diff mbox series

[V4] ALSA: usb-audio: Scarlett Gen 2 mixer interface

Message ID 20190709132605.GA25293@b4.vu (mailing list archive)
State New, archived
Headers show
Series [V4] ALSA: usb-audio: Scarlett Gen 2 mixer interface | expand

Commit Message

Geoffrey D. Bennett July 9, 2019, 1:26 p.m. UTC
Add mixer quirk for the Focusrite Scarlett 6i6, 18i8, and 18i20 Gen 2
audio interfaces. Although the interfaces are USB compliant,
additional input/output level controls and hardware routing/mixing
functionality are available using proprietary USB requests.

Signed-off-by: Geoffrey D. Bennett <g@b4.vu>
---
Hi all,

This patch adds the following controls for the Scarlett 6i6, 18i8, and
18i20 Gen 2:
- Master volume knob indicator (18i20 only)
- Mute and dim switches (18i20 only)
- Volume controls for the analogue HW outputs
- HW/SW volume switches for the 10 analogue HW outputs (18i20 only)
- Line Level/Instrument Level and Pad controls (6i6 and 18i8 only)
- Output mux (where the sound for the HW outputs comes from; defaults
  to PCM outputs)
- Capture mux (where the sound for PCM recording comes from; defaults
  to HW inputs)
- Matrix mux (where the sound going into the mixer comes from; 18
  inputs default off)
- Mixer matrix (18 inputs * 10 outputs = 180 controls)
- Level meters

Changes since v1:
- Add support for the Scarlett 18i8 Gen 2
- Save configuration parameters to NVRAM
- Implemented feedback from Takashi's email 24/Apr/2019
- Moved private field from struct snd_usb_audio to struct
  usb_mixer_interface
- Added timer and buffer fields to struct usb_mixer_interface
- Other small code fixes/cleanups/improvements

Changes since v2:
- Add support for the Scarlett 6i6 Gen 2
- Add support for controlling the mute/dim switches (18i20 only)
- Implemented feedback from Takashi's email 29/Apr/2019: One pointer
  field private_data and one function pointer private_free. Replaced
  timer with delayed work (thanks for that suggestion; it makes the
  code a *lot* simpler!).
- The new functionality is disabled by default as there were reports
  of some Gen 2 devices not responding to the initialisation sequence
  and hanging. Added module parameter "scarlett_gen2_mixer_enable".
  If this parameter is not set, logs a message "Focusrite Scarlett Gen
  2 Mixer Driver disabled; use options snd_usb_audio
  scarlett_gen2_mixer_enable=1 to enable and report any issues to
  g@b4.vu".

Changes since v3:
- No functional changes; fix checkpatch.pl error and typo in
  declaration.

Only outstanding question I believe:

- Takashi, you wrote last time "Also, the delayed work needs to be
  canceled or flushed at PM suspend callback as well as
  disconnecting." I'm not sure why it should be cancelled; is it not
  okay to do on resume? But I tested suspending while the delayed work
  was waiting and it seemed like the delayed work was cancelled
  anyway. Probably better to do a flush on suspend though; should this
  be done through a hook like:

  diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
  index 2444737a14b2..1572a89267c6 100644
  --- a/sound/usb/mixer.c
  +++ b/sound/usb/mixer.c
  @@ -3547,6 +3547,8 @@ static int snd_usb_mixer_activate(struct usb_mixer_interface *mixer)
   int snd_usb_mixer_suspend(struct usb_mixer_interface *mixer)
   {
          snd_usb_mixer_inactivate(mixer);
  +       if (mixer->private_suspend)
  +               mixer->private_suspend(mixer);
          return 0;
   }
   
  diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
  index fa6e216a06f0..d94c688c65f7 100644
  --- a/sound/usb/mixer.h
  +++ b/sound/usb/mixer.h
  @@ -28,6 +28,7 @@ struct usb_mixer_interface {
   
          void *private_data;
          void (*private_free)(struct usb_mixer_interface *private_data);
  +       void (*private_suspend)(struct usb_mixer_interface *);
   };
   
   #define MAX_CHANNELS   16      /* max logical channels */

  ...or just keep the existing behaviour where it seems to get
  cancelled?

Thanks,
Geoffrey.

Comments

Takashi Iwai July 9, 2019, 1:57 p.m. UTC | #1
On Tue, 09 Jul 2019 15:26:05 +0200,
Geoffrey D. Bennett wrote:
> 
> Only outstanding question I believe:
> 
> - Takashi, you wrote last time "Also, the delayed work needs to be
>   canceled or flushed at PM suspend callback as well as
>   disconnecting." I'm not sure why it should be cancelled; is it not
>   okay to do on resume?

Not really.  The standard idiom is to cancel the pending task
immediately at suspend, so that the whole PM procedure won't be
interfered, then reschedule the work at resume again.

> But I tested suspending while the delayed work
>   was waiting and it seemed like the delayed work was cancelled
>   anyway. Probably better to do a flush on suspend though;

The flush would block, hence it wastes lots of time at suspend.
Ideally the suspend should be performed immediately.

> should this
>   be done through a hook like:
> 
>   diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
>   index 2444737a14b2..1572a89267c6 100644
>   --- a/sound/usb/mixer.c
>   +++ b/sound/usb/mixer.c
>   @@ -3547,6 +3547,8 @@ static int snd_usb_mixer_activate(struct usb_mixer_interface *mixer)
>    int snd_usb_mixer_suspend(struct usb_mixer_interface *mixer)
>    {
>           snd_usb_mixer_inactivate(mixer);
>   +       if (mixer->private_suspend)
>   +               mixer->private_suspend(mixer);
>           return 0;
>    }
>    
>   diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
>   index fa6e216a06f0..d94c688c65f7 100644
>   --- a/sound/usb/mixer.h
>   +++ b/sound/usb/mixer.h
>   @@ -28,6 +28,7 @@ struct usb_mixer_interface {
>    
>           void *private_data;
>           void (*private_free)(struct usb_mixer_interface *private_data);
>   +       void (*private_suspend)(struct usb_mixer_interface *);
>    };
>    
>    #define MAX_CHANNELS   16      /* max logical channels */
> 
>   ...or just keep the existing behaviour where it seems to get
>   cancelled?

I'm fine to add the new suspend/resume callbacks, but maybe the
corresponding resume would be needed.

Other than that, the patch looks almost good.

> --- /dev/null
> +++ b/sound/usb/mixer_scarlett_gen2.c
> @@ -0,0 +1,2078 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + *   Focusrite Scarlett 6i6/18i8/18i20 Gen 2 Driver for ALSA
> + *
> + *   Copyright (c) 2018-2019 by Geoffrey D. Bennett <g at b4.vu>
> + *
> + *   Based on the Scarlett (Gen 1) Driver for ALSA:
> + *
> + *   Copyright (c) 2013 by Tobias Hoffmann
> + *   Copyright (c) 2013 by Robin Gareus <robin at gareus.org>
> + *   Copyright (c) 2002 by Takashi Iwai <tiwai at suse.de>
> + *   Copyright (c) 2014 by Chris J Arges <chris.j.arges at canonical.com>
> + *
> + *   Many codes borrowed from audio.c by
> + *     Alan Cox (alan at lxorguk.ukuu.org.uk)
> + *     Thomas Sailer (sailer at ife.ee.ethz.ch)
> + *
> + *   Code cleanup:
> + *   David Henningsson <david.henningsson at canonical.com>
> + *
> + *   This program is free software; you can redistribute it and/or modify
> + *   it under the terms of the GNU General Public License as published by
> + *   the Free Software Foundation; either version 2 of the License, or
> + *   (at your option) any later version.
> + *
> + *   This program is distributed in the hope that it will be useful,
> + *   but WITHOUT ANY WARRANTY; without even the implied warranty of
> + *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + *   GNU General Public License for more details.

Drop these texts.  The SPDX identifier should suffice.

> +static int scarlett_gen2_mixer_enable;
> +module_param(scarlett_gen2_mixer_enable, int, 0444);
> +MODULE_PARM_DESC(scarlett_gen2_mixer_enable,
> +		 "Focusrite Scarlett Gen 2 Mixer Driver Enable");

Do we need this?  If disabling the quirk is really required, it should
be implemented rather in a generic option, instead.


> +/* Send a proprietary format request to the Scarlett interface */
> +static int scarlett2_usb(
> +	struct usb_mixer_interface *mixer, u32 cmd,
> +	void *req_data, u16 req_size, void *resp_data, u16 resp_size)
> +{
> +	struct scarlett2_mixer_data *private = mixer->private_data;
> +
> +	u16 req_buf_size = sizeof(struct scarlett2_usb_packet) + req_size;
> +	u16 resp_buf_size = sizeof(struct scarlett2_usb_packet) + resp_size;
> +
> +	struct scarlett2_usb_packet *req = 0, *resp = 0;
> +
> +	int err = 0;

Avoid unnecessary blank lines.

> +
> +	mutex_lock(&private->usb_mutex);
> +
> +	/* build request message and send it */
> +
> +	req = kmalloc(req_buf_size, GFP_KERNEL);
> +	if (!req) {
> +		err = -ENOMEM;
> +		goto unlock;
> +	}

Better to run kmalloc outside the mutex.  It's not necessarily
exclusive.

> +	/* send a second message to get the response */
> +
> +	resp = kmalloc(resp_buf_size, GFP_KERNEL);
> +	if (!resp) {
> +		err = -ENOMEM;
> +		goto unlock;
> +	}

Ditto, this could be better allocated before the critical section.


thanks,

Takashi
Geoffrey D. Bennett July 9, 2019, 4:24 p.m. UTC | #2
On Tue, Jul 09, 2019 at 03:57:28PM +0200, Takashi Iwai wrote:
[...]
> > But I tested suspending while the delayed work
> >   was waiting and it seemed like the delayed work was cancelled
> >   anyway. Probably better to do a flush on suspend though;
> 
> The flush would block, hence it wastes lots of time at suspend.
> Ideally the suspend should be performed immediately.
> 
> > should this
> >   be done through a hook like:
> > 
> >   diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> >   index 2444737a14b2..1572a89267c6 100644
> >   --- a/sound/usb/mixer.c
> >   +++ b/sound/usb/mixer.c
> >   @@ -3547,6 +3547,8 @@ static int snd_usb_mixer_activate(struct usb_mixer_interface *mixer)
> >    int snd_usb_mixer_suspend(struct usb_mixer_interface *mixer)
> >    {
> >           snd_usb_mixer_inactivate(mixer);
> >   +       if (mixer->private_suspend)
> >   +               mixer->private_suspend(mixer);
> >           return 0;
> >    }
> >    
> >   diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
> >   index fa6e216a06f0..d94c688c65f7 100644
> >   --- a/sound/usb/mixer.h
> >   +++ b/sound/usb/mixer.h
> >   @@ -28,6 +28,7 @@ struct usb_mixer_interface {
> >    
> >           void *private_data;
> >           void (*private_free)(struct usb_mixer_interface *private_data);
> >   +       void (*private_suspend)(struct usb_mixer_interface *);
> >    };
> >    
> >    #define MAX_CHANNELS   16      /* max logical channels */
> > 
> >   ...or just keep the existing behaviour where it seems to get
> >   cancelled?
> 
> I'm fine to add the new suspend/resume callbacks, but maybe the
> corresponding resume would be needed.

Did you mean "wouldn't be needed"?

