// SPDX-License-Identifier: GPL-2.0
/*
 * Presonus Studio 1810c driver for ALSA
 * Copyright (C) 2019 Nick Kossifidis <mickflemm@gmail.com>
 *
 * Based on reverse engineering of the communication protocol
 * between the windows driver / Univeral Control (UC) program
 * and the device, through usbmon.
 *
 * For now this bypasses the mixer, with all channels split,
 * so that the software can mix with greater flexibility.
 * It also adds controls for the 4 buttons on the front of
 * the device.
 */

#include <linux/usb.h>
#include <linux/usb/audio-v2.h>
#include <linux/slab.h>
#include <sound/core.h>
#include <sound/control.h>

#include "usbaudio.h"
#include "mixer.h"
#include "mixer_quirks.h"
#include "helper.h"
#include "mixer_s1810c.h"

/*
 * DISCLAIMER: These are just guesses based on the
 * dumps I got.
 *
 * It seems like a selects between
 * device (0), mixer (0x64) and output (0x65)
 *
 * For mixer (0x64):
 *  * b selects an input channel (see below).
 *  * c selects an output channel pair (see below).
 *  * d selects left (0) or right (1) of that pair.
 *  * e level : see MIXER_LEVEL_* defines below.
 *      Also used for setting volume levels
 *      in which case b is also set so I guess
 *      this way it is possible to set the volume
 *      level from the specified input to the
 *      specified output.
 *
 * IN Channels:
 * 0  - 7  Mic/Inst/Line (Analog inputs)
 * 8  - 9  S/PDIF
 * 10 - 17 ADAT
 * 18 - 35 DAW (Inputs from the host)
 *
 * OUT Channels (pairs):
 * 0 -> Main out
 * 1 -> Line1/2
 * 2 -> Line3/4
 * 3 -> S/PDIF
 * 4 -> ADAT?
 *
 * For device (0):
 *  * b and c are not used, at least not on the
 *    dumps I got.
 *  * d sets the control id to be modified
 *    (see below).
 *  * e sets the setting for that control.
 *    (so for the switches I was interested
 *    in it's 0/1)
 *
 * For output (0x65):
 *   * b is the output channel (see above).
 *   * c is zero.
 *   * e I guess the same as with mixer
 *
 */
/* struct s1810c_ctl_packet - basic vendor request
 * @selector: device/mixer/output
 * @b: request-dependant field b
 * @tag: fixed value identifying type of request
 * @len: sizeof this struct - 8 (excludes first 2 fields)
 *      i.e. for basic struct s1810c_ctl_packet: len is 5*4=0x14
 * @c: request-dependant field c
 * @d: request-dependant field d
 * @e: request-dependant field e
 *
 * See longer description above. This could be combined
 * (as a union?) with the longer struct s1810c_state_packet
 */
struct s1810c_ctl_packet {
        __le32 selector;
        __le32 b;
        __le32 tag;
        __le32 len;
        __le32 c;
        __le32 d;
        __le32 e;
};

/* selectors for CMD request
 */
#define SC1810C_SEL_DEVICE 0
#define SC1810C_SEL_MIXER 0x64
#define SC1810C_SEL_OUTPUT 0x65


/* control ids */
#define SC1810C_CTL_LINE_SW     0
#define SC1810C_CTL_MUTE_SW     1
#define SC1824C_CTL_MONO_SW     2
#define SC1810C_CTL_AB_SW       3
#define SC1810C_CTL_48V_SW      4

/* USB Control (vendor) requests
 */
#define SC1810C_CMD_REQ 160
#define SC1810C_CMD_REQTYPE \
        (USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_OUT)
#define SC1810C_CMD_TAG         0x50617269
#define SC1810C_CMD_LEN         0x14

#define SC1810C_SET_STATE_REQ   161
#define SC1810C_SET_STATE_REQTYPE SC1810C_CMD_REQTYPE
#define SC1810C_SET_STATE_TAG   0x64656D73
#define SC1810C_SET_STATE_LEN   0xF4

#define SC1810C_GET_STATE_REQ   162
#define SC1810C_GET_STATE_REQTYPE \
        (USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN)
#define SC1810C_GET_STATE_TAG   SC1810C_SET_STATE_TAG
#define SC1810C_GET_STATE_LEN   SC1810C_SET_STATE_LEN

