ALSA: scarlett2: Default on?

[Takashi Iwai]

On Fri, 25 Jun 2021 04:11:42 +0200,
Geoffrey D. Bennett wrote:
> 
> On Thu, Jun 24, 2021 at 07:40:53PM +0200, Takashi Iwai wrote:
> > On Thu, 24 Jun 2021 17:47:39 +0200,
> > Geoffrey D. Bennett wrote:
> > > 
> > > On Wed, Jun 23, 2021 at 08:39:24AM +0200, Takashi Iwai wrote:
> > > [...]
> > > > OK, now all patches have been merged.
> > > 
> > > Thanks!
> > > 
> > > I would next like to consider how we can enable this mixer driver by
> > > default. I originally added the device_setup=1 gate because there were
> > > reports of the driver making the interface hang. These were all traced
> > > back to the problem which was resolved with the commit "Fix device
> > > hang with ehci-pci". That commit fixed the issue for those who had
> > > reported it and since then there have been no more reports that the
> > > mixer driver causes any issues.
> > > 
> > > Simply removing the device_setup=1 check would leave users with no way
> > > to disable the driver in case that turns out to be necessary for some
> > > reason though, so I don't think that's a good idea.
> > 
> > They can blacklist snd-usb-audio, either the module itself (if it's
> > the only device), or with enable option of snd-usb-audio module, if
> > there are multiple devices bound with the driver.
> 
> But wouldn't that disable audio for the device entirely? I am talking
> about only disabling the mixer part of the driver (the code in
> mixer_scarlett_gen2.c) which uses the proprietary USB messages. So
> that if there is some unseen so-far bug the user can revert to
> previous behaviour of audio working but no proprietary controls.

Even if you split the mixer part to a module, it'll be always bound
with the main snd-usb-audio due to dependency, so you cannot blacklist
it.  At most, you may add a module option for that, but it's almost
equivalent to introduce a new option to snd-usb-audio such as
  snd_usb_audio.scarlett2_mixer=off

A conditional build would make sense for the compilation size, but
it's not about the feature to turn on/off functionality on the fly.


Takashi