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    SubjectRe: [PATCH v1 1/3] sound: usb: Add vendor's hooking interface
    On Thu, Mar 24, 2022 at 09:33:40AM +0100, Greg Kroah-Hartman wrote:
    > On Thu, Mar 24, 2022 at 05:10:42PM +0900, Oh Eomji wrote:
    > > In mobile, a co-processor can be used with USB audio to improve power
    > > consumption. To support this type of hardware, hooks need to be added
    > > to the USB audio subsystem to be able to call into the hardware when
    > > needed.
    > >
    > > The main operation of the call-backs are:
    > > - Initialize the co-processor by transmitting data when initializing.
    > > - Change the co-processor setting value through the interface
    > > function.
    > > - Configure sampling rate
    > > - pcm open/close
    > > - other housekeeping
    > >
    > > Known issues:
    > > - This only supports one set of callback hooks, meaning that this only
    > > works if there is one type of USB controller in the system. This
    > > should be changed to be a per-host-controller interface instead of
    > > one global set of callbacks.
    > >
    > > Signed-off-by: JaeHun Jung <jh0801.jung@samsung.com>
    > > Signed-off-by: Oh Eomji <eomji.oh@samsung.com>
    > > ---
    > > sound/usb/card.c | 119 +++++++++++++++++++++++++++++++++++++++++++++++++++
    > > sound/usb/card.h | 20 +++++++++
    > > sound/usb/usbaudio.h | 45 +++++++++++++++++++
    > > 3 files changed, 184 insertions(+)
    > >
    > > diff --git a/sound/usb/card.c b/sound/usb/card.c
    > > index 3769622..bd59311 100644
    > > --- a/sound/usb/card.c
    > > +++ b/sound/usb/card.c
    > > @@ -117,6 +117,117 @@ 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_audio_vendor_ops *usb_vendor_ops;
    > > +
    > > +int snd_vendor_set_ops(struct snd_usb_audio_vendor_ops *ops)
    > > +{
    > > + if ((!ops->connect) ||
    > > + (!ops->disconnect) ||
    > > + (!ops->set_interface) ||
    > > + (!ops->set_rate) ||
    > > + (!ops->set_pcm_buf) ||
    > > + (!ops->set_pcm_intf) ||
    > > + (!ops->set_pcm_connection) ||
    > > + (!ops->set_pcm_binterval) ||
    > > + (!ops->usb_add_ctls))
    > > + return -EINVAL;
    > > +
    > > + usb_vendor_ops = ops;
    > > + return 0;
    > > +}
    > > +EXPORT_SYMBOL_GPL(snd_vendor_set_ops);
    > > +
    > > +struct snd_usb_audio_vendor_ops *snd_vendor_get_ops(void)
    > > +{
    > > + return usb_vendor_ops;
    > > +}
    >
    > This is the function you need to fix up, and add proper reference
    > counting to, in order to solve your "this breaks with multiple USB
    > controllers" problem. So this really should not be all that difficult
    > of a task. Why has it taken years to do so?
    >
    > thanks,
    >
    > greg k-h
    >
    Hi,

    Is that mean the scenario when two or more usb audio devices are
    connected through the hub?

    Thanks,
    Eomji Oh
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