/* Mixer levels normally range from 0 (off) to 0x0100 0000 (0 dB).
 * raw_level = 2^24 * 10^(db_level / 20), thus
 * -3dB = 0xb53bf0 (technically, half-power -3.01...dB would be 0xb504f3)
 * -96dB = 0x109
 * -99dB = 0xBC
 * PC software sliders cover -96 to +10dB (0x0329 8b08),
 * but the value 0 (-inf dB) can be used when e.g. Mixer Bypass is enabled.
 * Unclear what the hardware's maximum value is.
 *
 * Note, when a channel is panned to two channels (stereo),
 * the mixer level is set to slider value (by default -96dB) minus 3dB,
 * which explains the -99dB value seen in USB captures.
 */
#define MIXER_LEVEL_MUTE 0
#define MIXER_LEVEL_N99DB 0xbc
#define MIXER_LEVEL_N3DB 0xb53bf0
#define MIXER_LEVEL_0DB 0x1000000

/*
 * This packet includes mixer volumes and
 * various other fields, it's an extended
 * version of ctl_packet, with a and b
 * being zero and different tag/length.
 */
struct s1810c_state_packet {
        __le32 fields[63];
};

/* indices into s1810c_state_packet.fields[]
 */
#define SC1810C_STATE_TAG_IDX   2
#define SC1810C_STATE_LEN_IDX   3

#define SC1810C_STATE_48V_SW    58
#define SC1810C_STATE_LINE_SW   59
#define SC1810C_STATE_MUTE_SW   60
#define SC1824C_STATE_MONO_SW   61
#define SC1810C_STATE_AB_SW     62

struct s1810_mixer_state {
        uint16_t seqnum;
        struct mutex usb_mutex;
        struct mutex data_mutex;
};

static int
snd_s1810c_send_ctl_packet(struct usb_device *dev, u32 sel,
                           u32 b, u32 c, u32 d, u32 e)
{
        struct s1810c_ctl_packet pkt = { 0 };
        int ret = 0;

        pkt.tag = __cpu_to_le32(SC1810C_CMD_TAG);
        pkt.len = __cpu_to_le32(SC1810C_CMD_LEN);

        pkt.selector = __cpu_to_le32(sel);
        pkt.b = __cpu_to_le32(b);
        pkt.c = __cpu_to_le32(c);
        pkt.d = __cpu_to_le32(d);
        pkt.e = __cpu_to_le32(e);

        ret = snd_usb_ctl_msg(dev, usb_sndctrlpipe(dev, 0),
                              SC1810C_CMD_REQ,
                              SC1810C_CMD_REQTYPE, 0, 0, &pkt, sizeof(pkt));
        if (ret < 0) {
                dev_warn(&dev->dev, "could not send ctl packet\n");
                return ret;
        }
        return 0;
}

/*
 * When opening Universal Control the program periodically
 * sends and receives state packets for syncinc state between
 * the device and the host.
 *
 * Note that if we send only the request to get data back we'll
 * get an error, we need to first send an empty state packet and
 * then ask to receive a filled. Their seqnumbers must also match.
 */
static int
snd_sc1810c_get_status_field(struct usb_device *dev,
                             u32 *field, int field_idx, uint16_t *seqnum)
{
        struct s1810c_state_packet pkt_out = { { 0 } };
        struct s1810c_state_packet pkt_in = { { 0 } };
        int ret = 0;

        pkt_out.fields[SC1810C_STATE_TAG_IDX] = __cpu_to_le32(SC1810C_SET_STATE_TAG);
        pkt_out.fields[SC1810C_STATE_LEN_IDX] = __cpu_to_le32(SC1810C_SET_STATE_LEN);
        ret = snd_usb_ctl_msg(dev, usb_sndctrlpipe(dev, 0),
                              SC1810C_SET_STATE_REQ,
                              SC1810C_SET_STATE_REQTYPE,
                              (*seqnum), 0, &pkt_out, sizeof(pkt_out));
        if (ret < 0) {
                dev_warn(&dev->dev, "could not send state packet (%d)\n", ret);
                return ret;
        }

        ret = snd_usb_ctl_msg(dev, usb_rcvctrlpipe(dev, 0),
                              SC1810C_GET_STATE_REQ,
                              SC1810C_GET_STATE_REQTYPE,
                              (*seqnum), 0, &pkt_in, sizeof(pkt_in));
        if (ret < 0) {
                dev_warn(&dev->dev, "could not get state field %u (%d)\n",
                         field_idx, ret);
                return ret;
        }

