[RFC PATCH v5 2/8] ALSA: usb: babyfacepro: add output masters and crosspoint routing

[Ismaïl Bahloul]

Adds the first mixer controls: the six output masters (volume + mute)
and the 6x14 crosspoint routing matrix, plus the cold-init default
mixer that wires every source to every output at unity so the card
makes sound without any user-space mixer at all.

Masters and crosspoints ship together because the default-mixer setup
has to write both in one pass - output masters with no signal routed
to them would just be a silent volume knob.  This is the first patch
in the series where the card produces controllable, routed audio.

Also introduces mixer-state persistence across interface re-probes
(a userspace usbfs claim, e.g. PipeWire or the TuxMix daemon, detaches
and re-probes us) and across suspend/resume's cold re-init, trimmed
for now to the masters and crosspoints this patch adds; later patches
in the series extend babyface_restore_state()/struct bf_saved the same
way as they add more mixer state to cache.

bf_flag_cycle[]/bf_vendor_write_cycle()/bf_crosspoint_clear_cross(),
previously sketched in the core file, move to babyfacepro-ctl.c since
they are crosspoint/mixer-only.

Co-developed-by: David Fredman <davfre@xxxxxxxxx>
Signed-off-by: David Fredman <davfre@xxxxxxxxx>
Signed-off-by: Ismaïl Bahloul <i.bahloul01@xxxxxxxxx>
---
 sound/usb/babyfacepro/Makefile          |   2 +-
 sound/usb/babyfacepro/babyfacepro-ctl.c | 707 ++++++++++++++++++++++++
 sound/usb/babyfacepro/babyfacepro.c     | 189 ++++++-
 sound/usb/babyfacepro/babyfacepro.h     | 121 +++-
 4 files changed, 1013 insertions(+), 6 deletions(-)
 create mode 100644 sound/usb/babyfacepro/babyfacepro-ctl.c

diff --git a/sound/usb/babyfacepro/Makefile b/sound/usb/babyfacepro/Makefile
index 5adc6d474..a50647a06 100644
--- a/sound/usb/babyfacepro/Makefile
+++ b/sound/usb/babyfacepro/Makefile
@@ -1,4 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
-snd-usb-babyface-pro-y := babyfacepro.o
+snd-usb-babyface-pro-y := babyfacepro.o babyfacepro-ctl.o
 
