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 23:33:10 +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

On 27/12/2022 23:07, Wesley Cheng wrote:
> 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.

This would be a required step. And also you have to check the running 
platform before registering your ops unconditionally. Ideally this 
should be done as a part of the device's driver, so that we can control 
registration of the platform ops using the usual interface.

> 
> Thanks
> Wesley Cheng

-- 
With best wishes
Dmitry