        (*field) = __le32_to_cpu(pkt_in.fields[field_idx]);
        (*seqnum)++;
        return 0;
}

/*
 * This is what I got when bypassing the mixer with
 * all channels split. I'm not 100% sure of what's going
 * on, I could probably clean this up based on my observations
 * but I prefer to keep the same behavior as the windows driver.
 */
static int snd_s1810c_init_mixer_maps(struct snd_usb_audio *chip)
{
        u32 a, b, c, e, n, off, left, right;
        struct usb_device *dev = chip->dev;

        switch (chip->usb_id) {
        case USB_ID(0x194f, 0x010c): /* 1810c */
                /* Set initial volume levels ? */
                a = SC1810C_SEL_MIXER;
                e = MIXER_LEVEL_N99DB;
                for (n = 0; n < 2; n++) {
                        off = n * 18;
                        for (b = off; b < 18 + off; b++) {
                                /* This channel to all outputs ? */
                                for (c = 0; c <= 8; c++) {
                                        snd_s1810c_send_ctl_packet(dev, a, b, c, 0, e);
                                        snd_s1810c_send_ctl_packet(dev, a, b, c, 1, e);
                                }
                                /* This channel to main output (again) */
                                snd_s1810c_send_ctl_packet(dev, a, b, 0, 0, e);
                                snd_s1810c_send_ctl_packet(dev, a, b, 0, 1, e);
                        }
                        /*
                         * I noticed on UC that DAW channels have different
                         * initial volumes, so this makes sense.
                         */
                        e = MIXER_LEVEL_N3DB;
                }

                /* Connect analog outputs ? */
                a = SC1810C_SEL_OUTPUT;
                for (b = 1; b < 3; b++) {
                        snd_s1810c_send_ctl_packet(dev, a, b, 0, 0, MIXER_LEVEL_0DB);
                        snd_s1810c_send_ctl_packet(dev, a, b, 0, 1, MIXER_LEVEL_0DB);
                }
                snd_s1810c_send_ctl_packet(dev, a, 0, 0, 0, MIXER_LEVEL_0DB);
                snd_s1810c_send_ctl_packet(dev, a, 0, 0, 1, MIXER_LEVEL_0DB);

                /* Set initial volume levels for S/PDIF mappings ? */
                a = SC1810C_SEL_MIXER;
                e = MIXER_LEVEL_N99DB;
                c = 3;
                for (n = 0; n < 2; n++) {
                        off = n * 18;
                        for (b = off; b < 18 + off; b++) {
                                snd_s1810c_send_ctl_packet(dev, a, b, c, 0, e);
                                snd_s1810c_send_ctl_packet(dev, a, b, c, 1, e);
                        }
                        e = MIXER_LEVEL_N3DB;
                }

                /* Connect S/PDIF output ? */
                a = SC1810C_SEL_OUTPUT;
                snd_s1810c_send_ctl_packet(dev, a, 3, 0, 0, MIXER_LEVEL_0DB);
                snd_s1810c_send_ctl_packet(dev, a, 3, 0, 1, MIXER_LEVEL_0DB);

                /* Connect all outputs (again) ? */
                a = SC1810C_SEL_OUTPUT;
                for (b = 0; b < 4; b++) {
                        snd_s1810c_send_ctl_packet(dev, a, b, 0, 0, MIXER_LEVEL_0DB);
                        snd_s1810c_send_ctl_packet(dev, a, b, 0, 1, MIXER_LEVEL_0DB);
                }

                /* Basic routing to get sound out of the device */
                a = SC1810C_SEL_MIXER;
                for (c = 0; c < 4; c++) {
                        for (b = 0; b < 36; b++) {
                                if ((c == 0 && b == 18) ||      /* DAW1/2 -> Main */
                                        (c == 1 && b == 20) ||  /* DAW3/4 -> Line3/4 */
                                        (c == 2 && b == 22) ||  /* DAW4/5 -> Line5/6 */
                                        (c == 3 && b == 24)) {  /* DAW5/6 -> S/PDIF */
                                        /* Left */
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 0, MIXER_LEVEL_0DB);
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 1, MIXER_LEVEL_MUTE);
                                        b++;
                                        /* Right */
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 0, MIXER_LEVEL_MUTE);
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 1, MIXER_LEVEL_0DB);
                                } else {
                                        /* Leave the rest disconnected */
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 0, MIXER_LEVEL_MUTE);
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 1, MIXER_LEVEL_MUTE);
                                }
                        }
                }

