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

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Date:   Wed, 03 Feb 2021 17:59:31 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Anton Yakovlev <anton.yakovlev@...nsynergy.com>
Cc:     Guennadi Liakhovetski <guennadi.liakhovetski@...ux.intel.com>,
        <virtualization@...ts.linux-foundation.org>,
        <alsa-devel@...a-project.org>, <virtio-dev@...ts.oasis-open.org>,
        <linux-kernel@...r.kernel.org>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [virtio-dev] Re: [PATCH v2 2/9] ALSA: virtio: add virtio sound driver

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?


thanks,

Takashi