diff mbox

[4/4,v6] ALSA: usb-audio: Scarlett mixer interface for 6i6, 18i6, 18i8 and 18i20

Message ID 1415645958-11488-5-git-send-email-chris.j.arges@canonical.com (mailing list archive)
State New, archived
Headers show

Commit Message

Chris J Arges Nov. 10, 2014, 6:59 p.m. UTC
This code contains the Scarlett mixer interface code that was originally
written by Tobias Hoffman and Robin Gareus. Because the device doesn't
properly implement UAC2 this code adds a mixer quirk for the device.

Changes from the original code include removing the metering code along with
dead code and comments. Compiler warnings were fixed. The code to initialize
the sampling rate was causing a crash this was fixed as discussed on the
mailing list. Error, and info messages were convered to dev_err and dev_info
interfaces. The custom scarlett_mixer_elem_info struct was replaced with the
more generic usb_mixer_elem_info to be able to recycle more code from mixer.c.

This patch also makes additional modifications based on upstream comments.
Individual control creation functions are removed and a generic
function is no used. Macros for function calls are removed to improve
readability. Hardcoded control initialization is removed. Save to HW
functionality has been removed. Strings for enums are created dynamically for
the mixer. Strings used for controls are now SNDRV_CTL_ELEM_ID_NAME_MAXLEN
length.

Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
---
 sound/usb/Makefile         |    1 +
 sound/usb/mixer_quirks.c   |    9 +
 sound/usb/mixer_scarlett.c | 1001 ++++++++++++++++++++++++++++++++++++++++++++
 sound/usb/mixer_scarlett.h |    6 +
 4 files changed, 1017 insertions(+)
 create mode 100644 sound/usb/mixer_scarlett.c
 create mode 100644 sound/usb/mixer_scarlett.h

Comments

Takashi Iwai Nov. 10, 2014, 7:24 p.m. UTC | #1
At Mon, 10 Nov 2014 12:59:18 -0600,
Chris J Arges wrote:
> 
> +/*
> + * Create enumeration strings from device_info
> + */
> +int scarlett_create_strings_from_info(struct scarlett_device_info *info)
> +{
> +	int i = 0, j = 0;

Superfluous initializations.


> +	char **names;
> +
> +	names = kmalloc_array(info->opt_master.len, sizeof(char *), GFP_KERNEL);
> +	if (!names) {
> +		kfree(names);

Superfluous kfree().

> +		return -ENOMEM;
> +	}
> +
> +	for (i = 0; i < info->opt_master.len; i++) {
> +		names[i] = kmalloc_array(SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
> +				   sizeof(char), GFP_KERNEL);

Just use kmalloc().

> +		if (!names[i]) {
> +			for (j = 0; j < i-1; j++)
> +				kfree(names[j]);
> +			kfree(names);
> +			return -ENOMEM;
> +		}
> +		if (i > info->mix_start) {
> +			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
> +				 "Mix %c", 'A'+(i - info->mix_start - 1));
> +		} else if (i > info->adat_start) {
> +			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
> +				 "ADAT %d", i - info->adat_start);
> +		} else if (i > info->spdif_start) {
> +			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
> +				 "SPDIF %d", i - info->spdif_start);
> +		} else if (i > info->analog_start) {
> +			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
> +				 "Analog %d", i - info->analog_start);
> +		} else if (i > info->pcm_start) {
> +			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
> +				 "PCM %d", i - info->pcm_start);
> +		} else {
> +			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
> +				 "Off");
> +		}

BTW, another way would be to use kasprintf() and directly assign to
names[i].  It'll save memory usage a bit.  Although this won't
guarantee the max length, but these strings are obviously short
enough, so no big worry about it.

But, it's really a small difference, so I don't mind either way.

However...

> +	}
> +
> +	/* assign to the appropriate control */
> +	info->opt_master.names = (const char * const *)names;
> +	info->opt_matrix.names = (const char * const *)names;

... I guess these will be leaked without destructor?  This has to be
fixed.  You need to add a flag indicating the need of kfree() and do
it in the own destructor accordingly.


thanks,

Takashi
Chris J Arges Nov. 10, 2014, 10 p.m. UTC | #2
<snip>
> However...
> 
>> +	}
>> +
>> +	/* assign to the appropriate control */
>> +	info->opt_master.names = (const char * const *)names;
>> +	info->opt_matrix.names = (const char * const *)names;
> 
> ... I guess these will be leaked without destructor?  This has to be
> fixed.  You need to add a flag indicating the need of kfree() and do
> it in the own destructor accordingly.
> 
> 
> thanks,
> 
> Takashi
> 
Where is the best place for this destructor?

At the end of the snd_scarlett_controls_create function doesn't work due
to opt_*.names being referenced by scarlett_ctl_enum_info afterwards.

Creating a custom private_free callback doesn't seem correct either as I
should only need to free the memory once and not repeatedly. However
with a flag I could check and only free once on the callback.

Thanks,
--chris
Takashi Iwai Nov. 11, 2014, 7:33 a.m. UTC | #3
At Mon, 10 Nov 2014 16:00:17 -0600,
Chris J Arges wrote:
> 
> <snip>
> > However...
> > 
> >> +	}
> >> +
> >> +	/* assign to the appropriate control */
> >> +	info->opt_master.names = (const char * const *)names;
> >> +	info->opt_matrix.names = (const char * const *)names;
> > 
> > ... I guess these will be leaked without destructor?  This has to be
> > fixed.  You need to add a flag indicating the need of kfree() and do
> > it in the own destructor accordingly.
> > 
> > 
> > thanks,
> > 
> > Takashi
> > 
> Where is the best place for this destructor?
> 
> At the end of the snd_scarlett_controls_create function doesn't work due
> to opt_*.names being referenced by scarlett_ctl_enum_info afterwards.
> 
> Creating a custom private_free callback doesn't seem correct either as I
> should only need to free the memory once and not repeatedly. However
> with a flag I could check and only free once on the callback.

Well, further looking at the code, it seems more buggy than I thought.
scarlett_create_strings_from_info() may override the existing pointer
that has been allocated.  Again this leaks.

So, in the end, the cleanest way would be to generate a string in the
info callback itself.  It doesn't need to allocate at all, it just
writes to uinfo->value.enumerated.name dynamically.