[...]
> > +static int scarlett_gen2_mixer_enable;
> > +module_param(scarlett_gen2_mixer_enable, int, 0444);
> > +MODULE_PARM_DESC(scarlett_gen2_mixer_enable,
> > +		 "Focusrite Scarlett Gen 2 Mixer Driver Enable");
> 
> Do we need this?  If disabling the quirk is really required, it should
> be implemented rather in a generic option, instead.

Actually it would be best to have it disabled by default as I have had
two reports from people who tried this mixer driver and it broke audio
for them.

The failure looks like this... the first vendor-specific USB message
sent to the interface to initialise it results in an error:

e2d87480 3146602314 S Ci:1:007:0 s a1 03 0000 0005 0010 16 <
e2d87480 3152107418 C Ci:1:007:0 -2 0

My mixer driver gives up initialising, and subsequent USB messages
fail:

e2d87480 3152110424 S Ci:1:007:0 s 80 06 0304 0409 00ff 255 <
e2d87480 3152121815 C Ci:1:007:0 -71 0
e2d87480 3152121955 S Ci:1:007:0 s 80 06 0304 0409 0002 2 <
e2d87480 3152131554 C Ci:1:007:0 -71 0
e2d87480 3152133420 S Ci:1:007:0 s 80 06 0305 0409 00ff 255 <
e2d87480 3157224469 C Ci:1:007:0 -2 0

I don't see any way to distinguish between devices that do and don't
work before sending the initialisation message. lsusb -v output is
identical. I need someone to do a USB capture to see what the vendor
driver does differently, but I haven't found someone who can do this
yet.

I have 9 success reports so far and 2 failure reports. I hope that by
getting this driver out to a wider audience I can get the data I need
to make it work in all cases and then we can remove the
scarlett_gen2_mixer_enable quirk and have the driver always enabled.

Thanks for your feedback again. The other things which I didn't
comment on I agree with and will fix.

Regards,
Geoffrey.
Takashi Iwai July 9, 2019, 5:14 p.m. UTC | #3
On Tue, 09 Jul 2019 18:24:30 +0200,
Geoffrey D. Bennett wrote:
> 
> On Tue, Jul 09, 2019 at 03:57:28PM +0200, Takashi Iwai wrote:
> [...]
> > > But I tested suspending while the delayed work
> > >   was waiting and it seemed like the delayed work was cancelled
> > >   anyway. Probably better to do a flush on suspend though;
> > 
> > The flush would block, hence it wastes lots of time at suspend.
> > Ideally the suspend should be performed immediately.
> > 
> > > should this
> > >   be done through a hook like:
> > > 
> > >   diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
> > >   index 2444737a14b2..1572a89267c6 100644
> > >   --- a/sound/usb/mixer.c
> > >   +++ b/sound/usb/mixer.c
> > >   @@ -3547,6 +3547,8 @@ static int snd_usb_mixer_activate(struct usb_mixer_interface *mixer)
> > >    int snd_usb_mixer_suspend(struct usb_mixer_interface *mixer)
> > >    {
> > >           snd_usb_mixer_inactivate(mixer);
> > >   +       if (mixer->private_suspend)
> > >   +               mixer->private_suspend(mixer);
> > >           return 0;
> > >    }
> > >    
> > >   diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
> > >   index fa6e216a06f0..d94c688c65f7 100644
> > >   --- a/sound/usb/mixer.h
> > >   +++ b/sound/usb/mixer.h
> > >   @@ -28,6 +28,7 @@ struct usb_mixer_interface {
> > >    
> > >           void *private_data;
> > >           void (*private_free)(struct usb_mixer_interface *private_data);
> > >   +       void (*private_suspend)(struct usb_mixer_interface *);
> > >    };
> > >    
> > >    #define MAX_CHANNELS   16      /* max logical channels */
> > > 
> > >   ...or just keep the existing behaviour where it seems to get
> > >   cancelled?
> > 
> > I'm fine to add the new suspend/resume callbacks, but maybe the
> > corresponding resume would be needed.
> 
> Did you mean "wouldn't be needed"?

No, it's needed because at resume you'd reschedule the work that was
canceled at suspend.  It's specific.

> [...]
> > > +static int scarlett_gen2_mixer_enable;
> > > +module_param(scarlett_gen2_mixer_enable, int, 0444);
> > > +MODULE_PARM_DESC(scarlett_gen2_mixer_enable,
> > > +		 "Focusrite Scarlett Gen 2 Mixer Driver Enable");
> > 
> > Do we need this?  If disabling the quirk is really required, it should
> > be implemented rather in a generic option, instead.
> 
> Actually it would be best to have it disabled by default as I have had
> two reports from people who tried this mixer driver and it broke audio
> for them.

Hm, and these have the same USB device ID?

> The failure looks like this... the first vendor-specific USB message
> sent to the interface to initialise it results in an error:
> 
> e2d87480 3146602314 S Ci:1:007:0 s a1 03 0000 0005 0010 16 <
> e2d87480 3152107418 C Ci:1:007:0 -2 0
> 
> My mixer driver gives up initialising, and subsequent USB messages
> fail:
> 
> e2d87480 3152110424 S Ci:1:007:0 s 80 06 0304 0409 00ff 255 <
> e2d87480 3152121815 C Ci:1:007:0 -71 0
> e2d87480 3152121955 S Ci:1:007:0 s 80 06 0304 0409 0002 2 <
> e2d87480 3152131554 C Ci:1:007:0 -71 0
> e2d87480 3152133420 S Ci:1:007:0 s 80 06 0305 0409 00ff 255 <
> e2d87480 3157224469 C Ci:1:007:0 -2 0
> 
> I don't see any way to distinguish between devices that do and don't
> work before sending the initialisation message. lsusb -v output is
> identical. I need someone to do a USB capture to see what the vendor
> driver does differently, but I haven't found someone who can do this
> yet.
> 
> I have 9 success reports so far and 2 failure reports. I hope that by
> getting this driver out to a wider audience I can get the data I need
> to make it work in all cases and then we can remove the
> scarlett_gen2_mixer_enable quirk and have the driver always enabled.
> 
> Thanks for your feedback again. The other things which I didn't
> comment on I agree with and will fix.

I guess you can use chip->setup value for the quirk-specific
configuration as a start.  It's a bit hackish but the parameter is
already there for long time, hence you don't need to add any extra
stuff for that.


thanks,

Takashi
Geoffrey D. Bennett July 10, 2019, 2:06 p.m. UTC | #4
On Tue, Jul 09, 2019 at 07:14:15PM +0200, Takashi Iwai wrote:
> On Tue, 09 Jul 2019 18:24:30 +0200,
> Geoffrey D. Bennett wrote:
[...]
> > > > +static int scarlett_gen2_mixer_enable;
> > > > +module_param(scarlett_gen2_mixer_enable, int, 0444);
> > > > +MODULE_PARM_DESC(scarlett_gen2_mixer_enable,
> > > > +		 "Focusrite Scarlett Gen 2 Mixer Driver Enable");
> > > 
> > > Do we need this?  If disabling the quirk is really required, it should
> > > be implemented rather in a generic option, instead.
> > 
> > Actually it would be best to have it disabled by default as I have had
> > two reports from people who tried this mixer driver and it broke audio
> > for them.
> 
> Hm, and these have the same USB device ID?

Yes, same device ID. I couldn't see any significant difference between
mine and theirs usbmon trace and lsusb -v output.

[...]
> I guess you can use chip->setup value for the quirk-specific
> configuration as a start.  It's a bit hackish but the parameter is
> already there for long time, hence you don't need to add any extra
> stuff for that.

Got it. Have implemented and will resend soon.

In your other email you wrote:

> Canceling the pending work is the right thing for suspend, but we need
> reconsidering the side effect.  For example, the device might be
> removed while the machine is in sleep.  And the purpose of the
> scheduled work is to sync the config to NVRAM.  That is, it should
> have been done before going to suspend.  Then we don't have to resume
> the task at resume, too.
> 
> That said, the best would be:
> - cancel the pending work, check the return value
> - re-execute the work immediately (delay=0) if the work was canceled
>   in the above, and do flush -- or just call the function directly

I agree and have implemented that as well.

Thanks,
Geoffrey.
diff mbox series

Patch

diff --git a/sound/usb/Makefile b/sound/usb/Makefile
index e1ce257ab705..f4b7384caa9d 100644
--- a/sound/usb/Makefile
+++ b/sound/usb/Makefile
@@ -11,6 +11,7 @@  snd-usb-audio-objs := 	card.o \
 			mixer.o \
 			mixer_quirks.o \
 			mixer_scarlett.o \
+			mixer_scarlett_gen2.o \
 			mixer_us16x08.o \
 			pcm.o \
 			power.o \
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index c703f8534b07..079ebb85805f 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -3505,6 +3505,8 @@  void snd_usb_mixer_disconnect(struct usb_mixer_interface *mixer)
 		usb_kill_urb(mixer->urb);
 	if (mixer->rc_urb)
 		usb_kill_urb(mixer->rc_urb);
+	if (mixer->private_free)
+		mixer->private_free(mixer);
 	mixer->disconnected = true;
 }
 
diff --git a/sound/usb/mixer.h b/sound/usb/mixer.h
index 394cd9107507..41e8be671b73 100644
--- a/sound/usb/mixer.h
+++ b/sound/usb/mixer.h
@@ -28,6 +28,9 @@  struct usb_mixer_interface {
 	struct media_mixer_ctl *media_mixer_ctl;
 
 	bool disconnected;
+
+	void *private_data;
+	void (*private_free)(struct usb_mixer_interface *mixer);
 };
 
 #define MAX_CHANNELS	16	/* max logical channels */
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index 199fa157a411..70805c15b0b5 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -32,6 +32,7 @@ 
 #include "mixer.h"
 #include "mixer_quirks.h"
 #include "mixer_scarlett.h"
+#include "mixer_scarlett_gen2.h"
 #include "mixer_us16x08.h"
 #include "helper.h"
 
@@ -2258,6 +2259,12 @@  int snd_usb_mixer_apply_create_quirk(struct usb_mixer_interface *mixer)
 		err = snd_scarlett_controls_create(mixer);
 		break;
 