                /* Set initial volume levels for S/PDIF (again) ? */
                a = SC1810C_SEL_MIXER;
                e = MIXER_LEVEL_N99DB;
                c = 3;
                for (n = 0; n < 2; n++) {
                        off = n * 18;
                        for (b = off; b < 18 + off; b++) {
                                snd_s1810c_send_ctl_packet(dev, a, b, c, 0, e);
                                snd_s1810c_send_ctl_packet(dev, a, b, c, 1, e);
                        }
                        e = MIXER_LEVEL_N3DB;
                }

                /* Connect S/PDIF outputs (again) ? */
                a = SC1810C_SEL_OUTPUT;
                snd_s1810c_send_ctl_packet(dev, a, 3, 0, 0, MIXER_LEVEL_0DB);
                snd_s1810c_send_ctl_packet(dev, a, 3, 0, 1, MIXER_LEVEL_0DB);

                /* Again ? */
                snd_s1810c_send_ctl_packet(dev, a, 3, 0, 0, MIXER_LEVEL_0DB);
                snd_s1810c_send_ctl_packet(dev, a, 3, 0, 1, MIXER_LEVEL_0DB);
                break;

        case USB_ID(0x194f, 0x010d): /* 1824c */
                /* Set all output faders to unity gain */
                a = SC1810C_SEL_OUTPUT;
                c = 0x00;
                for (b = 0; b < 9; b++) {
                        snd_s1810c_send_ctl_packet(dev, a, b, c, 0, MIXER_LEVEL_0DB);
                        snd_s1810c_send_ctl_packet(dev, a, b, c, 1, MIXER_LEVEL_0DB);
                }

                /* Set
                 * Daw 1 -> Line out 1 (left), Daw 2 -> Line out 2 (right)
                 * Daw 3 -> Line out 3, (left) Daw 4 -> Line out 4 (right)
                 * Daw 5 -> Line out 5, (left) Daw 6 -> Line out 6 (right)
                 * Daw 7 -> Line out 7, (left) Daw 8 -> Line out 8 (right)
                 * Daw 9 -> SPDIF out 1, (left) Daw 10 -> SPDIF out 2 (right)
                 * Daw 11 -> ADAT out 1, (left) Daw 12 -> ADAT out 2 (right)
                 * Daw 13 -> ADAT out 3, (left) Daw 14 -> ADAT out 4 (right)
                 * Daw 15 -> ADAT out 5, (left) Daw 16 -> ADAT out 6 (right)
                 * Daw 17 -> ADAT out 7, (left) Daw 18 -> ADAT out 8 (right)
                 * Everything else muted
                 */
                a = SC1810C_SEL_MIXER;
                /* The first Daw channel is channel 18 */
                left = 18;

                for (c = 0; c < 9; c++) {
                        right = left + 1;

                        for (b = 0; b < 36; b++) {
                                if (b == left) {
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 0, MIXER_LEVEL_0DB);
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 1, MIXER_LEVEL_MUTE);
                                } else if (b == right) {
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 0, MIXER_LEVEL_MUTE);
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 1, MIXER_LEVEL_0DB);
                                } else {
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 0, MIXER_LEVEL_MUTE);
                                        snd_s1810c_send_ctl_packet(dev,
                                                        a, b, c, 1, MIXER_LEVEL_MUTE);
                                }
                        }
                        left += 2;
                }
                break;
        }
        return 0;
}

/*
 * Sync state with the device and retrieve the requested field,
 * whose index is specified in (kctl->private_value & 0xFF),
 * from the received fields array.
 */
static int
snd_s1810c_get_switch_state(struct usb_mixer_interface *mixer,
                            struct snd_kcontrol *kctl, u32 *state)
{
        struct snd_usb_audio *chip = mixer->chip;
        struct s1810_mixer_state *private = mixer->private_data;
        u32 field = 0;
        u32 ctl_idx = (u32) (kctl->private_value & 0xFF);
        int ret;

        guard(mutex)(&private->usb_mutex);
        ret = snd_sc1810c_get_status_field(chip->dev, &field,
                                           ctl_idx, &private->seqnum);
        if (ret < 0)
                return ret;