Takashi
Chris J Arges Nov. 12, 2014, 6:06 p.m. UTC | #4
This is v5 of the patchset to merge what Tobias Hoffman and Robin Gareus have
done to enable the Focusrite Scarlett mixers for use with ALSA.

[v3]

I have split the commits into hopefully a logical series. First the original
quirk is reverted for one model of a Scarlett device. Next an additional
structure is added to be able to more easily reuse usb_mixer_elem_info.
After this mixer functions that were useful to this code were made public.
Finally the last patch adds the necessary functions to make this mixer work.

[v4]

This version removes the per-mixer control creation functions and uses a
generic function based on structure data. Macros used for control addition
are removed and the plain function is used instead. Hardcoded text block is
removed and macros to define strings are used instead. Hardcoded control
initialization has been removed.

[v5]

In this version, HW saving functionality has been removed in this initial
patchset. Macros for function calls are removed for readability. Strings for
enums are created dynamically using the info structures. String lengths for
controls are now all SNDRV_CTL_ELEM_ID_NAME_MAXLEN in length.

[v6]

Removed dead variables. Made names const char * const * again. Adjusted
scarlett_ctl_enum_* functions to be a bit clearer. Used strlcpy where
appropriate. Properly free two dimensional array.

[v7]

Generate strings directly in enum_info function instead of dynamically
allocating into another array and copying. Remove unnecessary initializations,
kfrees and use kmalloc instead of kmalloc_array. Update comments to reflect
current mixer functionality.

Chris J Arges (4):
  Revert "ALSA: usb-audio: Add quirk for Focusrite Scarlett
  ALSA: usb-audio: Add private_data pointer to usb_mixer_elem_info
  ALSA: usb-audio: make set_*_mix_values functions public
  ALSA: usb-audio: Scarlett mixer interface for 6i6, 18i6, 18i8 and
    18i20

 sound/usb/Makefile         |    1 +
 sound/usb/mixer.c          |   34 +-
 sound/usb/mixer.h          |    9 +
 sound/usb/mixer_quirks.c   |   18 +-
 sound/usb/mixer_scarlett.c | 1001 ++++++++++++++++++++++++++++++++++++++++++++
 sound/usb/mixer_scarlett.h |    6 +
 sound/usb/quirks-table.h   |   51 ---
 7 files changed, 1044 insertions(+), 76 deletions(-)
 create mode 100644 sound/usb/mixer_scarlett.c
 create mode 100644 sound/usb/mixer_scarlett.h
Takashi Iwai Nov. 13, 2014, 6:36 a.m. UTC | #5
At Wed, 12 Nov 2014 12:06:58 -0600,
Chris J Arges wrote:
> 
> This is v5 of the patchset to merge what Tobias Hoffman and Robin Gareus have
> done to enable the Focusrite Scarlett mixers for use with ALSA.

Already v7? :)

I applied the patch series now to for-next branch.
If anything is missing, let's fix on top of that.


thanks,

Takashi


> 
> [v3]
> 
> I have split the commits into hopefully a logical series. First the original
> quirk is reverted for one model of a Scarlett device. Next an additional
> structure is added to be able to more easily reuse usb_mixer_elem_info.
> After this mixer functions that were useful to this code were made public.
> Finally the last patch adds the necessary functions to make this mixer work.
> 
> [v4]
> 
> This version removes the per-mixer control creation functions and uses a
> generic function based on structure data. Macros used for control addition
> are removed and the plain function is used instead. Hardcoded text block is
> removed and macros to define strings are used instead. Hardcoded control
> initialization has been removed.
> 
> [v5]
> 
> In this version, HW saving functionality has been removed in this initial
> patchset. Macros for function calls are removed for readability. Strings for
> enums are created dynamically using the info structures. String lengths for
> controls are now all SNDRV_CTL_ELEM_ID_NAME_MAXLEN in length.
> 
> [v6]
> 
> Removed dead variables. Made names const char * const * again. Adjusted
> scarlett_ctl_enum_* functions to be a bit clearer. Used strlcpy where
> appropriate. Properly free two dimensional array.
> 
> [v7]
> 
> Generate strings directly in enum_info function instead of dynamically
> allocating into another array and copying. Remove unnecessary initializations,
> kfrees and use kmalloc instead of kmalloc_array. Update comments to reflect
> current mixer functionality.
> 
> Chris J Arges (4):
>   Revert "ALSA: usb-audio: Add quirk for Focusrite Scarlett
>   ALSA: usb-audio: Add private_data pointer to usb_mixer_elem_info
>   ALSA: usb-audio: make set_*_mix_values functions public
>   ALSA: usb-audio: Scarlett mixer interface for 6i6, 18i6, 18i8 and
>     18i20
> 
>  sound/usb/Makefile         |    1 +
>  sound/usb/mixer.c          |   34 +-
>  sound/usb/mixer.h          |    9 +
>  sound/usb/mixer_quirks.c   |   18 +-
>  sound/usb/mixer_scarlett.c | 1001 ++++++++++++++++++++++++++++++++++++++++++++
>  sound/usb/mixer_scarlett.h |    6 +
>  sound/usb/quirks-table.h   |   51 ---
>  7 files changed, 1044 insertions(+), 76 deletions(-)
>  create mode 100644 sound/usb/mixer_scarlett.c
>  create mode 100644 sound/usb/mixer_scarlett.h
> 
> -- 
> 2.1.3
>
David Henningsson Nov. 13, 2014, 6:38 a.m. UTC | #6
On 2014-11-13 07:36, Takashi Iwai wrote:
> At Wed, 12 Nov 2014 12:06:58 -0600,
> Chris J Arges wrote:
>>
>> This is v5 of the patchset to merge what Tobias Hoffman and Robin Gareus have
>> done to enable the Focusrite Scarlett mixers for use with ALSA.
>
> Already v7? :)
>
> I applied the patch series now to for-next branch.
> If anything is missing, let's fix on top of that.