+	case USB_ID(0x1235, 0x8203): /* Focusrite Scarlett 6i6 2nd Gen */
+	case USB_ID(0x1235, 0x8204): /* Focusrite Scarlett 18i8 2nd Gen */
+	case USB_ID(0x1235, 0x8201): /* Focusrite Scarlett 18i20 2nd Gen */
+		err = snd_scarlett_gen2_controls_create(mixer);
+		break;
+
 	case USB_ID(0x041e, 0x323b): /* Creative Sound Blaster E1 */
 		err = snd_soundblaster_e1_switch_create(mixer);
 		break;
diff --git a/sound/usb/mixer_scarlett_gen2.c b/sound/usb/mixer_scarlett_gen2.c
new file mode 100644
index 000000000000..02bab6ae59e8
--- /dev/null
+++ b/sound/usb/mixer_scarlett_gen2.c
@@ -0,0 +1,2078 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *   Focusrite Scarlett 6i6/18i8/18i20 Gen 2 Driver for ALSA
+ *
+ *   Copyright (c) 2018-2019 by Geoffrey D. Bennett <g at b4.vu>
+ *
+ *   Based on the Scarlett (Gen 1) Driver for ALSA:
+ *
+ *   Copyright (c) 2013 by Tobias Hoffmann
+ *   Copyright (c) 2013 by Robin Gareus <robin at gareus.org>
+ *   Copyright (c) 2002 by Takashi Iwai <tiwai at suse.de>
+ *   Copyright (c) 2014 by Chris J Arges <chris.j.arges at canonical.com>
+ *
+ *   Many codes borrowed from audio.c by
+ *     Alan Cox (alan at lxorguk.ukuu.org.uk)
+ *     Thomas Sailer (sailer at ife.ee.ethz.ch)
+ *
+ *   Code cleanup:
+ *   David Henningsson <david.henningsson at canonical.com>
+ *
+ *   This program is free software; you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *   GNU General Public License for more details.
+ *
+ */
+
+/* Mixer Interface for the Focusrite Scarlett 6i6/18i8/18i20 Gen 2 audio
+ * interface. Based on the Gen 1 driver and rewritten.
+ */
+
+/* The protocol was reverse engineered by looking at the communication
+ * between Focusrite Control 2.3.4 and the Focusrite(R) Scarlett 18i20
+ * (firmware 1083) using usbmon in July-August 2018.
+ *
+ * Scarlett 18i8 support added in April 2019.
+ *
+ * Scarlett 6i6 support added in June 2019 (thanks to Martin Wittmann
+ * for providing usbmon output and testing).
+ *
+ * This ALSA mixer gives access to:
+ *  - input, output, mixer-matrix muxes
+ *  - 18x10 mixer-matrix gain stages
+ *  - gain/volume controls
+ *  - level meters
+ *  - line/inst level and pad controls
+ *
+ * <ditaa>
+ *    /--------------\    18chn            20chn     /--------------\
+ *    | Hardware  in +--+------\    /-------------+--+ ALSA PCM out |
+ *    \--------------/  |      |    |             |  \--------------/
+ *                      |      |    |    /-----\  |
+ *                      |      |    |    |     |  |
+ *                      |      v    v    v     |  |
+ *                      |   +---------------+  |  |
+ *                      |    \ Matrix  Mux /   |  |
+ *                      |     +-----+-----+    |  |
+ *                      |           |          |  |
+ *                      |           |18chn     |  |
+ *                      |           |          |  |
+ *                      |           |     10chn|  |
+ *                      |           v          |  |
+ *                      |     +------------+   |  |
+ *                      |     | Mixer      |   |  |
+ *                      |     |     Matrix |   |  |
+ *                      |     |            |   |  |
+ *                      |     | 18x10 Gain |   |  |
+ *                      |     |   stages   |   |  |
+ *                      |     +-----+------+   |  |
+ *                      |           |          |  |
+ *                      |18chn      |10chn     |  |20chn
+ *                      |           |          |  |
+ *                      |           +----------/  |
+ *                      |           |             |
+ *                      v           v             v
+ *                      ===========================
+ *               +---------------+       +--—------------+
+ *                \ Output  Mux /         \ Capture Mux /
+ *                 +---+---+---+           +-----+-----+
+ *                     |   |                     |
+ *                10chn|   |                     |18chn
+ *                     |   |                     |
+ *  /--------------\   |   |                     |   /--------------\
+ *  | S/PDIF, ADAT |<--/   |10chn                \-->| ALSA PCM in  |
+ *  | Hardware out |       |                         \--------------/
+ *  \--------------/       |
+ *                         v
+ *                  +-------------+    Software gain per channel.
+ *                  | Master Gain |<-- 18i20 only: Switch per channel
+ *                  +------+------+    to select HW or SW gain control.
+ *                         |
+ *                         |10chn
+ *  /--------------\       |
+ *  | Analogue     |<------/
+ *  | Hardware out |
+ *  \--------------/
+ * </ditaa>
+ *
+ */
+
+#include <linux/slab.h>
+#include <linux/usb.h>
+#include <linux/moduleparam.h>
+
+#include <sound/control.h>
+#include <sound/tlv.h>
+
+#include "usbaudio.h"
+#include "mixer.h"
+#include "helper.h"
+
+#include "mixer_scarlett_gen2.h"
+
+static int scarlett_gen2_mixer_enable;
+module_param(scarlett_gen2_mixer_enable, int, 0444);
+MODULE_PARM_DESC(scarlett_gen2_mixer_enable,
+		 "Focusrite Scarlett Gen 2 Mixer Driver Enable");
+
+/* some gui mixers can't handle negative ctl values */
+#define SCARLETT_VOLUME_BIAS 127
+
+/* mixer range from -80dB to +6dB in 0.5dB steps */
+#define SCARLETT_MIXER_MIN_DB -80
+#define SCARLETT_MIXER_BIAS (-SCARLETT_MIXER_MIN_DB * 2)
+#define SCARLETT_MIXER_MAX_DB 6
+#define SCARLETT_MIXER_MAX_VALUE \
+	((SCARLETT_MIXER_MAX_DB - SCARLETT_MIXER_MIN_DB) * 2)
+
+/* map from (dB + 80) * 2 to mixer value
+ * for dB in 0 .. 172: int(8192 * pow(10, ((dB - 160) / 2 / 20)))
+ */
+static const u16 scarlett2_mixer_values[173] = {
+	0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2,
+	2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 8, 8,
+	9, 9, 10, 10, 11, 12, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,
+	23, 24, 25, 27, 29, 30, 32, 34, 36, 38, 41, 43, 46, 48, 51,
+	54, 57, 61, 65, 68, 73, 77, 81, 86, 91, 97, 103, 109, 115,
+	122, 129, 137, 145, 154, 163, 173, 183, 194, 205, 217, 230,
+	244, 259, 274, 290, 307, 326, 345, 365, 387, 410, 434, 460,
+	487, 516, 547, 579, 614, 650, 689, 730, 773, 819, 867, 919,
+	973, 1031, 1092, 1157, 1225, 1298, 1375, 1456, 1543, 1634,
+	1731, 1833, 1942, 2057, 2179, 2308, 2445, 2590, 2744, 2906,
+	3078, 3261, 3454, 3659, 3876, 4105, 4349, 4606, 4879, 5168,
+	5475, 5799, 6143, 6507, 6892, 7301, 7733, 8192, 8677, 9191,
+	9736, 10313, 10924, 11571, 12257, 12983, 13752, 14567, 15430,
+	16345
+};
+
+/* Maximum number of analogue outputs */
+#define SCARLETT2_ANALOGUE_MAX 10
+
+/* Maximum number of level and pad switches */
+#define SCARLETT2_LEVEL_SWITCH_MAX 2
+#define SCARLETT2_PAD_SWITCH_MAX 4
+
+/* Maximum number of inputs to the mixer */
+#define SCARLETT2_INPUT_MIX_MAX 18
+
+/* Maximum number of outputs from the mixer */
+#define SCARLETT2_OUTPUT_MIX_MAX 10
+
+/* Maximum size of the data in the USB mux assignment message:
+ * 18 inputs, 20 outputs, 18 matrix inputs, 8 spare
+ */
+#define SCARLETT2_MUX_MAX 64
+
+/* Number of meters:
+ * 18 inputs, 20 outputs, 18 matrix inputs
+ */
+#define SCARLETT2_NUM_METERS 56
+
+/* Hardware port types:
+ * - None (no input to mux)
+ * - Analogue I/O
+ * - S/PDIF I/O
+ * - ADAT I/O
+ * - Mixer I/O
+ * - PCM I/O
+ */
+enum {
+	SCARLETT2_PORT_TYPE_NONE = 0,
+	SCARLETT2_PORT_TYPE_ANALOGUE = 1,
+	SCARLETT2_PORT_TYPE_SPDIF = 2,
+	SCARLETT2_PORT_TYPE_ADAT = 3,
+	SCARLETT2_PORT_TYPE_MIX = 4,
+	SCARLETT2_PORT_TYPE_PCM = 5,
+	SCARLETT2_PORT_TYPE_COUNT = 6,
+};
+
+/* Count of total I/O and number available at each sample rate */
+enum {
+	SCARLETT2_PORT_IN = 0,
+	SCARLETT2_PORT_OUT = 1,
+	SCARLETT2_PORT_OUT_44 = 2,
+	SCARLETT2_PORT_OUT_88 = 3,
+	SCARLETT2_PORT_OUT_176 = 4,
+	SCARLETT2_PORT_DIRECTIONS = 5,
+};
+
+/* Hardware buttons on the 18i20 */
+#define SCARLETT2_BUTTON_MAX 2
+
+static const char *const scarlett2_button_names[SCARLETT2_BUTTON_MAX] = {
+	"Mute", "Dim"
+};
+
+/* Description of each hardware port type:
+ * - id: hardware ID for this port type
+ * - num: number of sources/destinations of this port type
+ * - src_descr: printf format string for mux input selections
+ * - src_num_offset: added to channel number for the fprintf
+ * - dst_descr: printf format string for mixer controls
+ */
+struct scarlett2_ports {
+	u16 id;
+	int num[SCARLETT2_PORT_DIRECTIONS];
+	const char * const src_descr;
+	int src_num_offset;
+	const char * const dst_descr;
+};
+
+struct scarlett2_device_info {
+	u8 line_out_hw_vol; /* line out hw volume is sw controlled */
+	u8 button_count; /* number of buttons */
+	u8 level_input_count; /* inputs with level selectable */
+	u8 pad_input_count; /* inputs with pad selectable */
+	const char * const line_out_descrs[SCARLETT2_ANALOGUE_MAX];
+	struct scarlett2_ports ports[SCARLETT2_PORT_TYPE_COUNT];
+};
+
+struct scarlett2_mixer_data {
+	struct usb_mixer_interface *mixer;
+	struct mutex usb_mutex; /* prevent sending concurrent USB requests */
+	struct mutex data_mutex; /* lock access to this data */
+	struct delayed_work work;
+	const struct scarlett2_device_info *info;
+	int num_mux_srcs;
+	u16 scarlett2_seq;
+	u8 vol_updated;
+	u8 master_vol;
+	u8 vol[SCARLETT2_ANALOGUE_MAX];
+	u8 vol_sw_hw_switch[SCARLETT2_ANALOGUE_MAX];
+	u8 level_switch[SCARLETT2_LEVEL_SWITCH_MAX];
+	u8 pad_switch[SCARLETT2_PAD_SWITCH_MAX];
+	u8 buttons[SCARLETT2_BUTTON_MAX];
+	struct snd_kcontrol *master_vol_ctl;
+	struct snd_kcontrol *vol_ctls[SCARLETT2_ANALOGUE_MAX];
+	struct snd_kcontrol *button_ctls[SCARLETT2_BUTTON_MAX];
+	u8 mux[SCARLETT2_MUX_MAX];
+	u8 mix[SCARLETT2_INPUT_MIX_MAX * SCARLETT2_OUTPUT_MIX_MAX];
+};
+
+static void snd_scarlett_gen2_private_free(struct usb_mixer_interface *mixer);
+
+/*** Model-specific data ***/
+
+static const struct scarlett2_device_info s6i6_gen2_info = {
+	/* The first two analogue inputs can be switched between line
+	 * and instrument levels.
+	 */
+	.level_input_count = 2,
+
+	/* The first two analogue inputs have an optional pad. */
+	.pad_input_count = 2,
+
+	.line_out_descrs = {
+		"Monitor L",
+		"Monitor R",
+		"Headphones L",
+		"Headphones R",
+	},
+
+	.ports = {
+		{
+			.id = 0x000,
+			.num = { 1, 0, 8, 8, 8 },
+			.src_descr = "Off",
+			.src_num_offset = 0,
+		},
+		{
+			.id = 0x080,
+			.num = { 4, 4, 4, 4, 4 },
+			.src_descr = "Analogue %d",
+			.src_num_offset = 1,
+			.dst_descr = "Analogue Output %02d Playback"
+		},
+		{
+			.id = 0x180,
+			.num = { 2, 2, 2, 2, 2 },
+			.src_descr = "S/PDIF %d",
+			.src_num_offset = 1,
+			.dst_descr = "S/PDIF Output %d Playback"
+		},
+		{
+			.id = 0x300,
+			.num = { 10, 18, 18, 18, 18 },
+			.src_descr = "Mix %c",
+			.src_num_offset = 65,
+			.dst_descr = "Mixer Input %02d Capture"
+		},
+		{
+			.id = 0x600,
+			.num = { 6, 6, 6, 6, 6 },
+			.src_descr = "PCM %d",
+			.src_num_offset = 1,
+			.dst_descr = "PCM %02d Capture"
+		},
+	},
+};
+
+static const struct scarlett2_device_info s18i8_gen2_info = {
+	/* The first two analogue inputs can be switched between line
+	 * and instrument levels.
+	 */
+	.level_input_count = 2,
+
+	/* The first four analogue inputs have an optional pad. */
+	.pad_input_count = 4,
+
+	.line_out_descrs = {
+		"Monitor L",
+		"Monitor R",
+		"Headphones 1 L",
+		"Headphones 1 R",
+		"Headphones 2 L",
+		"Headphones 2 R",
+	},
+
+	.ports = {
+		{
+			.id = 0x000,
+			.num = { 1, 0, 8, 8, 4 },
+			.src_descr = "Off",
+			.src_num_offset = 0,
+		},
+		{
+			.id = 0x080,
+			.num = { 8, 6, 6, 6, 6 },
+			.src_descr = "Analogue %d",
+			.src_num_offset = 1,
+			.dst_descr = "Analogue Output %02d Playback"
+		},
+		{
+			/* S/PDIF outputs aren't available at 192KHz
+			 * but are included in the USB mux I/O
+			 * assignment message anyway
+			 */
+			.id = 0x180,
+			.num = { 2, 2, 2, 2, 2 },
+			.src_descr = "S/PDIF %d",
+			.src_num_offset = 1,
+			.dst_descr = "S/PDIF Output %d Playback"
+		},
+		{
+			.id = 0x200,
+			.num = { 8, 0, 0, 0, 0 },
+			.src_descr = "ADAT %d",
+			.src_num_offset = 1,
+		},
+		{
+			.id = 0x300,
+			.num = { 10, 18, 18, 18, 18 },
+			.src_descr = "Mix %c",
+			.src_num_offset = 65,
+			.dst_descr = "Mixer Input %02d Capture"
+		},
+		{
+			.id = 0x600,
+			.num = { 20, 18, 18, 14, 10 },
+			.src_descr = "PCM %d",
+			.src_num_offset = 1,
+			.dst_descr = "PCM %02d Capture"
+		},
+	},
+};
+
+static const struct scarlett2_device_info s18i20_gen2_info = {
+	/* The analogue line outputs on the 18i20 can be switched
+	 * between software and hardware volume control
+	 */
+	.line_out_hw_vol = 1,
+
+	/* Mute and dim buttons */
+	.button_count = 2,
+
+	.line_out_descrs = {
+		"Monitor L",
+		"Monitor R",
+		NULL,
+		NULL,
+		NULL,
+		NULL,
+		"Headphones 1 L",
+		"Headphones 1 R",
+		"Headphones 2 L",
+		"Headphones 2 R",
+	},
+
+	.ports = {
+		{
+			.id = 0x000,
+			.num = { 1, 0, 8, 8, 6 },
+			.src_descr = "Off",
+			.src_num_offset = 0,
+		},
+		{
+			.id = 0x080,
+			.num = { 8, 10, 10, 10, 10 },
+			.src_descr = "Analogue %d",
+			.src_num_offset = 1,
+			.dst_descr = "Analogue Output %02d Playback"
+		},
+		{
+			/* S/PDIF outputs aren't available at 192KHz
+			 * but are included in the USB mux I/O
+			 * assignment message anyway
+			 */
+			.id = 0x180,
+			.num = { 2, 2, 2, 2, 2 },
+			.src_descr = "S/PDIF %d",
+			.src_num_offset = 1,
+			.dst_descr = "S/PDIF Output %d Playback"
+		},
+		{
+			.id = 0x200,
+			.num = { 8, 8, 8, 4, 0 },
+			.src_descr = "ADAT %d",
+			.src_num_offset = 1,
+			.dst_descr = "ADAT Output %d Playback"
+		},
+		{
+			.id = 0x300,
+			.num = { 10, 18, 18, 18, 18 },
+			.src_descr = "Mix %c",
+			.src_num_offset = 65,
+			.dst_descr = "Mixer Input %02d Capture"
+		},
+		{
+			.id = 0x600,
+			.num = { 20, 18, 18, 14, 10 },
+			.src_descr = "PCM %d",
+			.src_num_offset = 1,
+			.dst_descr = "PCM %02d Capture"
+		},
+	},
+};
+
+/* get the starting port index number for a given port type/direction */
+static int scarlett2_get_port_start_num(const struct scarlett2_ports *ports,
+					int direction, int port_type)
+{
+	int i, num = 0;
+
+	for (i = 0; i < port_type; i++)
+		num += ports[i].num[direction];
+
+	return num;
+}
+
+/*** USB Interactions ***/
+
+/* Vendor-Specific Interface, Endpoint, MaxPacketSize, Interval */
+#define SCARLETT2_USB_VENDOR_SPECIFIC_INTERFACE 5
+#define SCARLETT2_USB_INTERRUPT_ENDPOINT 4
+#define SCARLETT2_USB_INTERRUPT_MAX_DATA 64
+#define SCARLETT2_USB_INTERRUPT_INTERVAL 3
+
+/* Interrupt flags for volume and mute/dim button changes */
+#define SCARLETT2_USB_INTERRUPT_VOL_CHANGE 0x400000
+#define SCARLETT2_USB_INTERRUPT_BUTTON_CHANGE 0x200000
+
+/* Commands for sending/receiving requests/responses */
+#define SCARLETT2_USB_VENDOR_SPECIFIC_CMD_REQ 2
+#define SCARLETT2_USB_VENDOR_SPECIFIC_CMD_RESP 3
+
+#define SCARLETT2_USB_INIT_SEQ 0x00000000
+#define SCARLETT2_USB_GET_METER_LEVELS 0x00001001
+#define SCARLETT2_USB_SET_MIX 0x00002002
+#define SCARLETT2_USB_SET_MUX 0x00003002
+#define SCARLETT2_USB_GET_DATA 0x00800000
+#define SCARLETT2_USB_SET_DATA 0x00800001
+#define SCARLETT2_USB_DATA_CMD 0x00800002
+#define SCARLETT2_USB_CONFIG_SAVE 6
+
+#define SCARLETT2_USB_VOLUME_STATUS_OFFSET 0x31
+#define SCARLETT2_USB_METER_LEVELS_GET_MAGIC 1
+
+/* volume status is read together (matches scarlett2_config_items[]) */
+struct scarlett2_usb_volume_status {
+	/* mute & dim buttons */
+	u8 buttons[SCARLETT2_BUTTON_MAX];
+
+	u8 pad1;
+
+	/* software volume setting */
+	s16 sw_vol[SCARLETT2_ANALOGUE_MAX];
+
+	/* actual volume of output inc. dim (-18dB) */
+	s16 hw_vol[SCARLETT2_ANALOGUE_MAX];
+
+	u8 pad2[SCARLETT2_ANALOGUE_MAX];
+
+	/* sw (0) or hw (1) controlled */
+	u8 sw_hw_switch[SCARLETT2_ANALOGUE_MAX];
+
+	u8 pad3[6];
+
+	/* front panel volume knob */
+	s16 master_vol;
+} __packed;
+
+/* Configuration parameters that can be read and written */
+enum {
+	SCARLETT2_CONFIG_BUTTONS = 0,
+	SCARLETT2_CONFIG_LINE_OUT_VOLUME = 1,
+	SCARLETT2_CONFIG_SW_HW_SWITCH = 2,
+	SCARLETT2_CONFIG_LEVEL_SWITCH = 3,
+	SCARLETT2_CONFIG_PAD_SWITCH = 4,
+	SCARLETT2_CONFIG_COUNT = 5
+};
+
+/* Location, size, and activation command number for the configuration
+ * parameters
+ */
+struct scarlett2_config {
+	u8 offset;
+	u8 size;
+	u8 activate;
+};
+
+static const struct scarlett2_config
+		scarlett2_config_items[SCARLETT2_CONFIG_COUNT] = {
+	/* Mute/Dim Buttons */
+	{
+		.offset = 0x31,
+		.size = 1,
+		.activate = 2
+	},
+
+	/* Line Out Volume */
+	{
+		.offset = 0x34,
+		.size = 2,
+		.activate = 1
+	},
+
+	/* SW/HW Volume Switch */
+	{
+		.offset = 0x66,
+		.size = 1,
+		.activate = 3
+	},
+
+	/* Level Switch */
+	{
+		.offset = 0x7c,
+		.size = 1,
+		.activate = 7
+	},
+
+	/* Pad Switch */
+	{
+		.offset = 0x84,
+		.size = 1,
+		.activate = 8
+	}
+};
+
+/* proprietary request/response format */
+struct scarlett2_usb_packet {
+	u32 cmd;
+	u16 size;
+	u16 seq;
+	u32 error;
+	u32 pad;
+	u8 data[];
+};
+
+#define SCARLETT2_USB_PACKET_LEN (sizeof(struct scarlett2_usb_packet))
+
+static void scarlett2_fill_request_header(struct scarlett2_mixer_data *private,
+					  struct scarlett2_usb_packet *req,
+					  u32 cmd, u16 req_size)
+{
+	/* sequence must go up by 1 for each request */
+	u16 seq = private->scarlett2_seq++;
+
+	req->cmd = cpu_to_le32(cmd);
+	req->size = cpu_to_le16(req_size);
+	req->seq = cpu_to_le16(seq);
+	req->error = 0;
+	req->pad = 0;
+}
+
+/* Send a proprietary format request to the Scarlett interface */
+static int scarlett2_usb(
+	struct usb_mixer_interface *mixer, u32 cmd,
+	void *req_data, u16 req_size, void *resp_data, u16 resp_size)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	u16 req_buf_size = sizeof(struct scarlett2_usb_packet) + req_size;
+	u16 resp_buf_size = sizeof(struct scarlett2_usb_packet) + resp_size;
+
+	struct scarlett2_usb_packet *req = 0, *resp = 0;
+
+	int err = 0;
+
+	mutex_lock(&private->usb_mutex);
+
+	/* build request message and send it */
+
+	req = kmalloc(req_buf_size, GFP_KERNEL);
+	if (!req) {
+		err = -ENOMEM;
+		goto unlock;
+	}
+
+	scarlett2_fill_request_header(private, req, cmd, req_size);
+
+	if (req_size)
+		memcpy(req->data, req_data, req_size);
+
+	err = snd_usb_ctl_msg(mixer->chip->dev,
+			usb_sndctrlpipe(mixer->chip->dev, 0),
+			SCARLETT2_USB_VENDOR_SPECIFIC_CMD_REQ,
+			USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_OUT,
+			0,
+			SCARLETT2_USB_VENDOR_SPECIFIC_INTERFACE,
+			req,
+			req_buf_size);
+
+	if (err != req_buf_size) {
+		usb_audio_err(
+			mixer->chip,
+			"Scarlett Gen 2 USB request result cmd %x was %d\n",
+			cmd, err);
+		err = -EINVAL;
+		goto unlock;
+	}
+
+	/* send a second message to get the response */
+
+	resp = kmalloc(resp_buf_size, GFP_KERNEL);
+	if (!resp) {
+		err = -ENOMEM;
+		goto unlock;
+	}
+
+	err = snd_usb_ctl_msg(mixer->chip->dev,
+			usb_sndctrlpipe(mixer->chip->dev, 0),
+			SCARLETT2_USB_VENDOR_SPECIFIC_CMD_RESP,
+			USB_RECIP_INTERFACE | USB_TYPE_CLASS | USB_DIR_IN,
+			0,
+			SCARLETT2_USB_VENDOR_SPECIFIC_INTERFACE,
+			resp,
+			resp_buf_size);
+
+	/* validate the response */
+
+	if (err != resp_buf_size) {
+		usb_audio_err(
+			mixer->chip,
+			"Scarlett Gen 2 USB response result cmd %x was %d\n",
+			cmd, err);
+		err = -EINVAL;
+		goto unlock;
+	}
+
+	if (resp->cmd != req->cmd ||
+	    resp->seq != req->seq ||
+	    resp_size != le16_to_cpu(resp->size) ||
+	    resp->error ||
+	    resp->pad) {
+		usb_audio_err(
+			mixer->chip,
+			"Scarlett Gen 2 USB invalid response; "
+			   "cmd tx/rx %d/%d seq %d/%d size %d/%d "
+			   "error %d pad %d\n",
+			le16_to_cpu(req->cmd), le16_to_cpu(resp->cmd),
+			le16_to_cpu(req->seq), le16_to_cpu(resp->seq),
+			resp_size, le16_to_cpu(resp->size),
+			le16_to_cpu(resp->error),
+			le16_to_cpu(resp->pad));
+		err = -EINVAL;
+		goto unlock;
+	}
+
+	if (resp_size > 0)
+		memcpy(resp_data, resp->data, resp_size);
+
+unlock:
+	kfree(req);
+	kfree(resp);
+	mutex_unlock(&private->usb_mutex);
+	return err;
+}
+
+/* Send SCARLETT2_USB_DATA_CMD SCARLETT2_USB_CONFIG_SAVE */
+static void scarlett2_config_save(struct work_struct *work)
+{
+	struct scarlett2_mixer_data *private =
+		container_of(work, struct scarlett2_mixer_data, work.work);
+	struct usb_mixer_interface *mixer = private->mixer;
+	u32 req = cpu_to_le32(SCARLETT2_USB_CONFIG_SAVE);
+
+	scarlett2_usb(mixer, SCARLETT2_USB_DATA_CMD,
+		      &req, sizeof(u32),
+		      NULL, 0);
+}
+
+/* Send a USB message to set a configuration parameter (volume level,
+ * sw/hw volume switch, line/inst level switch, or pad switch)
+ */
+static int scarlett2_usb_set_config(
+	struct usb_mixer_interface *mixer,
+	int config_item_num, int index, int value)
+{
+	const struct scarlett2_config config_item =
+	       scarlett2_config_items[config_item_num];
+	struct {
+		u32 offset;
+		u32 bytes;
+		s32 value;
+	} __packed req;
+	u32 req2;
+	int err;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	/* Send the configuration parameter data */
+	req.offset = cpu_to_le32(config_item.offset + index * config_item.size);
+	req.bytes = cpu_to_le32(config_item.size);
+	req.value = cpu_to_le32(value);
+	err = scarlett2_usb(mixer, SCARLETT2_USB_SET_DATA,
+			    &req, sizeof(u32) * 2 + config_item.size,
+			    NULL, 0);
+	if (err < 0)
+		return err;
+
+	/* Activate the change */
+	req2 = cpu_to_le32(config_item.activate);
+	err = scarlett2_usb(mixer, SCARLETT2_USB_DATA_CMD,
+			    &req2, sizeof(req2), NULL, 0);
+	if (err < 0)
+		return err;
+
+	/* Schedule the change to be written to NVRAM */
+	schedule_delayed_work(&private->work, msecs_to_jiffies(2000));
+
+	return 0;
+}
+
+/* Send a USB message to get data; result placed in *buf */
+static int scarlett2_usb_get(
+	struct usb_mixer_interface *mixer,
+	int offset, void *buf, int size)
+{
+	struct {
+		u32 offset;
+		u32 size;
+	} __packed req;
+
+	req.offset = cpu_to_le32(offset);
+	req.size = cpu_to_le32(size);
+	return scarlett2_usb(mixer, SCARLETT2_USB_GET_DATA,
+			     &req, sizeof(req), buf, size);
+}
+
+/* Send a USB message to get configuration parameters; result placed in *buf */
+static int scarlett2_usb_get_config(
+	struct usb_mixer_interface *mixer,
+	int config_item_num, int count, void *buf)
+{
+	const struct scarlett2_config config_item =
+	       scarlett2_config_items[config_item_num];
+	int size = config_item.size * count;
+
+	return scarlett2_usb_get(mixer, config_item.offset, buf, size);
+}
+
+/* Send a USB message to get volume status; result placed in *buf */
+static int scarlett2_usb_get_volume_status(
+	struct usb_mixer_interface *mixer,
+	struct scarlett2_usb_volume_status *buf)
+{
+	return scarlett2_usb_get(mixer, SCARLETT2_USB_VOLUME_STATUS_OFFSET,
+				 buf, sizeof(*buf));
+}
+
+/* Send a USB message to set the volumes for all inputs of one mix
+ * (values obtained from private->mix[])
+ */
+static int scarlett2_usb_set_mix(struct usb_mixer_interface *mixer,
+				     int mix_num)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_device_info *info = private->info;
+
+	struct {
+		u16 mix_num;
+		u16 data[SCARLETT2_INPUT_MIX_MAX];
+	} __packed req;
+
+	int i, j;
+	int num_mixer_in =
+		info->ports[SCARLETT2_PORT_TYPE_MIX].num[SCARLETT2_PORT_OUT];
+
+	req.mix_num = cpu_to_le16(mix_num);
+
+	for (i = 0, j = mix_num * num_mixer_in; i < num_mixer_in; i++, j++)
+		req.data[i] = cpu_to_le16(
+			scarlett2_mixer_values[private->mix[j]]
+		);
+
+	return scarlett2_usb(mixer, SCARLETT2_USB_SET_MIX,
+			     &req, (num_mixer_in + 1) * sizeof(u16),
+			     NULL, 0);
+}
+
+/* Convert a port number index (per info->ports) to a hardware ID */
+static u32 scarlett2_mux_src_num_to_id(const struct scarlett2_ports *ports,
+				       int num)
+{
+	int port_type;
+
+	for (port_type = 0;
+	     port_type < SCARLETT2_PORT_TYPE_COUNT;
+	     port_type++) {
+		if (num < ports[port_type].num[SCARLETT2_PORT_IN])
+			return ports[port_type].id | num;
+		num -= ports[port_type].num[SCARLETT2_PORT_IN];
+	}
+
+	/* Oops */
+	return 0;
+}
+
+/* Send USB messages to set mux inputs */
+static int scarlett2_usb_set_mux(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_device_info *info = private->info;
+	const struct scarlett2_ports *ports = info->ports;
+	int rate, port_dir_rate;
+
+	static const int assignment_order[SCARLETT2_PORT_TYPE_COUNT] = {
+		SCARLETT2_PORT_TYPE_PCM,
+		SCARLETT2_PORT_TYPE_ANALOGUE,
+		SCARLETT2_PORT_TYPE_SPDIF,
+		SCARLETT2_PORT_TYPE_ADAT,
+		SCARLETT2_PORT_TYPE_MIX,
+		SCARLETT2_PORT_TYPE_NONE,
+	};
+
+	struct {
+		u16 pad;
+		u16 num;
+		u32 data[SCARLETT2_MUX_MAX];
+	} __packed req;
+
+	req.pad = 0;
+
+	/* mux settings for each rate */
+	for (rate = 0, port_dir_rate = SCARLETT2_PORT_OUT_44;
+	     port_dir_rate <= SCARLETT2_PORT_OUT_176;
+	     rate++, port_dir_rate++) {
+		int order_num, i, err;
+
+		req.num = cpu_to_le16(rate);
+
+		for (order_num = 0, i = 0;
+		     order_num < SCARLETT2_PORT_TYPE_COUNT;
+		     order_num++) {
+			int port_type = assignment_order[order_num];
+			int j = scarlett2_get_port_start_num(ports,
+							     SCARLETT2_PORT_OUT,
+							     port_type);
+			int port_id = ports[port_type].id;
+			int channel;
+
+			for (channel = 0;
+			     channel < ports[port_type].num[port_dir_rate];
+			     channel++, i++, j++)
+				/* lower 12 bits for the destination and
+				 * next 12 bits for the source
+				 */
+				req.data[i] = !port_id
+					? 0
+					: cpu_to_le32(
+						port_id |
+						channel |
+						scarlett2_mux_src_num_to_id(
+							ports, private->mux[j]
+						) << 12
+					  );
+
+			/* skip private->mux[j] entries not output */
+			j += ports[port_type].num[SCARLETT2_PORT_OUT] -
+			     ports[port_type].num[port_dir_rate];
+		}
+
+		err = scarlett2_usb(mixer, SCARLETT2_USB_SET_MUX,
+				    &req, (i + 1) * sizeof(u32),
+				    NULL, 0);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+
+/* Send USB message to get meter levels */
+static int scarlett2_usb_get_meter_levels(struct usb_mixer_interface *mixer,
+					  u16 *levels)
+{
+	struct {
+		u16 pad;
+		u16 num_meters;
+		u32 magic;
+	} __packed req;
+	u32 resp[SCARLETT2_NUM_METERS];
+	int i, err;
+
+	req.pad = 0;
+	req.num_meters = cpu_to_le16(SCARLETT2_NUM_METERS);
+	req.magic = cpu_to_le32(SCARLETT2_USB_METER_LEVELS_GET_MAGIC);
+	err = scarlett2_usb(mixer, SCARLETT2_USB_GET_METER_LEVELS,
+			    &req, sizeof(req), resp, sizeof(resp));
+	if (err < 0)
+		return err;
+
+	/* copy, convert to u16 */
+	for (i = 0; i < SCARLETT2_NUM_METERS; i++)
+		levels[i] = resp[i];
+
+	return 0;
+}
+
+/*** Control Functions ***/
+
+/* helper function to create a new control */
+static int scarlett2_add_new_ctl(struct usb_mixer_interface *mixer,
+				 const struct snd_kcontrol_new *ncontrol,
+				 int index, int channels, const char *name,
+				 struct snd_kcontrol **kctl_return)
+{
+	struct snd_kcontrol *kctl;
+	struct usb_mixer_elem_info *elem;
+	int err;
+
+	elem = kzalloc(sizeof(*elem), GFP_KERNEL);
+	if (!elem)
+		return -ENOMEM;
+
+	elem->head.mixer = mixer;
+	elem->control = index;
+	elem->head.id = index;
+	elem->channels = channels;
+
+	kctl = snd_ctl_new1(ncontrol, elem);
+	if (!kctl) {
+		kfree(elem);
+		return -ENOMEM;
+	}
+	kctl->private_free = snd_usb_mixer_elem_free;
+
+	strlcpy(kctl->id.name, name, sizeof(kctl->id.name));
+
+	err = snd_usb_mixer_add_control(&elem->head, kctl);
+	if (err < 0)
+		return err;
+
+	if (kctl_return)
+		*kctl_return = kctl;
+
+	return 0;
+}
+
+/*** Analogue Line Out Volume Controls ***/
+
+/* Update hardware volume controls after receiving notification that
+ * they have changed
+ */
+static int scarlett2_update_volumes(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_ports *ports = private->info->ports;
+	struct scarlett2_usb_volume_status volume_status;
+	int num_line_out =
+		ports[SCARLETT2_PORT_TYPE_ANALOGUE].num[SCARLETT2_PORT_OUT];
+	int err, i;
+
+	private->vol_updated = 0;
+
+	err = scarlett2_usb_get_volume_status(mixer, &volume_status);
+	if (err < 0)
+		return err;
+
+	private->master_vol = clamp(
+		volume_status.master_vol + SCARLETT_VOLUME_BIAS,
+		0, SCARLETT_VOLUME_BIAS);
+
+	for (i = 0; i < num_line_out; i++) {
