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

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Date:   Tue, 27 Dec 2022 13:07:05 -0800
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
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 Dmitry,

On 12/24/2022 3:03 AM, Dmitry Baryshkov wrote:
> 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?
> 

Will change it.

>> +{
>> +       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.
> 

Thank you for the review.

That is true.  I don't think there is a proper need to have multiple 
vendor ops being registered, so maybe just returning an error for if ops 
are already registered is sufficient.

Thanks
Wesley Cheng