\o/

Excellent, thanks to all of you for bringing better hardware support to 
Linux! :-)
Chris J Arges Nov. 13, 2014, 1:01 p.m. UTC | #7
On 11/13/2014 12:36 AM, Takashi Iwai wrote:
> At Wed, 12 Nov 2014 12:06:58 -0600,
> Chris J Arges wrote:
>>
>> This is v5 of the patchset to merge what Tobias Hoffman and Robin Gareus have
>> done to enable the Focusrite Scarlett mixers for use with ALSA.
> 
> Already v7? :)
> 
> I applied the patch series now to for-next branch.
> If anything is missing, let's fix on top of that.
> 
> 
> thanks,
> 
> Takashi
> 
Takashi,
Thank you for your patience and help reviewing and applying this.
--chris j arges



> 
>>
>> [v3]
>>
>> I have split the commits into hopefully a logical series. First the original
>> quirk is reverted for one model of a Scarlett device. Next an additional
>> structure is added to be able to more easily reuse usb_mixer_elem_info.
>> After this mixer functions that were useful to this code were made public.
>> Finally the last patch adds the necessary functions to make this mixer work.
>>
>> [v4]
>>
>> This version removes the per-mixer control creation functions and uses a
>> generic function based on structure data. Macros used for control addition
>> are removed and the plain function is used instead. Hardcoded text block is
>> removed and macros to define strings are used instead. Hardcoded control
>> initialization has been removed.
>>
>> [v5]
>>
>> In this version, HW saving functionality has been removed in this initial
>> patchset. Macros for function calls are removed for readability. Strings for
>> enums are created dynamically using the info structures. String lengths for
>> controls are now all SNDRV_CTL_ELEM_ID_NAME_MAXLEN in length.
>>
>> [v6]
>>
>> Removed dead variables. Made names const char * const * again. Adjusted
>> scarlett_ctl_enum_* functions to be a bit clearer. Used strlcpy where
>> appropriate. Properly free two dimensional array.
>>
>> [v7]
>>
>> Generate strings directly in enum_info function instead of dynamically
>> allocating into another array and copying. Remove unnecessary initializations,
>> kfrees and use kmalloc instead of kmalloc_array. Update comments to reflect
>> current mixer functionality.
>>
>> Chris J Arges (4):
>>   Revert "ALSA: usb-audio: Add quirk for Focusrite Scarlett
>>   ALSA: usb-audio: Add private_data pointer to usb_mixer_elem_info
>>   ALSA: usb-audio: make set_*_mix_values functions public
>>   ALSA: usb-audio: Scarlett mixer interface for 6i6, 18i6, 18i8 and
>>     18i20
>>
>>  sound/usb/Makefile         |    1 +
>>  sound/usb/mixer.c          |   34 +-
>>  sound/usb/mixer.h          |    9 +
>>  sound/usb/mixer_quirks.c   |   18 +-
>>  sound/usb/mixer_scarlett.c | 1001 ++++++++++++++++++++++++++++++++++++++++++++
>>  sound/usb/mixer_scarlett.h |    6 +
>>  sound/usb/quirks-table.h   |   51 ---
>>  7 files changed, 1044 insertions(+), 76 deletions(-)
>>  create mode 100644 sound/usb/mixer_scarlett.c
>>  create mode 100644 sound/usb/mixer_scarlett.h
>>
>> -- 
>> 2.1.3
>>
>
diff mbox

Patch

diff --git a/sound/usb/Makefile b/sound/usb/Makefile
index 2b92f0d..bcee406 100644
--- a/sound/usb/Makefile
+++ b/sound/usb/Makefile
@@ -9,6 +9,7 @@  snd-usb-audio-objs := 	card.o \
 			helper.o \
 			mixer.o \
 			mixer_quirks.o \
+			mixer_scarlett.o \
 			pcm.o \
 			proc.o \
 			quirks.o \
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index c9665bf..d06d27a 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -41,6 +41,7 @@ 
 #include "usbaudio.h"
 #include "mixer.h"
 #include "mixer_quirks.h"
+#include "mixer_scarlett.h"
 #include "helper.h"
 
 extern struct snd_kcontrol_new *snd_usb_feature_unit_ctl;
@@ -1664,6 +1665,14 @@  int snd_usb_mixer_apply_create_quirk(struct usb_mixer_interface *mixer)
 		/* detection is disabled in mixer_maps.c */
 		err = snd_create_std_mono_table(mixer, ebox44_table);
 		break;
+
+	case USB_ID(0x1235, 0x8012): /* Focusrite Scarlett 6i6 */
+	case USB_ID(0x1235, 0x8002): /* Focusrite Scarlett 8i6 */
+	case USB_ID(0x1235, 0x8004): /* Focusrite Scarlett 18i6 */
+	case USB_ID(0x1235, 0x8014): /* Focusrite Scarlett 18i8 */
+	case USB_ID(0x1235, 0x800c): /* Focusrite Scarlett 18i20 */
+		err = snd_scarlett_controls_create(mixer);
+		break;
 	}
 
