.org>, <perex@...ex.cz>,
        <tiwai@...e.com>, <srinivas.kandagatla@...aro.org>,
        <bgoswami@...cinc.com>, <Thinh.Nguyen@...opsys.com>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-usb@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <quic_jackp@...cinc.com>, <pierre-louis.bossart@...ux.intel.com>,
        <oneukum@...e.com>, <albertccwang@...gle.com>,
        <o-takashi@...amocchi.jp>
Subject: Re: [PATCH v4 11/32] sound: usb: card: Introduce USB SND platform op callbacks

On Tue, 25 Jul 2023 04:33:55 +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@...cinc.com>
> ---
>  sound/usb/card.c | 36 ++++++++++++++++++++++++++++++++++++
>  sound/usb/card.h | 20 ++++++++++++++++++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index f6e99ced8068..9365d1e17836 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -117,6 +117,30 @@ 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)
> +{
> +	if (platform_ops)
> +		return -EEXIST;
> +	mutex_lock(&register_mutex);
> +	platform_ops = ops;
> +	mutex_unlock(&register_mutex);

The check should be inside register_mutex lock, too.
Otherwise it's racy.


> --- a/sound/usb/card.h
> +++ b/sound/usb/card.h
> @@ -207,4 +207,24 @@ 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);
> +};

Don't we need resume_cb?  Even if it's unused for your platform, it'd
make sense to be a pair.

> +#if IS_ENABLED(CONFIG_SND_USB_AUDIO)
> +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops);
> +int snd_usb_unregister_platform_ops(void);
> +#else
> +static int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static int snd_usb_unregister_platform_ops(void)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#endif /* IS_ENABLED(CONFIG_SND_USB_AUDIO) */

Any need for dummy function definitions?  I thought those exported
functions are always with CONFIG_SND_USB_AUDIO enabled?

IOW, are they use of those functions without USB audio driver?


thanks,

Takashi