+		if (private->vol_sw_hw_switch[i])
+			private->vol[i] = private->master_vol;
+	}
+
+	for (i = 0; i < private->info->button_count; i++)
+		private->buttons[i] = !!volume_status.buttons[i];
+
+	return 0;
+}
+
+static int scarlett2_volume_ctl_info(struct snd_kcontrol *kctl,
+				     struct snd_ctl_elem_info *uinfo)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = elem->channels;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = SCARLETT_VOLUME_BIAS;
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int scarlett2_master_volume_ctl_get(struct snd_kcontrol *kctl,
+					   struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	if (private->vol_updated) {
+		mutex_lock(&private->data_mutex);
+		scarlett2_update_volumes(mixer);
+		mutex_unlock(&private->data_mutex);
+	}
+
+	ucontrol->value.integer.value[0] = private->master_vol;
+	return 0;
+}
+
+static int scarlett2_volume_ctl_get(struct snd_kcontrol *kctl,
+				    struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	int index = elem->control;
+
+	if (private->vol_updated) {
+		mutex_lock(&private->data_mutex);
+		scarlett2_update_volumes(mixer);
+		mutex_unlock(&private->data_mutex);
+	}
+
+	ucontrol->value.integer.value[0] = private->vol[index];
+	return 0;
+}
+
+static int scarlett2_volume_ctl_put(struct snd_kcontrol *kctl,
+				    struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	int index = elem->control;
+	int oval, val, err = 0;
+
+	cancel_delayed_work_sync(&private->work);
+	mutex_lock(&private->data_mutex);
+
+	oval = private->vol[index];
+	val = ucontrol->value.integer.value[0];
+
+	if (oval == val)
+		goto unlock;
+
+	private->vol[index] = val;
+	err = scarlett2_usb_set_config(mixer, SCARLETT2_CONFIG_LINE_OUT_VOLUME,
+				       index, val - SCARLETT_VOLUME_BIAS);
+	if (err == 0)
+		err = 1;
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const DECLARE_TLV_DB_MINMAX(
+	db_scale_scarlett_gain, -SCARLETT_VOLUME_BIAS * 100, 0
+);
+
+static const struct snd_kcontrol_new scarlett2_master_volume_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.access = SNDRV_CTL_ELEM_ACCESS_READ |
+		  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+	.name = "",
+	.info = scarlett2_volume_ctl_info,
+	.get  = scarlett2_master_volume_ctl_get,
+	.private_value = 0, /* max value */
+	.tlv = { .p = db_scale_scarlett_gain }
+};
+
+static const struct snd_kcontrol_new scarlett2_line_out_volume_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+		  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+	.name = "",
+	.info = scarlett2_volume_ctl_info,
+	.get  = scarlett2_volume_ctl_get,
+	.put  = scarlett2_volume_ctl_put,
+	.private_value = 0, /* max value */
+	.tlv = { .p = db_scale_scarlett_gain }
+};
+
+/*** HW/SW Volume Switch Controls ***/
+
+static int scarlett2_sw_hw_enum_ctl_info(struct snd_kcontrol *kctl,
+					 struct snd_ctl_elem_info *uinfo)
+{
+	static const char *const values[2] = {
+		"SW", "HW"
+	};
+
+	return snd_ctl_enum_info(uinfo, 1, 2, values);
+}
+
+static int scarlett2_sw_hw_enum_ctl_get(struct snd_kcontrol *kctl,
+					struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett2_mixer_data *private = elem->head.mixer->private_data;
+
+	ucontrol->value.enumerated.item[0] =
+		private->vol_sw_hw_switch[elem->control];
+	return 0;
+}
+
+static int scarlett2_sw_hw_enum_ctl_put(struct snd_kcontrol *kctl,
+					struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	int index = elem->control;
+	int oval, val, err = 0;
+
+	cancel_delayed_work_sync(&private->work);
+	mutex_lock(&private->data_mutex);
+
+	oval = private->vol_sw_hw_switch[index];
+	val = !!ucontrol->value.integer.value[0];
+
+	if (oval == val)
+		goto unlock;
+
+	private->vol_sw_hw_switch[index] = val;
+
+	/* Change access mode to RO (hardware controlled volume)
+	 * or RW (software controlled volume)
+	 */
+	if (val)
+		private->vol_ctls[index]->vd[0].access &=
+			~SNDRV_CTL_ELEM_ACCESS_WRITE;
+	else
+		private->vol_ctls[index]->vd[0].access |=
+			SNDRV_CTL_ELEM_ACCESS_WRITE;
+
+	/* Reset volume to master volume */
+	private->vol[index] = private->master_vol;
+
+	/* Set SW volume to current HW volume */
+	err = scarlett2_usb_set_config(
+		mixer, SCARLETT2_CONFIG_LINE_OUT_VOLUME,
+		index, private->master_vol - SCARLETT_VOLUME_BIAS);
+	if (err < 0)
+		goto unlock;
+
+	/* Notify of RO/RW change */
+	snd_ctl_notify(mixer->chip->card, SNDRV_CTL_EVENT_MASK_INFO,
+		       &private->vol_ctls[index]->id);
+
+	/* Send SW/HW switch change to the device */
+	err = scarlett2_usb_set_config(mixer, SCARLETT2_CONFIG_SW_HW_SWITCH,
+				       index, val);
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const struct snd_kcontrol_new scarlett2_sw_hw_enum_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.name = "",
+	.info = scarlett2_sw_hw_enum_ctl_info,
+	.get  = scarlett2_sw_hw_enum_ctl_get,
+	.put  = scarlett2_sw_hw_enum_ctl_put,
+};
+
+/*** Line Level/Instrument Level Switch Controls ***/
+
+static int scarlett2_level_enum_ctl_info(struct snd_kcontrol *kctl,
+					 struct snd_ctl_elem_info *uinfo)
+{
+	static const char *const values[2] = {
+		"Line", "Inst"
+	};
+
+	return snd_ctl_enum_info(uinfo, 1, 2, values);
+}
+
+static int scarlett2_level_enum_ctl_get(struct snd_kcontrol *kctl,
+					struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett2_mixer_data *private = elem->head.mixer->private_data;
+
+	ucontrol->value.enumerated.item[0] =
+		private->level_switch[elem->control];
+	return 0;
+}
+
+static int scarlett2_level_enum_ctl_put(struct snd_kcontrol *kctl,
+					struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	int index = elem->control;
+	int oval, val, err = 0;
+
+	cancel_delayed_work_sync(&private->work);
+	mutex_lock(&private->data_mutex);
+
+	oval = private->level_switch[index];
+	val = !!ucontrol->value.integer.value[0];
+
+	if (oval == val)
+		goto unlock;
+
+	private->level_switch[index] = val;
+
+	/* Send switch change to the device */
+	err = scarlett2_usb_set_config(mixer, SCARLETT2_CONFIG_LEVEL_SWITCH,
+				       index, val);
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const struct snd_kcontrol_new scarlett2_level_enum_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.name = "",
+	.info = scarlett2_level_enum_ctl_info,
+	.get  = scarlett2_level_enum_ctl_get,
+	.put  = scarlett2_level_enum_ctl_put,
+};
+
+/*** Pad Switch Controls ***/
+
+static int scarlett2_pad_ctl_get(struct snd_kcontrol *kctl,
+				 struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett2_mixer_data *private = elem->head.mixer->private_data;
+
+	ucontrol->value.enumerated.item[0] =
+		private->pad_switch[elem->control];
+	return 0;
+}
+
+static int scarlett2_pad_ctl_put(struct snd_kcontrol *kctl,
+				 struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	int index = elem->control;
+	int oval, val, err = 0;
+
+	cancel_delayed_work_sync(&private->work);
+	mutex_lock(&private->data_mutex);
+
+	oval = private->pad_switch[index];
+	val = !!ucontrol->value.integer.value[0];
+
+	if (oval == val)
+		goto unlock;
+
+	private->pad_switch[index] = val;
+
+	/* Send switch change to the device */
+	err = scarlett2_usb_set_config(mixer, SCARLETT2_CONFIG_PAD_SWITCH,
+				       index, val);
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const struct snd_kcontrol_new scarlett2_pad_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.name = "",
+	.info = snd_ctl_boolean_mono_info,
+	.get  = scarlett2_pad_ctl_get,
+	.put  = scarlett2_pad_ctl_put,
+};
+
+/*** Mute/Dim Controls ***/
+
+static int scarlett2_button_ctl_get(struct snd_kcontrol *kctl,
+				    struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	if (private->vol_updated) {
+		mutex_lock(&private->data_mutex);
+		scarlett2_update_volumes(mixer);
+		mutex_unlock(&private->data_mutex);
+	}
+
+	ucontrol->value.enumerated.item[0] = private->buttons[elem->control];
+	return 0;
+}
+
+static int scarlett2_button_ctl_put(struct snd_kcontrol *kctl,
+				    struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	int index = elem->control;
+	int oval, val, err = 0;
+
+	cancel_delayed_work_sync(&private->work);
+	mutex_lock(&private->data_mutex);
+
+	oval = private->buttons[index];
+	val = !!ucontrol->value.integer.value[0];
+
+	if (oval == val)
+		goto unlock;
+
+	private->buttons[index] = val;
+
+	/* Send switch change to the device */
+	err = scarlett2_usb_set_config(mixer, SCARLETT2_CONFIG_BUTTONS,
+				       index, val);
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const struct snd_kcontrol_new scarlett2_button_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.name = "",
+	.info = snd_ctl_boolean_mono_info,
+	.get  = scarlett2_button_ctl_get,
+	.put  = scarlett2_button_ctl_put
+};
+
+/*** Create the analogue output controls ***/
+
+static int scarlett2_add_line_out_ctls(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_device_info *info = private->info;
+	const struct scarlett2_ports *ports = info->ports;
+	int num_line_out =
+		ports[SCARLETT2_PORT_TYPE_ANALOGUE].num[SCARLETT2_PORT_OUT];
+	int err, i;
+	char s[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+
+	/* Add R/O HW volume control */
+	if (info->line_out_hw_vol) {
+		snprintf(s, sizeof(s), "Master HW Playback Volume");
+		err = scarlett2_add_new_ctl(mixer,
+					    &scarlett2_master_volume_ctl,
+					    0, 1, s, &private->master_vol_ctl);
+		if (err < 0)
+			return err;
+	}
+
+	/* Add volume controls */
+	for (i = 0; i < num_line_out; i++) {
+
+		/* Fader */
+		if (info->line_out_descrs[i])
+			snprintf(s, sizeof(s),
+				 "Line %02d (%s) Playback Volume",
+				 i + 1, info->line_out_descrs[i]);
+		else
+			snprintf(s, sizeof(s),
+				 "Line %02d Playback Volume",
+				 i + 1);
+		err = scarlett2_add_new_ctl(mixer,
+					    &scarlett2_line_out_volume_ctl,
+					    i, 1, s, &private->vol_ctls[i]);
+		if (err < 0)
+			return err;
+
+		/* Make the fader read-only if the SW/HW switch is set to HW */
+		if (private->vol_sw_hw_switch[i])
+			private->vol_ctls[i]->vd[0].access &=
+				~SNDRV_CTL_ELEM_ACCESS_WRITE;
+
+		/* SW/HW Switch */
+		if (info->line_out_hw_vol) {
+			snprintf(s, sizeof(s),
+				 "Line Out %02d Volume Control Playback Enum",
+				 i + 1);
+			err = scarlett2_add_new_ctl(mixer,
+						    &scarlett2_sw_hw_enum_ctl,
+						    i, 1, s, NULL);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	/* Add HW button controls */
+	for (i = 0; i < private->info->button_count; i++) {
+		err = scarlett2_add_new_ctl(mixer, &scarlett2_button_ctl,
+					    i, 1, scarlett2_button_names[i],
+					    &private->button_ctls[i]);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+
+/*** Create the analogue input controls ***/
+
+static int scarlett2_add_line_in_ctls(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_device_info *info = private->info;
+	int err, i;
+	char s[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+
+	/* Add input level (line/inst) controls */
+	for (i = 0; i < info->level_input_count; i++) {
+		snprintf(s, sizeof(s), "Line In %d Level Capture Enum", i + 1);
+		err = scarlett2_add_new_ctl(mixer, &scarlett2_level_enum_ctl,
+					    i, 1, s, NULL);
+		if (err < 0)
+			return err;
+	}
+
+	/* Add input pad controls */
+	for (i = 0; i < info->pad_input_count; i++) {
+		snprintf(s, sizeof(s), "Line In %d Pad Capture Switch", i + 1);
+		err = scarlett2_add_new_ctl(mixer, &scarlett2_pad_ctl,
+					    i, 1, s, NULL);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+
+/*** Mixer Volume Controls ***/
+
+static int scarlett2_mixer_ctl_info(struct snd_kcontrol *kctl,
+				    struct snd_ctl_elem_info *uinfo)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = elem->channels;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = SCARLETT_MIXER_MAX_VALUE;
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int scarlett2_mixer_ctl_get(struct snd_kcontrol *kctl,
+				   struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett2_mixer_data *private = elem->head.mixer->private_data;
+
+	ucontrol->value.integer.value[0] = private->mix[elem->control];
+	return 0;
+}
+
+static int scarlett2_mixer_ctl_put(struct snd_kcontrol *kctl,
+				   struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_device_info *info = private->info;
+	const struct scarlett2_ports *ports = info->ports;
+	int oval, val, num_mixer_in, mix_num, err = 0;
+
+	mutex_lock(&private->data_mutex);
+
+	oval = private->mix[elem->control];
+	val = ucontrol->value.integer.value[0];
+	num_mixer_in = ports[SCARLETT2_PORT_TYPE_MIX].num[SCARLETT2_PORT_OUT];
+	mix_num = elem->control / num_mixer_in;
+
+	if (oval == val)
+		goto unlock;
+
+	private->mix[elem->control] = val;
+	err = scarlett2_usb_set_mix(mixer, mix_num);
+	if (err == 0)
+		err = 1;
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const DECLARE_TLV_DB_MINMAX(
+	db_scale_scarlett_mixer,
+	SCARLETT_MIXER_MIN_DB * 100,
+	SCARLETT_MIXER_MAX_DB * 100
+);
+
+static const struct snd_kcontrol_new scarlett2_mixer_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+		  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+	.name = "",
+	.info = scarlett2_mixer_ctl_info,
+	.get  = scarlett2_mixer_ctl_get,
+	.put  = scarlett2_mixer_ctl_put,
+	.private_value = SCARLETT_MIXER_MAX_DB, /* max value */
+	.tlv = { .p = db_scale_scarlett_mixer }
+};
+
+static int scarlett2_add_mixer_ctls(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_ports *ports = private->info->ports;
+	int err, i, j;
+	int index;
+	char s[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+
+	int num_inputs = ports[SCARLETT2_PORT_TYPE_MIX].num[SCARLETT2_PORT_OUT];
+	int num_outputs = ports[SCARLETT2_PORT_TYPE_MIX].num[SCARLETT2_PORT_IN];
+
+	for (i = 0, index = 0; i < num_outputs; i++) {
+		for (j = 0; j < num_inputs; j++, index++) {
+			snprintf(s, sizeof(s),
+				 "Mix %c Input %02d Playback Volume",
+				 'A' + i, j + 1);
+			err = scarlett2_add_new_ctl(mixer, &scarlett2_mixer_ctl,
+						    index, 1, s, NULL);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	return 0;
+}
+
+/*** Mux Source Selection Controls ***/
+
+static int scarlett2_mux_src_enum_ctl_info(struct snd_kcontrol *kctl,
+					   struct snd_ctl_elem_info *uinfo)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett2_mixer_data *private = elem->head.mixer->private_data;
+	const struct scarlett2_ports *ports = private->info->ports;
+	unsigned int item = uinfo->value.enumerated.item;
+	int items = private->num_mux_srcs;
+	int port_type;
+
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_ENUMERATED;
+	uinfo->count = elem->channels;
+	uinfo->value.enumerated.items = items;
+
+	if (item >= items)
+		item = uinfo->value.enumerated.item = items - 1;
+
+	for (port_type = 0;
+	     port_type < SCARLETT2_PORT_TYPE_COUNT;
+	     port_type++) {
+		if (item < ports[port_type].num[SCARLETT2_PORT_IN]) {
+			sprintf(uinfo->value.enumerated.name,
+				ports[port_type].src_descr,
+				item + ports[port_type].src_num_offset);
+			return 0;
+		}
+		item -= ports[port_type].num[SCARLETT2_PORT_IN];
+	}
+
+	return -EINVAL;
+}
+
+static int scarlett2_mux_src_enum_ctl_get(struct snd_kcontrol *kctl,
+					  struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett2_mixer_data *private = elem->head.mixer->private_data;
+
+	ucontrol->value.enumerated.item[0] = private->mux[elem->control];
+	return 0;
+}
+
+static int scarlett2_mux_src_enum_ctl_put(struct snd_kcontrol *kctl,
+					  struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct usb_mixer_interface *mixer = elem->head.mixer;
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	int index = elem->control;
+	int oval, val, err = 0;
+
+	mutex_lock(&private->data_mutex);
+
+	oval = private->mux[index];
+	val = clamp(ucontrol->value.integer.value[0],
+		    0L, private->num_mux_srcs - 1L);
+
+	if (oval == val)
+		goto unlock;
+
+	private->mux[index] = val;
+	err = scarlett2_usb_set_mux(mixer);
+	if (err == 0)
+		err = 1;
+
+unlock:
+	mutex_unlock(&private->data_mutex);
+	return err;
+}
+
+static const struct snd_kcontrol_new scarlett2_mux_src_enum_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.name = "",
+	.info = scarlett2_mux_src_enum_ctl_info,
+	.get  = scarlett2_mux_src_enum_ctl_get,
+	.put  = scarlett2_mux_src_enum_ctl_put,
+};
+
+static int scarlett2_add_mux_enums(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_ports *ports = private->info->ports;
+	int port_type, channel, i;
+
+	for (i = 0, port_type = 0;
+	     port_type < SCARLETT2_PORT_TYPE_COUNT;
+	     port_type++) {
+		for (channel = 0;
+		     channel < ports[port_type].num[SCARLETT2_PORT_OUT];
+		     channel++, i++) {
+			int err;
+			char s[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+			const char *const descr = ports[port_type].dst_descr;
+
+			snprintf(s, sizeof(s) - 5, descr, channel + 1);
+			strcat(s, " Enum");
+
+			err = scarlett2_add_new_ctl(mixer,
+						    &scarlett2_mux_src_enum_ctl,
+						    i, 1, s, NULL);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	return 0;
+}
+
+/*** Meter Controls ***/
+
+static int scarlett2_meter_ctl_info(struct snd_kcontrol *kctl,
+				    struct snd_ctl_elem_info *uinfo)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = elem->channels;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = 4095;
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int scarlett2_meter_ctl_get(struct snd_kcontrol *kctl,
+				   struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	u16 meter_levels[SCARLETT2_NUM_METERS];
+	int i, err;
+
+	err = scarlett2_usb_get_meter_levels(elem->head.mixer, meter_levels);
+	if (err < 0)
+		return err;
+
+	for (i = 0; i < elem->channels; i++)
+		ucontrol->value.integer.value[i] = meter_levels[i];
+
+	return 0;
+}
+
+static const struct snd_kcontrol_new scarlett2_meter_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_PCM,
+	.access = SNDRV_CTL_ELEM_ACCESS_READ | SNDRV_CTL_ELEM_ACCESS_VOLATILE,
+	.name = "",
+	.info = scarlett2_meter_ctl_info,
+	.get  = scarlett2_meter_ctl_get
+};
+
+static int scarlett2_add_meter_ctl(struct usb_mixer_interface *mixer)
+{
+	return scarlett2_add_new_ctl(mixer, &scarlett2_meter_ctl,
+				     0, SCARLETT2_NUM_METERS,
+				     "Level Meter", NULL);
+}
+
+/*** Initialisation ***/
+
+static int scarlett2_count_mux_srcs(const struct scarlett2_ports *ports)
+{
+	int port_type, count = 0;
+
+	for (port_type = 0;
+	     port_type < SCARLETT2_PORT_TYPE_COUNT;
+	     port_type++)
+		count += ports[port_type].num[SCARLETT2_PORT_IN];
+
+	return count;
+}
+
+/* Default routing connects PCM outputs and inputs to Analogue,
+ * S/PDIF, then ADAT
+ */
+static void scarlett2_init_routing(u8 *mux,
+				   const struct scarlett2_ports *ports)
+{
+	int i, input_num, input_count, port_type;
+	int output_num, output_count, port_type_connect_num;
+
+	static const int connect_order[] = {
+		SCARLETT2_PORT_TYPE_ANALOGUE,
+		SCARLETT2_PORT_TYPE_SPDIF,
+		SCARLETT2_PORT_TYPE_ADAT,
+		-1
+	};
+
+	/* Assign PCM inputs (routing outputs) */
+	output_num = scarlett2_get_port_start_num(ports,
+						  SCARLETT2_PORT_OUT,
+						  SCARLETT2_PORT_TYPE_PCM);
+	output_count = ports[SCARLETT2_PORT_TYPE_PCM].num[SCARLETT2_PORT_OUT];
+
+	for (port_type = connect_order[port_type_connect_num = 0];
+	     port_type >= 0;
+	     port_type = connect_order[++port_type_connect_num]) {
+		input_num = scarlett2_get_port_start_num(
+			ports, SCARLETT2_PORT_IN, port_type);
+		input_count = ports[port_type].num[SCARLETT2_PORT_IN];
+		for (i = 0;
+		     i < input_count && output_count;
+		     i++, output_count--)
+			mux[output_num++] = input_num++;
+	}
+
+	/* Assign PCM outputs (routing inputs) */
+	input_num = scarlett2_get_port_start_num(ports,
+						 SCARLETT2_PORT_IN,
+						 SCARLETT2_PORT_TYPE_PCM);
+	input_count = ports[SCARLETT2_PORT_TYPE_PCM].num[SCARLETT2_PORT_IN];
+
+	for (port_type = connect_order[port_type_connect_num = 0];
+	     port_type >= 0;
+	     port_type = connect_order[++port_type_connect_num]) {
+		output_num = scarlett2_get_port_start_num(
+			ports, SCARLETT2_PORT_OUT, port_type);
+		output_count = ports[port_type].num[SCARLETT2_PORT_OUT];
+		for (i = 0;
+		     i < output_count && input_count;
+		     i++, input_count--)
+			mux[output_num++] = input_num++;
+	}
+}
+
+/* Initialise private data, routing, sequence number */
+static int scarlett2_init_private(struct usb_mixer_interface *mixer,
+				  const struct scarlett2_device_info *info)
+{
+	struct scarlett2_mixer_data *private =
+		kzalloc(sizeof(struct scarlett2_mixer_data), GFP_KERNEL);
+
+	if (!private)
+		return -ENOMEM;
+
+	mutex_init(&private->usb_mutex);
+	mutex_init(&private->data_mutex);
+	INIT_DELAYED_WORK(&private->work, scarlett2_config_save);
+	private->info = info;
+	private->num_mux_srcs = scarlett2_count_mux_srcs(info->ports);
+	private->scarlett2_seq = 0;
+	private->mixer = mixer;
+	mixer->private_data = private;
+	mixer->private_free = snd_scarlett_gen2_private_free;
+
+	/* Setup default routing */
+	scarlett2_init_routing(private->mux, info->ports);
+
+	/* Initialise the sequence number used for the proprietary commands */
+	return scarlett2_usb(mixer, SCARLETT2_USB_INIT_SEQ,
+			     NULL, 0, NULL, 0);
+}
+
+/* Read line-in config and line-out volume settings on start */
+static int scarlett2_read_configs(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_device_info *info = private->info;
+	const struct scarlett2_ports *ports = info->ports;
+	int num_line_out =
+		ports[SCARLETT2_PORT_TYPE_ANALOGUE].num[SCARLETT2_PORT_OUT];
+	u8 level_switches[SCARLETT2_LEVEL_SWITCH_MAX];
+	u8 pad_switches[SCARLETT2_PAD_SWITCH_MAX];
+	struct scarlett2_usb_volume_status volume_status;
+	int err, i;
+
+	if (info->level_input_count) {
+		err = scarlett2_usb_get_config(
+			mixer,
+			SCARLETT2_CONFIG_LEVEL_SWITCH,
+			info->level_input_count,
+			level_switches);
+		if (err < 0)
+			return err;
+		for (i = 0; i < info->level_input_count; i++)
+			private->level_switch[i] = level_switches[i];
+	}
+
+	if (info->pad_input_count) {
+		err = scarlett2_usb_get_config(
+			mixer,
+			SCARLETT2_CONFIG_PAD_SWITCH,
+			info->pad_input_count,
+			pad_switches);
+		if (err < 0)
+			return err;
+		for (i = 0; i < info->pad_input_count; i++)
+			private->pad_switch[i] = pad_switches[i];
+	}
+
+	err = scarlett2_usb_get_volume_status(mixer, &volume_status);
+	if (err < 0)
+		return err;
+
+	private->master_vol = clamp(
+		volume_status.master_vol + SCARLETT_VOLUME_BIAS,
+		0, SCARLETT_VOLUME_BIAS);
+
+	for (i = 0; i < num_line_out; i++) {
+		int volume;
+
+		private->vol_sw_hw_switch[i] =
+			info->line_out_hw_vol
+				&& volume_status.sw_hw_switch[i];
+
+		volume = private->vol_sw_hw_switch[i]
+			   ? volume_status.master_vol
+			   : volume_status.sw_vol[i];
+		volume = clamp(volume + SCARLETT_VOLUME_BIAS,
+			       0, SCARLETT_VOLUME_BIAS);
+		private->vol[i] = volume;
+	}
+
+	for (i = 0; i < info->button_count; i++)
+		private->buttons[i] = !!volume_status.buttons[i];
+
+	return 0;
+}
+
+/* Notify on volume change */
+static void scarlett2_mixer_interrupt_vol_change(
+	struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	const struct scarlett2_ports *ports = private->info->ports;
+	int num_line_out =
+		ports[SCARLETT2_PORT_TYPE_ANALOGUE].num[SCARLETT2_PORT_OUT];
+	int i;
+
+	private->vol_updated = 1;
+
+	snd_ctl_notify(mixer->chip->card, SNDRV_CTL_EVENT_MASK_VALUE,
+		       &private->master_vol_ctl->id);
+
+	for (i = 0; i < num_line_out; i++) {
+		if (!private->vol_sw_hw_switch[i])
+			continue;
+		snd_ctl_notify(mixer->chip->card, SNDRV_CTL_EVENT_MASK_VALUE,
+			       &private->vol_ctls[i]->id);
+	}
+}
+
+/* Notify on button change */
+static void scarlett2_mixer_interrupt_button_change(
+	struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+	int i;
+
+	private->vol_updated = 1;
+
+	for (i = 0; i < private->info->button_count; i++)
+		snd_ctl_notify(mixer->chip->card, SNDRV_CTL_EVENT_MASK_VALUE,
+			       &private->button_ctls[i]->id);
+}
+
+/* Interrupt callback */
+static void scarlett2_mixer_interrupt(struct urb *urb)
+{
+	struct usb_mixer_interface *mixer = urb->context;
+	int len = urb->actual_length;
+	int ustatus = urb->status;
+	u32 data;
+
+	if (ustatus != 0)
+		goto requeue;
+
+	if (len == 8) {
+		data = le32_to_cpu(*(u32 *)urb->transfer_buffer);
+		if (data & SCARLETT2_USB_INTERRUPT_VOL_CHANGE)
+			scarlett2_mixer_interrupt_vol_change(mixer);
+		if (data & SCARLETT2_USB_INTERRUPT_BUTTON_CHANGE)
+			scarlett2_mixer_interrupt_button_change(mixer);
+	} else {
+		usb_audio_err(mixer->chip,
+			      "scarlett mixer interrupt length %d\n", len);
+	}
+
+requeue:
+	if (ustatus != -ENOENT &&
+	    ustatus != -ECONNRESET &&
+	    ustatus != -ESHUTDOWN) {
+		urb->dev = mixer->chip->dev;
+		usb_submit_urb(urb, GFP_ATOMIC);
+	}
+}
+
+static int scarlett2_mixer_status_create(struct usb_mixer_interface *mixer)
+{
+	void *transfer_buffer;
+
+	if (mixer->urb) {
+		usb_audio_err(mixer->chip,
+			      "%s: mixer urb already in use!\n", __func__);
+		return 0;
+	}
+
+	mixer->urb = usb_alloc_urb(0, GFP_KERNEL);
+	if (!mixer->urb)
+		return -ENOMEM;
+
+	transfer_buffer = kmalloc(SCARLETT2_USB_INTERRUPT_MAX_DATA, GFP_KERNEL);
+	if (!transfer_buffer)
+		return -ENOMEM;
+
+	usb_fill_int_urb(
+		mixer->urb,
+		mixer->chip->dev,
+		usb_rcvintpipe(mixer->chip->dev,
+			       SCARLETT2_USB_INTERRUPT_ENDPOINT),
+		transfer_buffer,
+		SCARLETT2_USB_INTERRUPT_MAX_DATA,
+		scarlett2_mixer_interrupt,
+		mixer,
+		SCARLETT2_USB_INTERRUPT_INTERVAL);
+
+	return usb_submit_urb(mixer->urb, GFP_KERNEL);
+}
+
+/* Entry point */
+int snd_scarlett_gen2_controls_create(struct usb_mixer_interface *mixer)
+{
+	const struct scarlett2_device_info *info;
+	int err;
+
+	/* only use UAC_VERSION_2 */
+	if (!mixer->protocol)
+		return 0;
+
+	switch (mixer->chip->usb_id) {
+	case USB_ID(0x1235, 0x8203):
+		info = &s6i6_gen2_info;
+		break;
+	case USB_ID(0x1235, 0x8204):
+		info = &s18i8_gen2_info;
+		break;
+	case USB_ID(0x1235, 0x8201):
+		info = &s18i20_gen2_info;
+		break;
+	default: /* device not (yet) supported */
+		return -EINVAL;
+	}
+
+	if (!scarlett_gen2_mixer_enable) {
+		usb_audio_err(mixer->chip,
+			"Focusrite Scarlett Gen 2 Mixer Driver disabled; use "
+			"options snd_usb_audio scarlett_gen2_mixer_enable=1 "
+			"to enable and report any issues to g@b4.vu");
+		return 0;
+	}
+
+	/* Initialise private data, routing, sequence number */
+	err = scarlett2_init_private(mixer, info);
+	if (err < 0)
+		return err;
+
+	/* Read volume levels and controls from the interface */
+	err = scarlett2_read_configs(mixer);
+	if (err < 0)
+		return err;
+
+	/* Create the analogue output controls */
+	err = scarlett2_add_line_out_ctls(mixer);
+	if (err < 0)
+		return err;
+
+	/* Create the analogue input controls */
+	err = scarlett2_add_line_in_ctls(mixer);
+	if (err < 0)
+		return err;
+
+	/* Create the input, output, and mixer mux input selections */
+	err = scarlett2_add_mux_enums(mixer);
+	if (err < 0)
+		return err;
+
+	/* Create the matrix mixer controls */
+	err = scarlett2_add_mixer_ctls(mixer);
+	if (err < 0)
+		return err;
+
+	/* Create the level meter controls */
+	err = scarlett2_add_meter_ctl(mixer);
+	if (err < 0)
+		return err;
+
+	/* Set up the interrupt polling if there are hardware buttons */
+	if (info->button_count) {
+		err = scarlett2_mixer_status_create(mixer);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+
+static void snd_scarlett_gen2_private_free(struct usb_mixer_interface *mixer)
+{
+	struct scarlett2_mixer_data *private = mixer->private_data;
+
+	cancel_delayed_work_sync(&private->work);
+	kfree(private);
+	mixer->private_data = NULL;
+}
diff --git a/sound/usb/mixer_scarlett_gen2.h b/sound/usb/mixer_scarlett_gen2.h
new file mode 100644
index 000000000000..52e1dad77afd
--- /dev/null
+++ b/sound/usb/mixer_scarlett_gen2.h
@@ -0,0 +1,7 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __USB_MIXER_SCARLETT_GEN2_H
+#define __USB_MIXER_SCARLETT_GEN2_H
+
+int snd_scarlett_gen2_controls_create(struct usb_mixer_interface *mixer);
+
+#endif /* __USB_MIXER_SCARLETT_GEN2_H */