 	return err;
diff --git a/sound/usb/mixer_scarlett.c b/sound/usb/mixer_scarlett.c
new file mode 100644
index 0000000..a1bb0f6
--- /dev/null
+++ b/sound/usb/mixer_scarlett.c
@@ -0,0 +1,1001 @@ 
+/*
+ *   Scarlett 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.
+ *
+ */
+
+/*
+ * Rewritten and extended to support more models, e.g. Scarlett 18i8.
+ *
+ * Many features of Scarlett 18i6 do not lend themselves to be implemented
+ * as simple mixer-quirk -- or at least I don't see a way how to do that, yet.
+ * Hence the top parts of this file is a 1:1 copy of select static functions
+ * from mixer.c to implement the interface.
+ * Suggestions how to avoid this code duplication are very welcome.
+ *
+ * eventually this should either be integrated as quirk into mixer_quirks.c
+ * or become a standalone module.
+ *
+ * This source hardcodes the URBs for the Scarlett,
+ * Auto-detection via UAC2 is not feasible to properly discover the vast
+ * majority of features. It's related to both Linux/ALSA's UAC2 as well as
+ * Focusrite's implementation of it. Eventually quirks may be sufficient but
+ * right now it's a major headache to work arount these things.
+ *
+ * NB. Neither the OSX nor the win driver provided by Focusrite performs
+ * discovery, they seem to operate the same as this driver.
+ */
+
+/* Mixer Interface for the Focusrite Scarlett 18i6 audio interface.
+ *
+ * The protocol was reverse engineered by looking at communication between
+ * Scarlett MixControl (v 1.2.128.0) and the Focusrite(R) Scarlett 18i6
+ * (firmware v305) using wireshark and usbmon in January 2013.
+ * Extended in July 2013.
+ *
+ * this mixer gives complete access to all features of the device:
+ *  - change Impedance of inputs (Line-in, Mic / Instrument, Hi-Z)
+ *  - select clock source
+ *  - dynamic input to mixer-matrix assignment
+ *  - 18 x 6 mixer-matrix gain stages
+ *  - bus routing & volume control
+ *  - save setting to hardware
+ *  - automatic re-initialization on connect if device was power-cycled
+ *  - peak monitoring of all 3 buses (18 input, 6 DAW input, 6 route channels)
+ *  (changing the samplerate and buffersize is supported by the PCM interface)
+ *
+ *
+ * USB URB commands overview (bRequest = 0x01 = UAC2_CS_CUR)
+ * wIndex
+ * 0x01 Analog Input line/instrument impedance switch, wValue=0x0901 +
+ *      channel, data=Line/Inst (2bytes)
+ *      pad (-10dB) switch, wValue=0x0b01 + channel, data=Off/On (2bytes)
+ *      ?? wValue=0x0803/04, ?? (2bytes)
+ * 0x0a Master Volume, wValue=0x0200+bus[0:all + only 1..4?] data(2bytes)
+ *      Bus Mute/Unmute wValue=0x0100+bus[0:all + only 1..4?], data(2bytes)
+ * 0x28 Clock source, wValue=0x0100, data={1:int,2:spdif,3:adat} (1byte)
+ * 0x29 Set Sample-rate, wValue=0x0100, data=sample-rate(4bytes)
+ * 0x32 Mixer mux, wValue=0x0600 + mixer-channel, data=input-to-connect(2bytes)
+ * 0x33 Output mux, wValue=bus, data=input-to-connect(2bytes)
+ * 0x34 Capture mux, wValue=0...18, data=input-to-connect(2bytes)
+ * 0x3c Matrix Mixer gains, wValue=mixer-node  data=gain(2bytes)
+ *      ?? [sometimes](4bytes, e.g 0x000003be 0x000003bf ...03ff)
+ *
+ * USB reads: (i.e. actually issued by original software)
+ * 0x01 wValue=0x0901+channel (1byte!!), wValue=0x0b01+channed (1byte!!)
+ * 0x29 wValue=0x0100 sample-rate(4bytes)
+ *      wValue=0x0200 ?? 1byte (only once)
+ * 0x2a wValue=0x0100 ?? 4bytes, sample-rate2 ??
+ *
+ * USB reads with bRequest = 0x03 = UAC2_CS_MEM
+ * 0x3c wValue=0x0002 1byte: sync status (locked=1)
+ *      wValue=0x0000 18*2byte: peak meter (inputs)
+ *      wValue=0x0001 8(?)*2byte: peak meter (mix)
+ *      wValue=0x0003 6*2byte: peak meter (pcm/daw)
+ *
+ * USB write with bRequest = 0x03
+ * 0x3c Save settings to hardware: wValue=0x005a, data=0xa5
+ *
+ *
+ * <ditaa>
+ *  /--------------\    18chn            6chn    /--------------\
+ *  | Hardware  in +--+-------\        /------+--+ ALSA PCM out |
+ *  \--------------/  |       |        |      |  \--------------/
+ *                    |       |        |      |
+ *                    |       v        v      |
+ *                    |   +---------------+   |
+ *                    |    \ Matrix  Mux /    |
+ *                    |     +-----+-----+     |
+ *                    |           |           |
+ *                    |           | 18chn     |
+ *                    |           v           |
+ *                    |     +-----------+     |
+ *                    |     | Mixer     |     |
+ *                    |     |    Matrix |     |
+ *                    |     |           |     |
+ *                    |     | 18x6 Gain |     |
+ *                    |     |   stages  |     |
+ *                    |     +-----+-----+     |
+ *                    |           |           |
+ *                    |           |           |
+ *                    | 18chn     | 6chn      | 6chn
+ *                    v           v           v
+ *                    =========================
+ *             +---------------+     +--—------------+
+ *              \ Output  Mux /       \ Capture Mux /
+ *               +-----+-----+         +-----+-----+
+ *                     |                     |
+ *                     | 6chn                |
+ *                     v                     |
+ *              +-------------+              |
+ *              | Master Gain |              |
+ *              +------+------+              |
+ *                     |                     |
+ *                     | 6chn                | 18chn
+ *                     | (3 stereo pairs)    |