 obj-$(CONFIG_SND_USB_BABYFACE_PRO) += snd-usb-babyface-pro.o
diff --git a/sound/usb/babyfacepro/babyfacepro-ctl.c b/sound/usb/babyfacepro/babyfacepro-ctl.c
new file mode 100644
index 000000000..a3d3252f5
--- /dev/null
+++ b/sound/usb/babyfacepro/babyfacepro-ctl.c
@@ -0,0 +1,707 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * RME Babyface Pro / Pro FS - proprietary-mode USB audio driver
+ *
+ * ALSA control surface: this patch adds the output masters (volume +
+ * mute) and the crosspoint routing matrix - the minimum needed for
+ * the card to produce controllable, routed audio.  They ship together
+ * because babyface_write_default_mixer() (the cold-init default
+ * mixer) has to set up both in one pass: masters with no signal
+ * routed to them would just be a silent volume knob.
+ *
+ * Preamp/gain, the routing-flag switches (loopback, AN1>2, link,
+ * clock source, width, FX send, DIM), varispeed pitch, the front
+ * panel and the DSP EQ are added by later patches in this series -
+ * see babyfacepro.h and the cover letter for the full plan.
+ *
+ * See babyfacepro.h for the shared device state and register map,
+ * and babyfacepro.c for the core driver (protocol, PCM streaming,
+ * state persistence, card lifecycle).
+ */
+#include <linux/log2.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/unaligned.h>
+#include <linux/usb.h>
+#include <linux/workqueue.h>
+#include <sound/control.h>
+#include <sound/tlv.h>
+#include <sound/core.h>
+#include <sound/initval.h>
+#include <sound/pcm.h>
+
+#include "babyfacepro.h"
+
+/* The flag-cycle counter, its writer and the per-block crosspoint
+ * "cross" register clear are crosspoint/mixer-only, so they live here
+ * rather than in the core driver file.
+ */
+
+/* The transaction-flag counter cycle on 16-bit writes. */
+const u16 bf_flag_cycle[4] = { 0xc000, 0x4000, 0x8000, 0x0000 };
+
+/* Write with the per-transaction flag-cycle word OR'd into idx.  The
+ * device wants the flag word (0xc000/0x4000/0x8000/0x0000, rotating)
+ * set on every 0x12/0x1a write; this is the hot path for the mixer
+ * puts, so it is factored out.
+ */
+int bf_vendor_write_cycle(struct snd_usb_babyface *chip, u8 req, u16 val, u16 idx)
+{
+	u16 flag = bf_flag_cycle[chip->flag_cnt];
+
+	chip->flag_cnt = (chip->flag_cnt + 1) & 3;
+	return bf_vendor_write(chip, req, val, idx | flag);
+}
+
+/* The 0x16 cold-init clear covers only 0x00-0x3D - the "cross"
+ * registers of a block (L-reg odd / R-reg even of the stereo
+ * sources) survive from the previous session and would sum L+R into
+ * BOTH channels of the output (mono).  Zero them explicitly: 10 odd
+ * L-registers (5,7,...23) + 10 even R-registers (4,6,...22).
+ */
+int bf_crosspoint_clear_cross(struct snd_usb_babyface *chip,
+			      unsigned int blk)
+{
+	int ret, k;
+
+	for (k = BF_CROSS_L_FIRST; k <= BF_CROSS_L_LAST; k += 2) {
+		ret = bf_vendor_write_cycle(chip, BF_REQ_CROSSPOINT, 0x0000,
+					    BF_REG_CROSS_BASE_L +
+					    BF_REG_CROSS_STRIDE * blk + k);
+		if (ret < 0)
+			return ret;
+	}
+	for (k = BF_CROSS_R_FIRST; k <= BF_CROSS_R_LAST; k += 2) {
+		ret = bf_vendor_write_cycle(chip, BF_REQ_CROSSPOINT, 0x0000,
+					    BF_REG_CROSS_BASE_R +
+					    BF_REG_CROSS_STRIDE * blk + k);
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
+const struct bf_source bf_sources[14] = {
+	{ "AN1",     0,  0 },
+	{ "AN2",     1,  1 },
+	{ "AN3",     2,  2 },
+	{ "AN4",     3,  3 },
+	{ "AS1/2",   4,  5 },
+	{ "ADAT3/4", 6,  7 },
+	{ "ADAT5/6", 8,  9 },
+	{ "ADAT7/8", 10, 11 },
+	{ "PB1",    12, 13 },
+	{ "PB2",    14, 15 },
+	{ "PB3",    16, 17 },
+	{ "PB4",    18, 19 },
+	{ "PB5",    20, 21 },
+	{ "PB6",    22, 23 },
+};
+
+/* Crosspoint-map output order vs the master-map order - HARDWARE-
+ * VERIFIED 2026-08-24: the block that feeds the Phones is the FIRST
+ * crosspoint block (0x34), while the Phones master is the SECOND
+ * (0x03E2/0x0006).  The crosspoint map lists the Phones first (the
+ * monitor output); the master map lists AN1/2 first.  Control index =
+ * the canonical order (AN1/2=0, PH3/4=1, ...) so the crosspoint and
+ * master controls line up; this table maps to the register block.
+ */
+const u8 bf_xpoint_block[6] = { 1, 0, 2, 3, 4, 5 };
+
+/* Master-register output order - the master map lists AN1/2 first
+ * (0x03E0) and the Phones master SECOND (0x03E2, HARDWARE-VERIFIED
+ * 2026-08-24); the crosspoint blocks are in the opposite order
+ * (Phones = block 0x34 first, hence bf_xpoint_block above).  Control
+ * index -> canonical output (AN1/2=0, PH3/4=1, ...) = the master
+ * register position directly: the names 'AN1/2 Playback Volume' etc.
+ * must match the register they write (corrected 2026-08-26 - the
+ * previous {1,0,...} swap made 'AN1/2' drive the Phones and 'PH3/4'
+ * drive the AN1/2 analog out).
+ */
+static const u8 bf_master_out[6] = { 0, 1, 2, 3, 4, 5 };
+
+/* The 16-bit master value -> the 8-bit companion code (0.5 dB/step).
+ * Integer-only: half_db = 12*log2(v/0x2000) via ilog2 + an 8-bit
+ * fractional-octave table (12*log2(1 + n/256), ~0.05 dB resolution -
+ * fine enough for the +/-0.5 dB panel wheel to track the round-trip).
+ */
+static const u8 bf_lg2_frac[256] = {
+	0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1,
+	1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2,
+	2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
+	3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4,
+	4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 5, 5, 5, 5,
+	5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
+	6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
+	6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
+	7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8,
+	8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
+	8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9,
+	9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 10, 10, 10, 10,
+	10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
+	10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
+	11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
+	11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
+};
+
+/* 16-bit master -> dBx2 (12 half-dB per octave; 0x2000 = 0 dB).
+ * Shared by the 8-bit companion and the front-panel OUT wheel.
+ */
+int bf_master_half_db(u16 vol16)
+{
+	unsigned int k, frac;
+
+	vol16 = clamp(vol16, 1, 0x4000);
+	k = ilog2(vol16);
+	frac = ((vol16 - (1u << k)) << 8) >> k;
+	return 12 * (int)k - 156 + bf_lg2_frac[frac];
+}
+
+/* dBx2 -> 16-bit master (0x2000*2^(half_db/12), rounded).  The
+ * inverse of bf_master_half_db - the 12th-root table 2^(n/12).
+ */
+static const u16 bf_twelfth[12] = {
+	0x1000, 0x10f4, 0x11f6, 0x1307, 0x1429, 0x155c,
+	0x16a1, 0x17f9, 0x1966, 0x1ae9, 0x1c82, 0x1e34,
+};
+
+int bf_master_16bit(int half_db)
+{
+	int k = half_db / 12;
+	int n = half_db % 12;
+	u32 v;
+
+	if (n < 0) {
+		n += 12;
+		k--;
+	}
+	v = (u32)bf_twelfth[n] << 1;	/* 0x2000*2^(n/12) */
+	if (k >= 0) {
+		v <<= k;
+	} else {
+		v += 1u << (-k - 1);	/* round-half-up */
+		v >>= -k;
+	}
+	return (u16)clamp(v, 1, 0x4000);
+}
+
+u8 bf_master_8bit(u16 vol16)
+{
+	if (vol16 == 0)
+		return BF_MASTER_MUTE;
+	return (u8)clamp(0xf3 + bf_master_half_db(vol16), BF_MASTER_8_MIN, 0xff);
+}
+
+/* The cold-init register clear zeroes the mixer registers TotalMix
+ * re-uploads afterwards.  The kernel driver has no saved scene (no
+ * readback for faders), so it applies TotalMix's factory routing -
+ * every source to every output at unity - so the card makes sound
+ * without any user-space mixer at all.
+ *
+ * The two analog masters (AN1/2, the main out; PH3/4, the headphone
+ * out) come up at -20 dB rather than TotalMix's 0 dB.  Routing all 14
+ * sources into an output at unity means they SUM, and this runs on
+ * every fresh load, before alsa-restore has had a chance to put the
+ * user's own levels back.  On monitors or headphones with no volume
+ * control of their own that is a real hazard, and the failure is
+ * asymmetric: a default that is too quiet is turned up in a second,
+ * one that is too loud cannot be taken back.  -20 dB is still plainly
+ * audible, and it is not an invented number - it is the exact
+ * 8-bit/16-bit pair the hardware's own DIM button writes.
+ *
+ * The other four outputs (AS1/2, ADAT3/4, ADAT5/6, ADAT7/8) are all
+ * digital, carried over the single optical port - nothing downstream
+ * of them can be damaged by a loud signal the way a speaker or a pair
+ * of headphones can, so there is no hazard to mitigate, only a
+ * digital feed that would otherwise arrive 20 dB quiet for no reason
+ * a downstream device could infer.  They keep TotalMix's own 0 dB
+ * default (raised 2026-09-15 after David Fredman pointed out the
+ * blanket -20 dB reached them too, on his report of the AN1/2/PH3/4
+ * default - issue #4).
+ */
+int babyface_write_default_mixer(struct snd_usb_babyface *chip)
+{
+	int out, src, ret;
+	u16 flag;
+
+	/* Output masters: the two analog outputs at -20 dB, the four
+	 * digital ones at 0 dB (see the comment above).  Unmuted either
+	 * way.
+	 */
+	for (out = 0; out < 6; out++) {
+		bool analog = out < 2;
+		u8 gain8 = analog ? BF_MASTER_MINUS20_8 : BF_MASTER_UNMUTE;
+		u16 gain16 = analog ? BF_MASTER_MINUS20_16 : BF_MASTER_0DB;
+
+		ret = bf_vendor_write(chip, BF_REQ_GAIN, gain8,
+				      BF_REG_MASTER_8 + 2 * out);
+		if (ret < 0)
+			return ret;
+		ret = bf_vendor_write(chip, BF_REQ_GAIN, gain8,
+				      BF_REG_MASTER_8 + 2 * out + 1);
+		if (ret < 0)
+			return ret;
+		flag = bf_flag_cycle[chip->flag_cnt];
+		chip->flag_cnt = (chip->flag_cnt + 1) & 3;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, gain16,
+				      (BF_REG_MASTER_16 + 2 * out) | flag);
+		if (ret < 0)
+			return ret;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, gain16,
+				      (BF_REG_MASTER_16 + 2 * out + 1) | flag);
+		if (ret < 0)
+			return ret;
+		chip->master[out][0] = gain16;
+		chip->master[out][1] = gain16;
+		chip->muted[out] = false;
+	}
+
+	/* Every source into every output pair, L and R, at 0 dB (the
+	 * standard map, plus the low map on AN1/2 - see bf_xpoint_write's
+	 * own comment for why AN1/2 needs both).  The addresses use the
+	 * source's idx_l/idx_r on the canonical block - writing the raw
+	 * index on both bases would put PB1 R on the L side and PB1 L on
+	 * the R side (L+R on both = mono).  The "cross" registers
+	 * (L-reg idx_r / R-reg idx_l) are left at 0; the restore at stream
+	 * start re-writes the same addresses from the cache.
+	 */
+	for (out = 0; out < 6; out++) {
+		unsigned int blk = bf_xpoint_block[out];
+
+		for (src = 0; src < 14; src++) {
+			ret = bf_xpoint_write(chip, out, src, BF_FADER_0DB,
+					      BF_FADER_0DB);
+			if (ret < 0)
+				return ret;
+		}
+		ret = bf_crosspoint_clear_cross(chip, blk);
+		if (ret < 0)
+			return ret;
+	}
+
+	/* Mirror the defaults into the control cache (14 controls/output). */
+	for (out = 0; out < 6; out++)
+		for (src = 0; src < 14; src++) {
+			chip->xpoint[out][src][0] = BF_FADER_0DB;
+			chip->xpoint[out][src][1] = BF_FADER_0DB;
+		}
+
+	/* Host settings word - bf_settings_write() is Internal-only at
+	 * this point in the series (the clock-source control lands with
+	 * a later patch).
+	 */
+	return bf_settings_write(chip);
+}
+
+/* The device resets its output masters to mute when a stream session
+ * starts (hardware-verified 2026-08-24: after a stream start the
+ * output stays silent until a master write lands - only a write
+ * un-mutes the 8-bit register).  Re-apply the six output masters +
+ * mutes from the cache; also used by the PM restore path.
+ */
+int bf_apply_masters(struct snd_usb_babyface *chip)
+{
+	int out, ret;
+	u16 flag;
+
+	for (out = 0; out < 6; out++) {
+		u16 l = chip->muted[out] ? 0 : chip->master[out][0];
+		u16 r = chip->muted[out] ? 0 : chip->master[out][1];
+		u8 l8 = chip->muted[out] ? BF_MASTER_MUTE : bf_master_8bit(l);
+		u8 r8 = chip->muted[out] ? BF_MASTER_MUTE : bf_master_8bit(r);
+
+		ret = bf_vendor_write(chip, BF_REQ_GAIN, l8,
+				      BF_REG_MASTER_8 + 2 * out);
+		if (ret < 0)
+			return ret;
+		ret = bf_vendor_write(chip, BF_REQ_GAIN, r8,
+				      BF_REG_MASTER_8 + 2 * out + 1);
+		if (ret < 0)
+			return ret;
+		flag = bf_flag_cycle[chip->flag_cnt];
+		chip->flag_cnt = (chip->flag_cnt + 1) & 3;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, l,
+				      (BF_REG_MASTER_16 + 2 * out) | flag);
+		if (ret < 0)
+			return ret;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, r,
+				      (BF_REG_MASTER_16 + 2 * out + 1) | flag);
+		if (ret < 0)
+			return ret;
+	}
+	return 0;
+}
+
+/* -- mixer controls ------------------------ */
+
+/* dB TLV for the output masters: 0x2000 = 0 dB, 0x4000 = +6 dB
+ * (CALIBRATION.md) with the hardware 20*log10(v/0x2000) law - the raw
+ * 16-bit value IS the linear amplitude.  WirePlumber needs this to map
+ * the volume 1:1 to the hardware control instead of applying a software
+ * volume on top (which left the output ~30 dB down).
+ */
+static const DECLARE_TLV_DB_RANGE(bf_master_tlv,
+	0, 0x2000, TLV_DB_LINEAR_ITEM(-6500, 0),
+	0x2000, 0x4000, TLV_DB_LINEAR_ITEM(0, 600)
+);
+
+static int bf_master_info(struct snd_kcontrol *kctl,
+			  struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 2;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = 0x4000;	/* +6 dB = 2 x 0dB(0x2000) */
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int bf_master_get(struct snd_kcontrol *kctl,
+			 struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_usb_babyface *chip = snd_kcontrol_chip(kctl);
+	int out = bf_master_out[kctl->private_value];
+
+	ucontrol->value.integer.value[0] = chip->master[out][0];
+	ucontrol->value.integer.value[1] = chip->master[out][1];
+	return 0;
+}
+
+static int bf_master_put(struct snd_kcontrol *kctl,
+			 struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_usb_babyface *chip = snd_kcontrol_chip(kctl);
+	int out = bf_master_out[kctl->private_value];
+	u16 l = ucontrol->value.integer.value[0];
+	u16 r = ucontrol->value.integer.value[1];
+	u16 flag;
+	int ret = 0;
+
+	/* The control is declared 0..0x4000 (+6 dB); reject anything outside
+	 * so the 16-bit companion register and the cache stay in spec (the
+	 * ALSA core only enforces this with CONFIG_SND_CTL_INPUT_VALIDATION).
+	 */
+	if (l > 0x4000 || r > 0x4000)
+		return -EINVAL;
+
+	mutex_lock(&chip->mutex);
+	if (l == chip->master[out][0] && r == chip->master[out][1])
+		goto out;
+
+	flag = bf_flag_cycle[chip->flag_cnt];
+	chip->flag_cnt = (chip->flag_cnt + 1) & 3;
+
+	/* The 8-bit register is the real volume; the 16-bit is its
+	 * companion (kept in sync like TotalMix).
+	 */
+	ret = bf_vendor_write(chip, BF_REQ_GAIN, bf_master_8bit(l),
+			      BF_REG_MASTER_8 + 2 * out);
+	if (ret < 0)
+		goto out;
+	ret = bf_vendor_write(chip, BF_REQ_GAIN, bf_master_8bit(r),
+			      BF_REG_MASTER_8 + 2 * out + 1);
+	if (ret < 0)
+		goto out;
+	ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, l,
+			      (BF_REG_MASTER_16 + 2 * out) | flag);
+	if (ret < 0)
+		goto out;
+	ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, r,
+			      (BF_REG_MASTER_16 + 2 * out + 1) | flag);
+	if (ret < 0)
+		goto out;
+
+	chip->master[out][0] = l;
+	chip->master[out][1] = r;
+	chip->muted[out] = false;
+	/* The DIM engaged/dim_saved re-base hook lands with the DIM
+	 * switch (a later patch in this series) - chip->dim does not
+	 * exist yet at this point in the split.
+	 */
+	ret = 1;
+out:
+	mutex_unlock(&chip->mutex);
+	return ret;
+}
+
+static int bf_mute_info(struct snd_kcontrol *kctl,
+			struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_BOOLEAN;
+	uinfo->count = 2;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = 1;
+	return 0;
+}
+
+static int bf_mute_get(struct snd_kcontrol *kctl,
+		       struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_usb_babyface *chip = snd_kcontrol_chip(kctl);
+	int out = bf_master_out[kctl->private_value];
+
+	/* ALSA convention: 1 = enabled (sound on) = not muted. */
+	ucontrol->value.integer.value[0] = !chip->muted[out];
+	ucontrol->value.integer.value[1] = !chip->muted[out];
+	return 0;
+}
+
+static int bf_mute_put(struct snd_kcontrol *kctl,
+		       struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_usb_babyface *chip = snd_kcontrol_chip(kctl);
+	int out = bf_master_out[kctl->private_value];
+	bool muted = !ucontrol->value.integer.value[0];
+	u16 flag;
+	int ret = 0;
+
+	mutex_lock(&chip->mutex);
+	if (muted == chip->muted[out])
+		goto out;
+
+	flag = bf_flag_cycle[chip->flag_cnt];
+	chip->flag_cnt = (chip->flag_cnt + 1) & 3;
+
+	if (muted) {
+		ret = bf_vendor_write(chip, BF_REQ_GAIN, BF_MASTER_MUTE,
+				      BF_REG_MASTER_8 + 2 * out);
+		if (ret < 0)
+			goto out;
+		ret = bf_vendor_write(chip, BF_REQ_GAIN, BF_MASTER_MUTE,
+				      BF_REG_MASTER_8 + 2 * out + 1);
+		if (ret < 0)
+			goto out;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, 0x0000,
+				      (BF_REG_MASTER_16 + 2 * out) | flag);
+		if (ret < 0)
+			goto out;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, 0x0000,
+				      (BF_REG_MASTER_16 + 2 * out + 1) | flag);
+		if (ret < 0)
+			goto out;
+	} else {
+		/* Unmute restores the cached volume (TotalMix keeps the
+		 * pre-mute fader value host-side), 8-bit + 16-bit.
+		 */
+		ret = bf_vendor_write(chip, BF_REQ_GAIN,
+				      bf_master_8bit(chip->master[out][0]),
+				      BF_REG_MASTER_8 + 2 * out);
+		if (ret < 0)
+			goto out;
+		ret = bf_vendor_write(chip, BF_REQ_GAIN,
+				      bf_master_8bit(chip->master[out][1]),
+				      BF_REG_MASTER_8 + 2 * out + 1);
+		if (ret < 0)
+			goto out;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT,
+				      chip->master[out][0],
+				      (BF_REG_MASTER_16 + 2 * out) | flag);
+		if (ret < 0)
+			goto out;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT,
+				      chip->master[out][1],
+				      (BF_REG_MASTER_16 + 2 * out + 1) | flag);
+		if (ret < 0)
+			goto out;
+	}
+	chip->muted[out] = muted;
+	ret = 1;
+out:
+	mutex_unlock(&chip->mutex);
+	return ret;
+}
+
+/* -- crosspoint matrix (6 outputs x 14 sources) -------------- */
+
+/* The crosspoint fader is linear in amplitude: BF_FADER_0DB (0x16a0) is
+ * unity and BF_FADER_TOP (0x2d41) is exactly twice that, i.e. +6 dB - see
+ * bf_fader_curve, whose whole span follows raw = BF_FADER_0DB * 10^(dB/20).
+ * Raw 0 is off.
+ */
+static const DECLARE_TLV_DB_LINEAR(bf_xpoint_tlv, TLV_DB_GAIN_MUTE, 600);
+
+/* Write a crosspoint slot on the wire: the standard map always, and -
+ * for the AN1/2 output only - the low map as well.
+ *
+ * HARDWARE-VERIFIED 2026-09-14: AN1/2 is not just another output with
+ * a redundant "shadow" register, despite what this file used to say.
+ * Sweeping only the standard map (BF_REG_CROSS_BASE_*) into AN1/2
+ * produced no audible change at all, off through +6 dB, with two
+ * independent sources (a generated tone via PB1, a live mic via AN2);
+ * the exact same code path targeting any other output (verified on
+ * PH3/4) tracked the fader correctly, off to +6 dB within 0.6 dB.
+ * PROTOCOL.md's "Scene load" capture explains why: the vendor software
+ * always writes BOTH the standard map and the low map
+ * (BF_REG_LOWMAP_BASE_*) together for AN1/2's own crosspoints, at the
+ * same value - the low map is what actually feeds that output's sum;
+ * the standard map alone is not enough. Every other output only has a
+ * standard map.
+ *
+ * bf_split_apply() already knew this (it writes both for AN1/2's
+ * playback pairs); this generalises the same pattern to the plain
+ * fader.
+ */
+int bf_xpoint_write(struct snd_usb_babyface *chip, int out, int src,
+		    u16 l, u16 r)
+{
+	unsigned int blk = bf_xpoint_block[out];
+	const struct bf_source *s = &bf_sources[src];
+	u16 flag;
+	int ret;
+
+	if (out == 0) {
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, l,
+				      BF_REG_LOWMAP_BASE_L + s->idx_l);
+		if (ret < 0)
+			return ret;
+		ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, r,
+				      BF_REG_LOWMAP_BASE_R + s->idx_r);
+		if (ret < 0)
+			return ret;
+	}
+
+	flag = bf_flag_cycle[chip->flag_cnt];
+	chip->flag_cnt = (chip->flag_cnt + 1) & 3;
+	ret = bf_vendor_write(chip, BF_REQ_CROSSPOINT, l,
+			      (BF_REG_CROSS_BASE_L + BF_REG_CROSS_STRIDE * blk +
+			       s->idx_l) | flag);
+	if (ret < 0)
+		return ret;
+	return bf_vendor_write(chip, BF_REQ_CROSSPOINT, r,
+			       (BF_REG_CROSS_BASE_R + BF_REG_CROSS_STRIDE * blk +
+				s->idx_r) | flag);
+}
+
+static int bf_xpoint_info(struct snd_kcontrol *kctl,
+			  struct snd_ctl_elem_info *uinfo)
+{
+	uinfo->type = SNDRV_CTL_ELEM_TYPE_INTEGER;
+	uinfo->count = 2;
+	uinfo->value.integer.min = 0;
+	uinfo->value.integer.max = BF_FADER_TOP;	/* +6 dB fader top */
+	uinfo->value.integer.step = 1;
+	return 0;
+}
+
+static int bf_xpoint_get(struct snd_kcontrol *kctl,
+			 struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_usb_babyface *chip = snd_kcontrol_chip(kctl);
+	int out = kctl->private_value >> 8;
+	int src = kctl->private_value & 0xff;
+
+	ucontrol->value.integer.value[0] = chip->xpoint[out][src][0];
+	ucontrol->value.integer.value[1] = chip->xpoint[out][src][1];
+	return 0;
+}
+
+static int bf_xpoint_put(struct snd_kcontrol *kctl,
+			 struct snd_ctl_elem_value *ucontrol)
+{
+	struct snd_usb_babyface *chip = snd_kcontrol_chip(kctl);
+	int out = kctl->private_value >> 8;
+	int src = kctl->private_value & 0xff;
+	u16 l = ucontrol->value.integer.value[0];
+	u16 r = ucontrol->value.integer.value[1];
+	int ret = 0;
+
+	if (l > BF_FADER_TOP || r > BF_FADER_TOP)
+		return -EINVAL;
+
+	mutex_lock(&chip->mutex);
+	if (l == chip->xpoint[out][src][0] && r == chip->xpoint[out][src][1])
+		goto out;
+
+	ret = bf_xpoint_write(chip, out, src, l, r);
+	if (ret < 0)
+		goto out;
+
+	chip->xpoint[out][src][0] = l;
+	chip->xpoint[out][src][1] = r;
+	ret = 1;
+out:
+	mutex_unlock(&chip->mutex);
+	return ret;
+}
+
+int babyface_create_xpoints(struct snd_usb_babyface *chip)
+{
+	struct snd_kcontrol *kctl;
+	int out, src, err;
+
+	for (out = 0; out < 6; out++) {
+		for (src = 0; src < 14; src++) {
+			kctl = snd_ctl_new1(&(struct snd_kcontrol_new){
+				.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+				.name = "Playback Volume",
+				.index = out * 14 + src,
+				.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+					  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+				.info = bf_xpoint_info,
+				.get = bf_xpoint_get,
+				.put = bf_xpoint_put,
+				.tlv.p = bf_xpoint_tlv,
+				.private_value = (out << 8) | src,
+			}, chip);
+			/* Name the control by its source: "AN1 Playback Volume",
+			 * "PB1 Playback Volume"... with a unique index.
+			 */
+			strscpy(kctl->id.name, bf_sources[src].name,
+				sizeof(kctl->id.name));
+			strlcat(kctl->id.name, " Playback Volume",
+				sizeof(kctl->id.name));
+			err = snd_ctl_add(chip->card, kctl);
+			if (err < 0)
+				return err;
+		}
+	}
+
+	return 0;
+}
+
+int babyface_create_masters(struct snd_usb_babyface *chip)
+{
+	static const char * const out_names[6] = {
+		"AN1/2", "PH3/4", "AS1/2", "ADAT3/4", "ADAT5/6", "ADAT7/8"
+	};
+	struct snd_kcontrol *kctl;
+	int i, err;
+
+	for (i = 0; i < 6; i++) {
+		kctl = snd_ctl_new1(&(struct snd_kcontrol_new){
+			.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+			.name = out_names[i],
+			.index = i,
+			.access = SNDRV_CTL_ELEM_ACCESS_READWRITE |
+				  SNDRV_CTL_ELEM_ACCESS_TLV_READ,
+			.info = bf_master_info,
+			.get = bf_master_get,
+			.put = bf_master_put,
+			.tlv.p = bf_master_tlv,
+			.private_value = i,
+		}, chip);
+		strlcat(kctl->id.name, " Playback Volume", sizeof(kctl->id.name));
+		err = snd_ctl_add(chip->card, kctl);
+		if (err < 0)
+			return err;
+
+		kctl = snd_ctl_new1(&(struct snd_kcontrol_new){
+			.iface = SNDRV_CTL_ELEM_IFACE_MIXER,
+			.name = out_names[i],
+			.index = i,
+			.info = bf_mute_info,
+			.get = bf_mute_get,
+			.put = bf_mute_put,
+			.private_value = i,
+		}, chip);
+		strlcat(kctl->id.name, " Playback Switch", sizeof(kctl->id.name));
+		err = snd_ctl_add(chip->card, kctl);
+		if (err < 0)
+			return err;
+
+		dev_dbg(&chip->dev->dev, "output %d = %s\n", i, out_names[i]);
+	}
+
+	return 0;
+}
+
diff --git a/sound/usb/babyfacepro/babyfacepro.c b/sound/usb/babyfacepro/babyfacepro.c
index 2d71286e3..50b6a31a5 100644
--- a/sound/usb/babyfacepro/babyfacepro.c
+++ b/sound/usb/babyfacepro/babyfacepro.c
@@ -3,13 +3,16 @@
  * RME Babyface Pro / Pro FS - proprietary-mode USB audio driver
  *
  * Core driver: USB vendor requests + cold init, interrupt-URB PCM
- * streaming, and the card lifecycle (probe/disconnect/module entry).
- * No mixer controls, front-panel support or suspend/resume yet - see
- * babyfacepro.h and the cover letter for the rest of the series.
+ * streaming, mixer-state persistence across re-probes/resume, and the
+ * card lifecycle (probe/disconnect/module entry).  See babyfacepro.h
+ * for the shared device state and register map, and babyfacepro-ctl.c
+ * for the ALSA control surface (mixer, front panel, DSP EQ - added by
+ * later patches in this series).
  */
 #include <linux/math64.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
+#include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/unaligned.h>
 #include <linux/usb.h>
@@ -252,6 +255,139 @@ int bf_cold_init(struct snd_usb_babyface *chip)
 	return 0;
 }
 
+/* -- mixer-state persistence across interface re-probes --------
+ * A userspace client can claim the proprietary interface via usbfs
+ * (USBDEVFS_DISCONNECT_CLAIM - seen with PipeWire grabbing the
+ * device when a stream targets the sink, and with the TuxMix
+ * user-space daemon's libusb).  That detaches us and the card
+ * disappears for the duration; on release the interface re-probes.
+ * The device keeps its registers across the detach, but our cold
+ * init clears them - so save the mixer state at disconnect and
+ * restore it at the next probe.
+ */
+
+static LIST_HEAD(bf_saved_list);
+static DEFINE_MUTEX(bf_saved_mutex);
+
+/* Re-apply the whole cached mixer state after a resume (the device
+ * lost its registers across a system suspend - TotalMix does the same
+ * re-apply).  Caller holds chip->mutex.
+ *
+ * Only the masters and the crosspoint matrix exist at this point in
+ * the series; preamp/gain and pitch are re-applied here too once the
+ * later patches that introduce them land.
+ */
+int babyface_restore_state(struct snd_usb_babyface *chip)
+{
+	int out, src, ret;
+
+	/* Masters (8-bit = the real volume) + mutes. */
+	ret = bf_apply_masters(chip);
+	if (ret < 0)
+		return ret;
+
+	/* Crosspoints (canonical out -> register block; AN1/2 also needs
+	 * the low map, see bf_xpoint_write's own comment).
+	 */
+	for (out = 0; out < 6; out++) {
+		unsigned int blk = bf_xpoint_block[out];
+
+		for (src = 0; src < 14; src++) {
+			ret = bf_xpoint_write(chip, out, src,
+					      chip->xpoint[out][src][0],
+					      chip->xpoint[out][src][1]);
+			if (ret < 0)
+				return ret;
+		}
+		ret = bf_crosspoint_clear_cross(chip, blk);
+		if (ret < 0)
+			return ret;
+	}
+	/* The rate (family register), then the varispeed ratio, which is
+	 * sticky in the device and so must be re-sent even at pitch 0 in
+	 * case something else wrote it while we were detached.
+	 */
+	ret = bf_clock_write(chip);
+	if (ret < 0)
+		return ret;
+	return bf_pitch_write(chip, chip->pitch);
+}
+
+void bf_state_save(struct snd_usb_babyface *chip)
+{
+	struct bf_saved *s;
+	const char *key = chip->dev->serial ? chip->dev->serial :
+			  dev_name(&chip->dev->dev);
+	bool found = false;
+
+	mutex_lock(&bf_saved_mutex);
+	list_for_each_entry(s, &bf_saved_list, list) {
+		if (strcmp(s->key, key))
+			continue;
+		found = true;
+		break;
+	}
+	if (!found) {
+		s = kzalloc_obj(*s, GFP_KERNEL);
+		if (!s) {
+			mutex_unlock(&bf_saved_mutex);
+			return;
+		}
+		strscpy(s->key, key, sizeof(s->key));
+		list_add_tail(&s->list, &bf_saved_list);
+	}
+
+	s->flag_cnt = chip->flag_cnt;
+	memcpy(s->master, chip->master, sizeof(s->master));
+	memcpy(s->muted, chip->muted, sizeof(s->muted));
+	memcpy(s->xpoint, chip->xpoint, sizeof(s->xpoint));
+	mutex_unlock(&bf_saved_mutex);
+}
+
+/* Copy a saved state (if any) into a freshly probed chip and push it
+ * to the device.  Returns 1 when restored, -ENOENT when there is none,
+ * or a negative error from the vendor writes.
+ */
+int bf_state_restore(struct snd_usb_babyface *chip)
+{
+	struct bf_saved *s;
+	const char *key = chip->dev->serial ? chip->dev->serial :
+			  dev_name(&chip->dev->dev);
+	int ret = -ENOENT;
+
+	mutex_lock(&bf_saved_mutex);
+	list_for_each_entry(s, &bf_saved_list, list) {
+		if (strcmp(s->key, key))
+			continue;
+		chip->flag_cnt = s->flag_cnt;
+		memcpy(chip->master, s->master, sizeof(chip->master));
+		memcpy(chip->muted, s->muted, sizeof(chip->muted));
+		memcpy(chip->xpoint, s->xpoint, sizeof(chip->xpoint));
+		ret = 1;
+		break;
+	}
+	mutex_unlock(&bf_saved_mutex);
+	if (ret != 1)
+		return ret;
+
+	mutex_lock(&chip->mutex);
+	ret = babyface_restore_state(chip);
+	mutex_unlock(&chip->mutex);
+	return ret ? ret : 1;
+}
+
+void bf_state_purge(void)
+{
+	struct bf_saved *s, *tmp;
+
+	mutex_lock(&bf_saved_mutex);
+	list_for_each_entry_safe(s, tmp, &bf_saved_list, list) {
+		list_del(&s->list);
+		kfree(s);
+	}
+	mutex_unlock(&bf_saved_mutex);
+}
+
 /* -- PCM data path ------------------------- */
 