        *state = field;
        return ret;
}

/*
 * Send a control packet to the device for the control id
 * specified in (kctl->private_value >> 8) with value
 * specified in (kctl->private_value >> 16).
 */
static int
snd_s1810c_set_switch_state(struct usb_mixer_interface *mixer,
                            struct snd_kcontrol *kctl)
{
        struct snd_usb_audio *chip = mixer->chip;
        struct s1810_mixer_state *private = mixer->private_data;
        u32 pval = (u32) kctl->private_value;
        u32 ctl_id = (pval >> 8) & 0xFF;
        u32 ctl_val = (pval >> 16) & 0x1;

        guard(mutex)(&private->usb_mutex);
        return snd_s1810c_send_ctl_packet(chip->dev, 0, 0, 0, ctl_id, ctl_val);
}

/* Generic get/set/init functions for switch controls */

static int
snd_s1810c_switch_get(struct snd_kcontrol *kctl,
                      struct snd_ctl_elem_value *ctl_elem)
{
        struct usb_mixer_elem_list *list = snd_kcontrol_chip(kctl);
        struct usb_mixer_interface *mixer = list->mixer;
        struct s1810_mixer_state *private = mixer->private_data;
        u32 pval = (u32) kctl->private_value;
        u32 ctl_idx = pval & 0xFF;
        u32 state = 0;
        int ret;

        guard(mutex)(&private->data_mutex);
        ret = snd_s1810c_get_switch_state(mixer, kctl, &state);
        if (ret < 0)
                return ret;

        switch (ctl_idx) {
        case SC1810C_STATE_LINE_SW:
        case SC1810C_STATE_AB_SW:
                ctl_elem->value.enumerated.item[0] = (int)state;
                break;
        default:
                ctl_elem->value.integer.value[0] = (long)state;
        }

        return 0;
}

static int
snd_s1810c_switch_set(struct snd_kcontrol *kctl,
                      struct snd_ctl_elem_value *ctl_elem)
{
        struct usb_mixer_elem_list *list = snd_kcontrol_chip(kctl);
        struct usb_mixer_interface *mixer = list->mixer;
        struct s1810_mixer_state *private = mixer->private_data;
        u32 pval = (u32) kctl->private_value;
        u32 ctl_idx = pval & 0xFF;
        u32 curval = 0;
        u32 newval = 0;
        int ret = 0;

        guard(mutex)(&private->data_mutex);
        ret = snd_s1810c_get_switch_state(mixer, kctl, &curval);
        if (ret < 0)
                return ret;

        switch (ctl_idx) {
        case SC1810C_STATE_LINE_SW:
        case SC1810C_STATE_AB_SW:
                newval = (u32) ctl_elem->value.enumerated.item[0];
                break;
        default:
                newval = (u32) ctl_elem->value.integer.value[0];
        }

        if (curval == newval)
                return 0;

        kctl->private_value &= ~(0x1 << 16);
        kctl->private_value |= (unsigned int)(newval & 0x1) << 16;
        ret = snd_s1810c_set_switch_state(mixer, kctl);

        return (ret < 0) ? 0 : 1;
}

static int
snd_s1810c_switch_init(struct usb_mixer_interface *mixer,
                       const struct snd_kcontrol_new *new_kctl)
{
        struct snd_kcontrol *kctl;
        struct usb_mixer_elem_info *elem;

        elem = kzalloc_obj(struct usb_mixer_elem_info);
        if (!elem)
                return -ENOMEM;

        elem->head.mixer = mixer;
        elem->control = 0;
        elem->head.id = 0;
        elem->channels = 1;

        kctl = snd_ctl_new1(new_kctl, elem);
        if (!kctl) {
                kfree(elem);
                return -ENOMEM;
        }
        kctl->private_free = snd_usb_mixer_elem_free;

        return snd_usb_mixer_add_control(&elem->head, kctl);
}

static int
snd_s1810c_line_sw_info(struct snd_kcontrol *kctl,
                        struct snd_ctl_elem_info *uinfo)
{
        static const char *const texts[2] = {
                "Preamp On (Mic/Inst)",
                "Preamp Off (Line in)"
        };

        return snd_ctl_enum_info(uinfo, 1, ARRAY_SIZE(texts), texts);
}

static const struct snd_kcontrol_new snd_s1810c_line_sw = {
        .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
        .name = "Line 1/2 Source Type",
        .info = snd_s1810c_line_sw_info,
        .get = snd_s1810c_switch_get,
        .put = snd_s1810c_switch_set,
        .private_value = (SC1810C_STATE_LINE_SW | SC1810C_CTL_LINE_SW << 8)
};

static const struct snd_kcontrol_new snd_s1810c_mute_sw = {
        .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
        .name = "Mute Main Out Switch",
        .info = snd_ctl_boolean_mono_info,
        .get = snd_s1810c_switch_get,
        .put = snd_s1810c_switch_set,
        .private_value = (SC1810C_STATE_MUTE_SW | SC1810C_CTL_MUTE_SW << 8)
};

static const struct snd_kcontrol_new snd_s1824c_mono_sw = {
        .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
        .name = "Mono Main Out Switch",
        .info = snd_ctl_boolean_mono_info,
        .get = snd_s1810c_switch_get,
        .put = snd_s1810c_switch_set,
        .private_value = (SC1824C_STATE_MONO_SW | SC1824C_CTL_MONO_SW << 8)
};

static const struct snd_kcontrol_new snd_s1810c_48v_sw = {
        .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
        .name = "48V Phantom Power On Mic Inputs Switch",
        .info = snd_ctl_boolean_mono_info,
        .get = snd_s1810c_switch_get,
        .put = snd_s1810c_switch_set,
        .private_value = (SC1810C_STATE_48V_SW | SC1810C_CTL_48V_SW << 8)
};

static int
snd_s1810c_ab_sw_info(struct snd_kcontrol *kctl,
                      struct snd_ctl_elem_info *uinfo)
{
        static const char *const texts[2] = {
                "1/2",
                "3/4"
        };

        return snd_ctl_enum_info(uinfo, 1, ARRAY_SIZE(texts), texts);
}

static const struct snd_kcontrol_new snd_s1810c_ab_sw = {
        .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
        .name = "Headphone 1 Source Route",
        .info = snd_s1810c_ab_sw_info,
        .get = snd_s1810c_switch_get,
        .put = snd_s1810c_switch_set,
        .private_value = (SC1810C_STATE_AB_SW | SC1810C_CTL_AB_SW << 8)
};

static void snd_sc1810_mixer_state_free(struct usb_mixer_interface *mixer)
{
        struct s1810_mixer_state *private = mixer->private_data;
        kfree(private);
        mixer->private_data = NULL;
}

/* Entry point, called from mixer_quirks.c */
int snd_sc1810_init_mixer(struct usb_mixer_interface *mixer)
{
        struct s1810_mixer_state *private = NULL;
        struct snd_usb_audio *chip = mixer->chip;
        struct usb_device *dev = chip->dev;
        int ret = 0;

        /* Run this only once */
        if (!list_empty(&chip->mixer_list))
                return 0;

        ret = snd_s1810c_init_mixer_maps(chip);
        if (ret < 0)
                return ret;

        private = kzalloc_obj(struct s1810_mixer_state);
        if (!private)
                return -ENOMEM;

        mutex_init(&private->usb_mutex);
        mutex_init(&private->data_mutex);

        mixer->private_data = private;
        mixer->private_free = snd_sc1810_mixer_state_free;

        private->seqnum = 1;

        ret = snd_s1810c_switch_init(mixer, &snd_s1810c_line_sw);
        if (ret < 0)
                return ret;

        ret = snd_s1810c_switch_init(mixer, &snd_s1810c_mute_sw);
        if (ret < 0)
                return ret;

        ret = snd_s1810c_switch_init(mixer, &snd_s1810c_48v_sw);
        if (ret < 0)
                return ret;

        switch (chip->usb_id) {
        case USB_ID(0x194f, 0x010c): /* Presonus Studio 1810c */
                dev_info(&dev->dev,
                         "Presonus Studio 1810c, device_setup: %u\n", chip->setup);
                if (chip->setup == 1)
                        dev_info(&dev->dev, "(8out/18in @ 48kHz)\n");
                else if (chip->setup == 2)
                        dev_info(&dev->dev, "(6out/8in @ 192kHz)\n");
                else
                        dev_info(&dev->dev, "(8out/14in @ 96kHz)\n");

                ret = snd_s1810c_switch_init(mixer, &snd_s1810c_ab_sw);
                if (ret < 0)
                        return ret;

                break;
        case USB_ID(0x194f, 0x010d): /* Presonus Studio 1824c */
                ret = snd_s1810c_switch_init(mixer, &snd_s1824c_mono_sw);
                if (ret < 0)
                        return ret;

                break;
        }

        return ret;
}