+ *  /--------------\   |                     |   /--------------\
+ *  | Hardware out |<--/                     \-->| ALSA PCM  in |
+ *  \--------------/                             \--------------/
+ * </ditaa>
+ *
+ */
+
+#include <linux/slab.h>
+#include <linux/usb.h>
+#include <linux/usb/audio-v2.h>
+
+#include <sound/core.h>
+#include <sound/control.h>
+#include <sound/tlv.h>
+
+#include "usbaudio.h"
+#include "mixer.h"
+#include "helper.h"
+#include "power.h"
+
+#include "mixer_scarlett.h"
+
+/* some gui mixers can't handle negative ctl values */
+#define SND_SCARLETT_LEVEL_BIAS 128
+#define SND_SCARLETT_MATRIX_IN_MAX 18
+#define SND_SCARLETT_CONTROLS_MAX 10
+
+enum {
+	SCARLETT_OUTPUTS,
+	SCARLETT_SWITCH_IMPEDANCE,
+	SCARLETT_SWITCH_PAD,
+};
+
+struct scarlett_mixer_elem_enum_info {
+	int start;
+	int len;
+	char const * const *names;
+};
+
+struct scarlett_mixer_control {
+	unsigned char num;
+	unsigned char type;
+	const char *name;
+};
+
+struct scarlett_device_info {
+	int matrix_in;
+	int matrix_out;
+	int input_len;
+	int output_len;
+
+	int pcm_start;
+	int analog_start;
+	int spdif_start;
+	int adat_start;
+	int mix_start;
+
+	struct scarlett_mixer_elem_enum_info opt_master;
+	struct scarlett_mixer_elem_enum_info opt_matrix;
+
+	int matrix_mux_init[SND_SCARLETT_MATRIX_IN_MAX];
+
+	int num_controls;	/* number of items in controls */
+	const struct scarlett_mixer_control controls[SND_SCARLETT_CONTROLS_MAX];
+};
+
+/********************** Enum Strings *************************/
+
+static const struct scarlett_mixer_elem_enum_info opt_pad = {
+	.start = 0,
+	.len = 2,
+	.names = (char const * const []){
+		"0dB", "-10dB"
+	}
+};
+
+static const struct scarlett_mixer_elem_enum_info opt_impedance = {
+	.start = 0,
+	.len = 2,
+	.names = (char const * const []){
+		"Line", "Hi-Z"
+	}
+};
+
+static const struct scarlett_mixer_elem_enum_info opt_clock = {
+	.start = 1,
+	.len = 3,
+	.names = (char const * const []){
+		"Internal", "SPDIF", "ADAT"
+	}
+};
+
+static const struct scarlett_mixer_elem_enum_info opt_sync = {
+	.start = 0,
+	.len = 2,
+	.names = (char const * const []){
+		"No Lock", "Locked"
+	}
+};
+
+static int scarlett_ctl_switch_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_BOOLEAN;
+	uinfo->count = elem->channels;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = 1;
+	return 0;
+}
+
+static int scarlett_ctl_switch_get(struct snd_kcontrol *kctl,
+		struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	int i, err, val;
+
+	for (i = 0; i < elem->channels; i++) {
+		err = snd_usb_get_cur_mix_value(elem, i, i, &val);
+		if (err < 0)
+			return err;
+
+		val = !val; /* invert mute logic for mixer */
+		ucontrol->value.integer.value[i] = val;
+	}
+
+	return 0;
+}
+
+static int scarlett_ctl_switch_put(struct snd_kcontrol *kctl,
+		struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	int i, changed = 0;
+	int err, oval, val;
+
+	for (i = 0; i < elem->channels; i++) {
+		err = snd_usb_get_cur_mix_value(elem, i, i, &oval);
+		if (err < 0)
+			return err;
+
+		val = ucontrol->value.integer.value[i];
+		val = !val;
+		if (oval != val) {
+			err = snd_usb_set_cur_mix_value(elem, i, i, val);
+			if (err < 0)
+				return err;
+
+			changed = 1;
+		}
+	}
+
+	return changed;
+}
+
+static int scarlett_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 = (int)kctl->private_value +
+		SND_SCARLETT_LEVEL_BIAS;
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int scarlett_ctl_get(struct snd_kcontrol *kctl,
+			    struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	int i, err, val;
+
+	for (i = 0; i < elem->channels; i++) {
+		err = snd_usb_get_cur_mix_value(elem, i, i, &val);
+		if (err < 0)
+			return err;
+
+		val = clamp(val / 256, -128, (int)kctl->private_value) +
+				    SND_SCARLETT_LEVEL_BIAS;
+		ucontrol->value.integer.value[i] = val;
+	}
+
+	return 0;
+}
+
+static int scarlett_ctl_put(struct snd_kcontrol *kctl,
+			    struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	int i, changed = 0;
+	int err, oval, val;
+
+	for (i = 0; i < elem->channels; i++) {
+		err = snd_usb_get_cur_mix_value(elem, i, i, &oval);
+		if (err < 0)
+			return err;
+
+		val = ucontrol->value.integer.value[i] -
+			SND_SCARLETT_LEVEL_BIAS;
+		val = val * 256;
+		if (oval != val) {
+			err = snd_usb_set_cur_mix_value(elem, i, i, val);
+			if (err < 0)
+				return err;
+
+			changed = 1;
+		}
+	}
+
+	return changed;
+}
+
+static int scarlett_ctl_enum_info(struct snd_kcontrol *kctl,
+				  struct snd_ctl_elem_info *uinfo)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett_mixer_elem_enum_info *opt = elem->private_data;
+
+	return snd_ctl_enum_info(uinfo, elem->channels, opt->len,
+				 (const char * const *)opt->names);
+}
+
+static int scarlett_ctl_enum_get(struct snd_kcontrol *kctl,
+				 struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett_mixer_elem_enum_info *opt = elem->private_data;
+	int err, val;
+
+	err = snd_usb_get_cur_mix_value(elem, 0, 0, &val);
+	if (err < 0)
+		return err;
+
+	val = clamp(val - opt->start, 0, opt->len-1);
+
+	ucontrol->value.enumerated.item[0] = val;
+
+	return 0;
+}
+
+static int scarlett_ctl_enum_put(struct snd_kcontrol *kctl,
+				 struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct scarlett_mixer_elem_enum_info *opt = elem->private_data;
+	int err, oval, val;
+
+	err = snd_usb_get_cur_mix_value(elem, 0, 0, &oval);
+	if (err < 0)
+		return err;
+
+	val = ucontrol->value.integer.value[0];
+	val = val + opt->start;
+	if (val != oval) {
+		snd_usb_set_cur_mix_value(elem, 0, 0, val);
+		return 1;
+	}
+	return 0;
+}
+
+static int scarlett_ctl_meter_get(struct snd_kcontrol *kctl,
+				  struct snd_ctl_elem_value *ucontrol)
+{
+	struct usb_mixer_elem_info *elem = kctl->private_data;
+	struct snd_usb_audio *chip = elem->mixer->chip;
+	unsigned char buf[2 * MAX_CHANNELS] = {0, };
+	int wValue = (elem->control << 8) | elem->idx_off;
+	int idx = snd_usb_ctrl_intf(chip) | (elem->id << 8);
+	int err;
+
+	err = snd_usb_ctl_msg(chip->dev,
+				usb_rcvctrlpipe(chip->dev, 0),
+				UAC2_CS_MEM,
+				USB_RECIP_INTERFACE | USB_TYPE_CLASS |
+				USB_DIR_IN, wValue, idx, buf, elem->channels);
+	if (err < 0)
+		return err;
+
+	ucontrol->value.enumerated.item[0] = clamp((int)buf[0], 0, 1);
+	return 0;
+}
+
+static struct snd_kcontrol_new usb_scarlett_ctl_switch = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.name = "",
+	.info = scarlett_ctl_switch_info,
+	.get =  scarlett_ctl_switch_get,
+	.put =  scarlett_ctl_switch_put,
+};
+
+static const DECLARE_TLV_DB_SCALE(db_scale_scarlett_gain, -12800, 100, 0);
+
+static struct snd_kcontrol_new usb_scarlett_ctl = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+		  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+	.name = "",
+	.info = scarlett_ctl_info,
+	.get =  scarlett_ctl_get,
+	.put =  scarlett_ctl_put,
+	.private_value = 6,  /* max value */
+	.tlv = { .p = db_scale_scarlett_gain }
+};
+
+static struct snd_kcontrol_new usb_scarlett_ctl_master = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+		  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+	.name = "",
+	.info = scarlett_ctl_info,
+	.get =  scarlett_ctl_get,
+	.put =  scarlett_ctl_put,
+	.private_value = 6,  /* max value */
+	.tlv = { .p = db_scale_scarlett_gain }
+};
+
+static struct snd_kcontrol_new usb_scarlett_ctl_enum = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.name = "",
+	.info = scarlett_ctl_enum_info,
+	.get =  scarlett_ctl_enum_get,
+	.put =  scarlett_ctl_enum_put,
+};
+
+static struct snd_kcontrol_new usb_scarlett_ctl_sync = {
+	.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+	.access = SNDRV_CTL_ELEM_ACCESS_READ | SNDRV_CTL_ELEM_ACCESS_VOLATILE,
+	.name = "",
+	.info = scarlett_ctl_enum_info,
+	.get =  scarlett_ctl_meter_get,
+};
+
+static int add_new_ctl(struct usb_mixer_interface *mixer,
+		       const struct snd_kcontrol_new *ncontrol,
+		       int index, int offset, int num,
+		       int val_type, int channels, const char *name,
+		       const struct scarlett_mixer_elem_enum_info *opt,
+		       struct usb_mixer_elem_info **elem_ret
+)
+{
+	struct snd_kcontrol *kctl;
+	struct usb_mixer_elem_info *elem;
+	int err;
+
+	elem = kzalloc(sizeof(*elem), GFP_KERNEL);
+	if (!elem)
+		return -ENOMEM;
+
+	elem->mixer = mixer;
+	elem->control = offset;
+	elem->idx_off = num;
+	elem->id = index;
+	elem->val_type = val_type;
+
+	elem->channels = channels;
+
+	/* add scarlett_mixer_elem_enum_info struct */
+	elem->private_data = (void *)opt;
+
+	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_ctl_add(mixer->chip->card, kctl);
+	if (err < 0)
+		return err;
+
+	if (elem_ret)
+		*elem_ret = elem;
+
+	return 0;
+}
+
+static int add_output_ctls(struct usb_mixer_interface *mixer,
+			   int index, const char *name,
+			   const struct scarlett_device_info *info)
+{
+	int err;
+	char mx[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+	struct usb_mixer_elem_info *elem;
+
+	/* Add mute switch */
+	snprintf(mx, sizeof(mx), "Master %d (%s) Playback Switch",
+		index + 1, name);
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_switch, 0x0a, 0x01,
+			  2*index+1, USB_MIXER_S16, 2, mx, NULL, &elem);
+	if (err < 0)
+		return err;
+
+	/* Add volume control and initialize to 0 */
+	snprintf(mx, sizeof(mx), "Master %d (%s) Playback Volume",
+		index + 1, name);
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_master, 0x0a, 0x02,
+			  2*index+1, USB_MIXER_S16, 2, mx, NULL, &elem);
+	if (err < 0)
+		return err;
+
+	/* Add L channel source playback enumeration */
+	snprintf(mx, sizeof(mx), "Master %dL (%s) Source Playback Enum",
+		index + 1, name);
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_enum, 0x33, 0x00, 2*index,
+			  USB_MIXER_S16, 1, mx, &info->opt_master, &elem);
+	if (err < 0)
+		return err;
+
+	/* Add R channel source playback enumeration */
+	snprintf(mx, sizeof(mx), "Master %dR (%s) Source Playback Enum",
+		index + 1, name);
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_enum, 0x33, 0x00, 2*index+1,
+			  USB_MIXER_S16, 1, mx, &info->opt_master, &elem);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+/********************** device-specific config *************************/
+
+/*  untested...  */
+static struct scarlett_device_info s6i6_info = {
+	.matrix_in = 18,
+	.matrix_out = 8,
+	.input_len = 6,
+	.output_len = 6,
+
+	.pcm_start = 0,
+	.analog_start = 12,
+	.spdif_start = 16,
+	.adat_start = 18,
+	.mix_start = 18,
+
+	.opt_master = {
+		.start = -1,
+		.len = 27,
+		.names = NULL
+	},
+
+	.opt_matrix = {
+		.start = -1,
+		.len = 19,
+		.names = NULL
+	},
+
+	.num_controls = 0,
+	.controls = {
+		{ .num = 0, .type = SCARLETT_OUTPUTS, .name = "Monitor" },
+		{ .num = 1, .type = SCARLETT_OUTPUTS, .name = "Headphone" },
+		{ .num = 2, .type = SCARLETT_OUTPUTS, .name = "SPDIF" },
+		{ .num = 1, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 1, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 3, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 4, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+	},
+
+	.matrix_mux_init = {
+		12, 13, 14, 15,                 /* Analog -> 1..4 */
