Re: [virtio-dev] Re: [PATCH v2 2/9] ALSA: virtio: add virtio sound driver

[Anton Yakovlev <anton.yakovlev@opensynergy.com>]

Hi Takashi,


On 03.02.2021 17:59, Takashi Iwai wrote:
> On Tue, 02 Feb 2021 00:18:09 +0100,
> Anton Yakovlev wrote:
> > > > +/**
> > > > + * virtsnd_reset_fn() - Kernel worker's function to reset the device.
> > > > + * @work: Reset device work.
> > > > + *
> > > > + * Context: Process context.
> > > > + */
> > > > +static void virtsnd_reset_fn(struct work_struct *work)
> > > > +{
> > > > +     struct virtio_snd *snd =
> > > > +             container_of(work, struct virtio_snd, reset_work);
> > > > +     struct virtio_device *vdev = snd->vdev;
> > > > +     struct device *dev = &vdev->dev;
> > > > +     int rc;
> > > > +
> > > > +     dev_info(dev, "sound device needs reset\n");
> > > > +
> > > > +     /*
> > > > +      * It seems that the only way to properly reset the device is to
> > > > remove
> > > > +      * and re-create the ALSA sound card device.
> > > > +      *
> > > > +      * Also resetting the device involves a number of steps with
> > > > setting the
> > > > +      * status bits described in the virtio specification. And the
> > > > easiest
> > > > +      * way to get everything right is to use the virtio bus interface.
> > > > +      */
> > > > +     rc = dev->bus->remove(dev);
> > > > +     if (rc)
> > > > +             dev_warn(dev, "bus->remove() failed: %d", rc);
> > > > +
> > > > +     rc = dev->bus->probe(dev);
> > > > +     if (rc)
> > > > +             dev_err(dev, "bus->probe() failed: %d", rc);
> > >
> > > This looks very suspicious to me. Wondering what ALSA maintainers
> > will say
> > > to this.
> >
> > I'm also wondering what the virtio people have to say. This part is a
> > purely virtio specific thing. And since none of the existing virtio
> > drivers processes the request to reset the device, it is not clear what
> > is the best way to proceed here. For this reason, the most
> > straightforward and simple solution was chosen.
>
> What is this "reset" actually supposed to do?  Reconfguring
> everything, or changing only certain parameters, devices, whatever?

It means bringing this particular device to its initial state.

After that, the driver can re-read the configurations from the device
and reconfigure everything.


> thanks,
>
> Takashi

--
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin