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

[Dmitry Baryshkov]

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@xxxxxxxxxxx> 
> > 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@xxxxxxxxxxx>
> > > ---
> > >   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