+		16, 17,                          /* SPDIF -> 5,6 */
+		0, 1, 2, 3, 4, 5, 6, 7,     /* PCM[1..12] -> 7..18 */
+		8, 9, 10, 11
+	}
+};
+
+/*  untested...  */
+static struct scarlett_device_info s8i6_info = {
+	.matrix_in = 18,
+	.matrix_out = 6,
+	.input_len = 8,
+	.output_len = 6,
+
+	.pcm_start = 0,
+	.analog_start = 12,
+	.spdif_start = 16,
+	.adat_start = 18,
+	.mix_start = 18,
+
+	.opt_master = {
+		.start = -1,
+		.len = 25,
+		.names = NULL
+	},
+
+	.opt_matrix = {
+		.start = -1,
+		.len = 19,
+		.names = NULL
+	},
+
+	.num_controls = 7,
+	.controls = {
+		{ .num = 0, .type = SCARLETT_OUTPUTS, .name = "Monitor" },
+		{ .num = 1, .type = SCARLETT_OUTPUTS, .name = "Headphone" },
+		{ .num = 2, .type = SCARLETT_OUTPUTS, .name = "SPDIF" },
+		{ .num = 1, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 3, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 4, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+	},
+
+	.matrix_mux_init = {
+		12, 13, 14, 15,                 /* Analog -> 1..4 */
+		16, 17,                          /* SPDIF -> 5,6 */
+		0, 1, 2, 3, 4, 5, 6, 7,     /* PCM[1..12] -> 7..18 */
+		8, 9, 10, 11
+	}
+};
+
+static struct scarlett_device_info s18i6_info = {
+	.matrix_in = 18,
+	.matrix_out = 6,
+	.input_len = 18,
+	.output_len = 6,
+
+	.pcm_start = 0,
+	.analog_start = 6,
+	.spdif_start = 14,
+	.adat_start = 16,
+	.mix_start = 24,
+
+	.opt_master = {
+		.start = -1,
+		.len = 31,
+		.names = NULL,
+	},
+
+	.opt_matrix = {
+		.start = -1,
+		.len = 25,
+		.names = NULL,
+	},
+
+	.num_controls = 5,
+	.controls = {
+		{ .num = 0, .type = SCARLETT_OUTPUTS, .name = "Monitor" },
+		{ .num = 1, .type = SCARLETT_OUTPUTS, .name = "Headphone" },
+		{ .num = 2, .type = SCARLETT_OUTPUTS, .name = "SPDIF" },
+		{ .num = 1, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+	},
+
+	.matrix_mux_init = {
+		 6,  7,  8,  9, 10, 11, 12, 13, /* Analog -> 1..8 */
+		16, 17, 18, 19, 20, 21,     /* ADAT[1..6] -> 9..14 */
+		14, 15,                          /* SPDIF -> 15,16 */
+		0, 1                          /* PCM[1,2] -> 17,18 */
+	}
+};
+
+static struct scarlett_device_info s18i8_info = {
+	.matrix_in = 18,
+	.matrix_out = 8,
+	.input_len = 18,
+	.output_len = 8,
+
+	.pcm_start = 0,
+	.analog_start = 8,
+	.spdif_start = 16,
+	.adat_start = 18,
+	.mix_start = 26,
+
+	.opt_master = {
+		.start = -1,
+		.len = 35,
+		.names = NULL
+	},
+
+	.opt_matrix = {
+		.start = -1,
+		.len = 27,
+		.names = NULL
+	},
+
+	.num_controls = 10,
+	.controls = {
+		{ .num = 0, .type = SCARLETT_OUTPUTS, .name = "Monitor" },
+		{ .num = 1, .type = SCARLETT_OUTPUTS, .name = "Headphone 1" },
+		{ .num = 2, .type = SCARLETT_OUTPUTS, .name = "Headphone 2" },
+		{ .num = 3, .type = SCARLETT_OUTPUTS, .name = "SPDIF" },
+		{ .num = 1, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 1, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 3, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 4, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+	},
+
+	.matrix_mux_init = {
+		 8,  9, 10, 11, 12, 13, 14, 15, /* Analog -> 1..8 */
+		18, 19, 20, 21, 22, 23,     /* ADAT[1..6] -> 9..14 */
+		16, 17,                          /* SPDIF -> 15,16 */
+		0, 1                          /* PCM[1,2] -> 17,18 */
+	}
+};
+
+static struct scarlett_device_info s18i20_info = {
+	.matrix_in = 18,
+	.matrix_out = 8,
+	.input_len = 18,
+	.output_len = 20,
+
+	.pcm_start = 0,
+	.analog_start = 20,
+	.spdif_start = 28,
+	.adat_start = 30,
+	.mix_start = 38,
+
+	.opt_master = {
+		.start = -1,
+		.len = 47,
+		.names = NULL
+	},
+
+	.opt_matrix = {
+		.start = -1,
+		.len = 39,
+		.names = NULL
+	},
+
+	.num_controls = 10,
+	.controls = {
+		{ .num = 0, .type = SCARLETT_OUTPUTS, .name = "Monitor" },
+		{ .num = 1, .type = SCARLETT_OUTPUTS, .name = "Line 3/4" },
+		{ .num = 2, .type = SCARLETT_OUTPUTS, .name = "Line 5/6" },
+		{ .num = 3, .type = SCARLETT_OUTPUTS, .name = "Line 7/8" },
+		{ .num = 4, .type = SCARLETT_OUTPUTS, .name = "Line 9/10" },
+		{ .num = 5, .type = SCARLETT_OUTPUTS, .name = "SPDIF" },
+		{ .num = 6, .type = SCARLETT_OUTPUTS, .name = "ADAT 1/2" },
+		{ .num = 7, .type = SCARLETT_OUTPUTS, .name = "ADAT 3/4" },
+		{ .num = 8, .type = SCARLETT_OUTPUTS, .name = "ADAT 5/6" },
+		{ .num = 9, .type = SCARLETT_OUTPUTS, .name = "ADAT 7/8" },
+		/*{ .num = 1, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 1, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_IMPEDANCE, .name = NULL},
+		{ .num = 2, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 3, .type = SCARLETT_SWITCH_PAD, .name = NULL},
+		{ .num = 4, .type = SCARLETT_SWITCH_PAD, .name = NULL},*/
+	},
+
+	.matrix_mux_init = {
+		20, 21, 22, 23, 24, 25, 26, 27, /* Analog -> 1..8 */
+		30, 31, 32, 33, 34, 35,     /* ADAT[1..6] -> 9..14 */
+		28, 29,                          /* SPDIF -> 15,16 */
+		0, 1                          /* PCM[1,2] -> 17,18 */
+	}
+};
+
+
+static int scarlett_controls_create_generic(struct usb_mixer_interface *mixer,
+	struct scarlett_device_info *info)
+{
+	int i = 0;
+	int err = 0;
+	char mx[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+	const struct scarlett_mixer_control *ctl;
+	struct usb_mixer_elem_info *elem;
+
+	/* create master switch and playback volume */
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_switch, 0x0a, 0x01, 0,
+			  USB_MIXER_S16, 1, "Master Playback Switch", NULL,
+			  &elem);
+	if (err < 0)
+		return err;
+
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_master, 0x0a, 0x02, 0,
+			  USB_MIXER_S16, 1, "Master Playback Volume", NULL,