 static bool babyface_capture_copy(struct snd_usb_babyface *chip,
@@ -640,6 +776,14 @@ void babyface_stream_work(struct work_struct *work)
 		if (ret < 0)
 			goto err;
 
+		/* The cold init above cleared the mixer registers; push the
+		 * cached masters and crosspoints back so the session starts
+		 * at the user's levels.
+		 */
+		ret = babyface_restore_state(chip);
+		if (ret < 0)
+			goto err;
+
 		chip->streaming = true;
 		dev_dbg(&chip->dev->dev, "stream started (%u frames/URB, %u URBs)\n",
 			chip->frames_per_urb, chip->nurbs);
@@ -1063,6 +1207,26 @@ static int babyface_probe(struct usb_interface *intf,
 		goto error;
 	}
 
+	/* Restore the mixer state saved at the last disconnect (if any);
+	 * the device keeps its registers across a usbfs detach, but the
+	 * cold init above cleared them, so push the user's settings back.
+	 */
+	err = bf_state_restore(chip);
+	if (err == -ENOENT) {
+		/* No saved state: the 0x16 clear zeroed the mixer registers,
+		 * so restore the factory default routing to keep the outputs
+		 * live out of the box.
+		 */
+		err = babyface_write_default_mixer(chip);
+		if (err < 0) {
+			dev_err(&intf->dev, "default mixer restore failed: %d\n", err);
+			goto error;
+		}
+	} else if (err < 0) {
+		dev_err(&intf->dev, "mixer state restore failed: %d\n", err);
+		goto error;
+	}
+
 	/* Keep the allocation size independent of the active USB mode. */
 	urbsize = BF_WORDS_PER_FRAME * sizeof(u32) * chip->frames_per_urb;
 	chip->urbs_in = kcalloc(chip->nurbs, sizeof(*chip->urbs_in), GFP_KERNEL);
@@ -1107,6 +1271,18 @@ static int babyface_probe(struct usb_interface *intf,
 		goto error;
 	}
 
+	err = babyface_create_masters(chip);
+	if (err < 0) {
+		dev_err(&intf->dev, "master control creation failed: %d\n", err);
+		goto error;
+	}
+
+	err = babyface_create_xpoints(chip);
+	if (err < 0) {
+		dev_err(&intf->dev, "crosspoint creation failed: %d\n", err);
+		goto error;
+	}
+
 	err = snd_card_register(chip->card);
 	if (err < 0) {
 		dev_err(&intf->dev, "snd_card_register failed: %d\n", err);
@@ -1144,6 +1320,12 @@ static void babyface_disconnect(struct usb_interface *intf)
 	if (chip->shutdown)
 		return;
 
+	/* Keep the mixer state for the next probe: a userspace usbfs
+	 * claim (PipeWire sink grab, TuxMix daemon) detaches us and the
+	 * cold init of the re-probe would otherwise wipe the settings.
+	 */
+	bf_state_save(chip);
+
 	chip->shutdown = true;
 	cancel_work_sync(&chip->stream_work);
 	/* Balance the probe()-time usb_disable_autosuspend(): the usb_device
@@ -1189,6 +1371,7 @@ static int __init babyface_init(void)
 
 static void __exit babyface_exit(void)
 {
+	bf_state_purge();
 	usb_deregister(&babyface_driver);
 }
 
diff --git a/sound/usb/babyfacepro/babyfacepro.h b/sound/usb/babyfacepro/babyfacepro.h
index de0353a59..6125e763f 100644
--- a/sound/usb/babyfacepro/babyfacepro.h
+++ b/sound/usb/babyfacepro/babyfacepro.h
@@ -12,8 +12,12 @@
  * snd-usb-audio quirk.
  *
  * This file and babyfacepro.c cover the card lifecycle (probe,
- * disconnect) and the PCM stream only - no mixer controls, no
- * front-panel support, no suspend/resume yet.  Those are added by
+ * disconnect), the PCM stream, and mixer-state persistence across
+ * re-probes/resume.  babyfacepro-ctl.c adds the ALSA control surface,
+ * starting with the output masters (volume + mute) and the crosspoint
+ * routing matrix - the minimum needed for the card to produce
+ * controllable, routed audio.  Preamp/gain, the routing-flag switches,
+ * varispeed pitch, front-panel support and suspend/resume are added by
  * later patches in this series, each with its own register map and
  * device-state additions; see the cover letter for the full series
  * plan.
@@ -81,8 +85,10 @@
  * panel and DSP EQ patches each add their own as those features land.
  */
 #define BF_REQ_KEEPALIVE		0x10	/* settings word / stream trigger */
+#define BF_REQ_CROSSPOINT		0x12	/* 16-bit crosspoint / master */
 #define BF_REQ_REG_CLEAR		0x16	/* cold-init register clear */
 #define BF_REQ_PREAMP			0x17	/* 48V/PAD state + readback */
+#define BF_REQ_GAIN			0x1a	/* 8-bit gain / master companion */
 #define BF_REQ_DDS			0x1b	/* clock quads */
 #define BF_REQ_STATUS_2			0x1c	/* read 4 B */
 #define BF_REQ_SESSION_START		0x1d
@@ -108,6 +114,72 @@
 #define BF_SETTINGS_CLOCK_INTERNAL	0x0001
 #define BF_SETTINGS_CLOCK_OPTICAL	0x0004
 