+			  &elem);
+	if (err < 0)
+		return err;
+
+	/* iterate through controls in info struct and create each one */
+	for (i = 0; i < info->num_controls; i++) {
+		ctl = &info->controls[i];
+
+		switch (ctl->type) {
+		case SCARLETT_OUTPUTS:
+			err = add_output_ctls(mixer, ctl->num, ctl->name, info);
+			if (err < 0)
+				return err;
+			break;
+		case SCARLETT_SWITCH_IMPEDANCE:
+			sprintf(mx, "Input %d Impedance Switch",
+				ctl->num);
+			err = add_new_ctl(mixer, &usb_scarlett_ctl_enum, 0x01,
+					  0x09, ctl->num, USB_MIXER_S16, 1, mx,
+					  &opt_impedance, &elem);
+			if (err < 0)
+				return err;
+			break;
+		case SCARLETT_SWITCH_PAD:
+			sprintf(mx, "Input %d Pad Switch", ctl->num);
+			err = add_new_ctl(mixer, &usb_scarlett_ctl_enum, 0x01,
+					  0x0b, ctl->num, USB_MIXER_S16, 1, mx,
+					  &opt_pad, &elem);
+			if (err < 0)
+				return err;
+			break;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Create enumeration strings from device_info
+ */
+int scarlett_create_strings_from_info(struct scarlett_device_info *info)
+{
+	int i = 0, j = 0;
+	char **names;
+
+	names = kmalloc_array(info->opt_master.len, sizeof(char *), GFP_KERNEL);
+	if (!names) {
+		kfree(names);
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < info->opt_master.len; i++) {
+		names[i] = kmalloc_array(SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
+				   sizeof(char), GFP_KERNEL);
+		if (!names[i]) {
+			for (j = 0; j < i-1; j++)
+				kfree(names[j]);
+			kfree(names);
+			return -ENOMEM;
+		}
+		if (i > info->mix_start) {
+			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
+				 "Mix %c", 'A'+(i - info->mix_start - 1));
+		} else if (i > info->adat_start) {
+			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
+				 "ADAT %d", i - info->adat_start);
+		} else if (i > info->spdif_start) {
+			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
+				 "SPDIF %d", i - info->spdif_start);
+		} else if (i > info->analog_start) {
+			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
+				 "Analog %d", i - info->analog_start);
+		} else if (i > info->pcm_start) {
+			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
+				 "PCM %d", i - info->pcm_start);
+		} else {
+			snprintf(names[i], SNDRV_CTL_ELEM_ID_NAME_MAXLEN,
+				 "Off");
+		}
+	}
+
+	/* assign to the appropriate control */
+	info->opt_master.names = (const char * const *)names;
+	info->opt_matrix.names = (const char * const *)names;
+
+	return 0;
+}
+
+/*
+ * Create and initialize a mixer for the Focusrite(R) Scarlett
+ */
+int snd_scarlett_controls_create(struct usb_mixer_interface *mixer)
+{
+	int err, i, o;
+	char mx[SNDRV_CTL_ELEM_ID_NAME_MAXLEN];
+	struct scarlett_device_info *info;
+	struct usb_mixer_elem_info *elem;
+	static char sample_rate_buffer[4] = { '\x80', '\xbb', '\x00', '\x00' };
+
+	/* only use UAC_VERSION_2 */
+	if (!mixer->protocol)
+		return 0;
+
+	switch (mixer->chip->usb_id) {
+	case USB_ID(0x1235, 0x8012):
+		info = &s6i6_info;
+		break;
+	case USB_ID(0x1235, 0x8002):
+		info = &s8i6_info;
+		break;
+	case USB_ID(0x1235, 0x8004):
+		info = &s18i6_info;
+		break;
+	case USB_ID(0x1235, 0x8014):
+		info = &s18i8_info;
+		break;
+	case USB_ID(0x1235, 0x800c):
+		info = &s18i20_info;
+		break;
+	default: /* device not (yet) supported */
+		return -EINVAL;
+	}
+
+	/* generate strings dynamically for each control */
+	err = scarlett_create_strings_from_info(info);
+	if (err < 0)
+		return err;
+
+	/* generic function to create controls */
+	err = scarlett_controls_create_generic(mixer, info);
+	if (err < 0)
+		return err;
+
+	/* setup matrix controls */
+	for (i = 0; i < info->matrix_in; i++) {
+		snprintf(mx, sizeof(mx), "Matrix %02d Input Playback Route",
+			 i+1);
+		err = add_new_ctl(mixer, &usb_scarlett_ctl_enum, 0x32, 0x06, i,
+				  USB_MIXER_S16, 1, mx, &info->opt_matrix,
+				  &elem);
+		if (err < 0)
+			return err;
+
+		for (o = 0; o < info->matrix_out; o++) {
+			sprintf(mx, "Matrix %02d Mix %c Playback Volume", i+1,
+				o+'A');
+			err = add_new_ctl(mixer, &usb_scarlett_ctl, 0x3c, 0x00,
+					  (i << 3) + (o & 0x07), USB_MIXER_S16,
+					  1, mx, NULL, &elem);
+			if (err < 0)
+				return err;
+
+		}
+	}
+
+	for (i = 0; i < info->input_len; i++) {
+		snprintf(mx, sizeof(mx), "Input Source %02d Capture Route",
+			 i+1);
+		err = add_new_ctl(mixer, &usb_scarlett_ctl_enum, 0x34, 0x00, i,
+				  USB_MIXER_S16, 1, mx, &info->opt_master,
+				  &elem);
+		if (err < 0)
+			return err;
+	}
+
+	/* val_len == 1 needed here */
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_enum, 0x28, 0x01, 0,
+			  USB_MIXER_U8, 1, "Sample Clock Source",
+			  &opt_clock, &elem);
+	if (err < 0)
+		return err;
+
+	/* val_len == 1 and UAC2_CS_MEM */
+	err = add_new_ctl(mixer, &usb_scarlett_ctl_sync, 0x3c, 0x00, 2,
+			  USB_MIXER_U8, 1, "Sample Clock Sync Status",
+			  &opt_sync, &elem);
+	if (err < 0)
+		return err;
+
+	/* initialize sampling rate to 48000 */
+	err = snd_usb_ctl_msg(mixer->chip->dev,
+		usb_sndctrlpipe(mixer->chip->dev, 0), UAC2_CS_CUR,
+		USB_RECIP_INTERFACE | USB_TYPE_CLASS |
+		USB_DIR_OUT, 0x0100, snd_usb_ctrl_intf(mixer->chip) |
+		(0x29 << 8), sample_rate_buffer, 4);
+	if (err < 0)
+		return err;
+
+	return err;
+}
diff --git a/sound/usb/mixer_scarlett.h b/sound/usb/mixer_scarlett.h
new file mode 100644
index 0000000..19c592a
--- /dev/null
+++ b/sound/usb/mixer_scarlett.h
@@ -0,0 +1,6 @@ 
+#ifndef __USB_MIXER_SCARLETT_H
+#define __USB_MIXER_SCARLETT_H
+
+int snd_scarlett_controls_create(struct usb_mixer_interface *mixer);
+
+#endif /* __USB_MIXER_SCARLETT_H */