+/* Register addresses (masters + crosspoint matrix). */
+#define BF_REG_MASTER_16		0x03e0	/* + 2*out (bReq 0x12) */
+#define BF_REG_MASTER_8			0x0004	/* + 2*out (bReq 0x1a) */
+#define BF_REG_CROSS_BASE_L		0x0034	/* + 0x34*out + src (bReq 0x12) */
+#define BF_REG_CROSS_BASE_R		0x004e	/* + 0x34*out + src */
+#define BF_REG_CROSS_STRIDE		0x0034
+/* Low map (the AN1/2 monitor bus's own per-source registers, one set
+ * shared across every output - not one per output block like the
+ * standard crosspoint map above). NOT a shadow/mirror of the standard
+ * map for AN1/2: it is what that output actually sums from, and the
+ * standard map alone has no audible effect on it (hardware-verified
+ * 2026-09-14, see bf_xpoint_write's own comment and KERNEL-DRIVER.md).
+ */
+#define BF_REG_LOWMAP_BASE_L		0x0000	/* + idx_l */
+#define BF_REG_LOWMAP_BASE_R		0x001a	/* + idx_r */
+
+/* The "cross" register block within each output: the L-registers sit at
+ * odd offsets 5..23 and the R-registers at even offsets 4..22 (the stereo
+ * source pairs that can be cross-linked).  bf_crosspoint_clear_cross()
+ * zeroes them because the cold-init clear does not cover them.
+ */
+#define BF_CROSS_L_FIRST		5
+#define BF_CROSS_L_LAST			23
+#define BF_CROSS_R_FIRST		4
+#define BF_CROSS_R_LAST			22
+
+/* Calibrated master value: 0 dB = 0x2000 (+6 dB = 0x4000).  See
+ * CALIBRATION.md.  The crosspoint fader curve is DIFFERENT (0 dB =
+ * 0x16a0, top 0x2d41 - see below).
+ */
+#define BF_MASTER_0DB			0x2000
+
+/* The 8-bit master is the REAL output volume (hardware-verified
+ * 2026-08-24: writing it changes the level, the 16-bit does not).
+ * Scale: 0.5 dB per step, 0xf3 = 0 dB (the scene-load default),
+ * bottom 0x73 = -64 dB (silence), top 0xff = +6 dB.  The 16-bit
+ * register is a companion kept in sync (TotalMix writes both).
+ * The mute value is 0x3B.
+ */
+#define BF_MASTER_8_0DB			0xf3
+#define BF_MASTER_8_MIN			0x73
+#define BF_MASTER_MUTE			0x3b
+#define BF_MASTER_UNMUTE		0xf3
+/* -20 dB master, 8-bit and 16-bit: the exact pair the hardware DIM
+ * button writes (cap_dim2.pcap), reused as the power-on default.
+ */
+#define BF_MASTER_MINUS20_8		0xcb
+#define BF_MASTER_MINUS20_16		0x0333
+
+/* Crosspoint fader curve: 0 dB = 0x16a0, +6 dB = 0x2d41 (fader curve,
+ * DIFFERENT from the master 0x4000 top - see CALIBRATION.md).
+ */
+#define BF_FADER_0DB			0x16a0
+#define BF_FADER_TOP			0x2d41
+
+/* The crosspoint matrix sources (14 controls per output). */
+struct bf_source {
+	const char *name;
+	u8 idx_l;
+	u8 idx_r;
+};
+
+/* Crosspoint-source order + register block maps (babyfacepro-ctl.c). */
+extern const struct bf_source bf_sources[14];
+extern const u8 bf_xpoint_block[6];
+
 struct snd_usb_babyface {
 	struct snd_card *card;
 	struct usb_device *dev;
@@ -138,6 +210,26 @@ struct snd_usb_babyface {
 	struct snd_pcm_substream *subs[2];
 	unsigned long hw_ptr[2];
 	unsigned long prev_period[2];
+
+	/* mixer state (no gain readback exists - host-side mirror) */
+	u8 flag_cnt;			/* 0xc000/0x4000/0x8000/0x0000 */
+	u16 master[6][2];		/* cached 16-bit masters */
+	bool muted[6];
+	u16 xpoint[6][14][2];		/* cached crosspoints (out, src, L/R) */
+};
+
+/* The mixer state cached across interface re-probes/resume (see
+ * babyfacepro.c's own comment on bf_state_save/bf_state_restore).
+ * Grows alongside struct snd_usb_babyface as later patches in this
+ * series add more mixer state to persist.
+ */
+struct bf_saved {
+	struct list_head list;
+	char key[32];
+	u8 flag_cnt;
+	u16 master[6][2];
+	bool muted[6];
+	u16 xpoint[6][14][2];
 };
 
 struct bf_rate {
@@ -163,3 +255,28 @@ void babyface_stream_kill(struct snd_usb_babyface *chip);
 void babyface_pcm_stop_both(struct snd_usb_babyface *chip, snd_pcm_state_t state);
 void babyface_stream_work(struct work_struct *work);
 extern const struct snd_pcm_hw_constraint_list bf_rates_constraint;
+
+/* Mixer-state persistence across interface re-probes/resume. */
+void bf_state_save(struct snd_usb_babyface *chip);
+int bf_state_restore(struct snd_usb_babyface *chip);
+void bf_state_purge(void);
+int babyface_restore_state(struct snd_usb_babyface *chip);
+
+/* -- babyfacepro-ctl.c ----------------------- */
+extern const u16 bf_flag_cycle[4];
+int bf_vendor_write_cycle(struct snd_usb_babyface *chip, u8 req, u16 val, u16 idx);
+int bf_crosspoint_clear_cross(struct snd_usb_babyface *chip,
+			      unsigned int blk);
+int babyface_write_default_mixer(struct snd_usb_babyface *chip);
+int bf_apply_masters(struct snd_usb_babyface *chip);
+int bf_xpoint_write(struct snd_usb_babyface *chip, int out, int src,
+		    u16 l, u16 r);
+int babyface_create_masters(struct snd_usb_babyface *chip);
+int babyface_create_xpoints(struct snd_usb_babyface *chip);
+
+/* Master gain-law helpers - shared with the front-panel wheels once
+ * the front panel lands.
+ */
+int bf_master_half_db(u16 vol16);	/* 16-bit master -> dBx2 */
+int bf_master_16bit(int half_db);	/* dBx2 -> 16-bit master */
+u8 bf_master_8bit(u16 vol16);		/* 16-bit master -> 8-bit companion */
-- 
2.55.0