4 files changed, 43 insertions, 12 deletions
diff --git a/sound/usb/mixer.c b/sound/usb/mixer.c
index f494dced3c11..4f85757009b3 100644
--- a/sound/usb/mixer.c
+++ b/sound/usb/mixer.c
@@ -1354,6 +1354,8 @@ static void build_feature_ctl(struct mixer_build *state, void *raw_desc,
 		}
 	}
 
+	snd_usb_mixer_fu_apply_quirk(state->mixer, cval, unitid, kctl);
+
 	range = (cval->max - cval->min) / cval->res;
 	/*
 	 * Are there devices with volume range more than 255? I use a bit more
diff --git a/sound/usb/mixer_maps.c b/sound/usb/mixer_maps.c
index 6a803eff87f7..ddca6547399b 100644
--- a/sound/usb/mixer_maps.c
+++ b/sound/usb/mixer_maps.c
@@ -348,13 +348,6 @@ static struct usbmix_name_map bose_companion5_map[] = {
 	{ 0 }	/* terminator */
 };
 
-/* Dragonfly DAC 1.2, the dB conversion factor is 1 instead of 256 */
-static struct usbmix_dB_map dragonfly_1_2_dB = {0, 5000};
-static struct usbmix_name_map dragonfly_1_2_map[] = {
-	{ 7, NULL, .dB = &dragonfly_1_2_dB },
-	{ 0 }	/* terminator */
-};
-
 /*
  * Control map entries
  */
@@ -470,11 +463,6 @@ static struct usbmix_ctl_map usbmix_ctl_maps[] = {
 		.id = USB_ID(0x05a7, 0x1020),
 		.map = bose_companion5_map,
 	},
-	{
-		/* Dragonfly DAC 1.2 */
-		.id = USB_ID(0x21b4, 0x0081),
-		.map = dragonfly_1_2_map,
-	},
 	{ 0 } /* terminator */
 };
 
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index fe91184ce832..0ce888dceed0 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -37,6 +37,7 @@
 #include <sound/control.h>
 #include <sound/hwdep.h>
 #include <sound/info.h>
+#include <sound/tlv.h>
 
 #include "usbaudio.h"
 #include "mixer.h"
@@ -1825,3 +1826,39 @@ void snd_usb_mixer_rc_memory_change(struct usb_mixer_interface *mixer,
 	}
 }
 
+static void snd_dragonfly_quirk_db_scale(struct usb_mixer_interface *mixer,
+					 struct snd_kcontrol *kctl)
+{
+	/* Approximation using 10 ranges based on output measurement on hw v1.2.
+	 * This seems close to the cubic mapping e.g. alsamixer uses. */
+	static const DECLARE_TLV_DB_RANGE(scale,
+		 0,  1, TLV_DB_MINMAX_ITEM(-5300, -4970),
+		 2,  5, TLV_DB_MINMAX_ITEM(-4710, -4160),
+		 6,  7, TLV_DB_MINMAX_ITEM(-3884, -3710),
+		 8, 14, TLV_DB_MINMAX_ITEM(-3443, -2560),
+		15, 16, TLV_DB_MINMAX_ITEM(-2475, -2324),
+		17, 19, TLV_DB_MINMAX_ITEM(-2228, -2031),
+		20, 26, TLV_DB_MINMAX_ITEM(-1910, -1393),
+		27, 31, TLV_DB_MINMAX_ITEM(-1322, -1032),
+		32, 40, TLV_DB_MINMAX_ITEM(-968, -490),
+		41, 50, TLV_DB_MINMAX_ITEM(-441, 0),
+	);
+
+	usb_audio_info(mixer->chip, "applying DragonFly dB scale quirk\n");
+	kctl->tlv.p = scale;
+	kctl->vd[0].access |= SNDRV_CTL_ELEM_ACCESS_TLV_READ;
+	kctl->vd[0].access &= ~SNDRV_CTL_ELEM_ACCESS_TLV_CALLBACK;
+}
+
+void snd_usb_mixer_fu_apply_quirk(struct usb_mixer_interface *mixer,
+				  struct usb_mixer_elem_info *cval, int unitid,
+				  struct snd_kcontrol *kctl)
+{
+	switch (mixer->chip->usb_id) {
+	case USB_ID(0x21b4, 0x0081): /* AudioQuest DragonFly */
+		if (unitid == 7 && cval->min == 0 && cval->max == 50)
+			snd_dragonfly_quirk_db_scale(mixer, kctl);
+		break;
+	}
+}
+
diff --git a/sound/usb/mixer_quirks.h b/sound/usb/mixer_quirks.h
index bdbfab093816..177c329cd4dd 100644
--- a/sound/usb/mixer_quirks.h
+++ b/sound/usb/mixer_quirks.h
@@ -9,5 +9,9 @@ void snd_emuusb_set_samplerate(struct snd_usb_audio *chip,
 void snd_usb_mixer_rc_memory_change(struct usb_mixer_interface *mixer,
 				    int unitid);
 
+void snd_usb_mixer_fu_apply_quirk(struct usb_mixer_interface *mixer,
+				  struct usb_mixer_elem_info *cval, int unitid,
+				  struct snd_kcontrol *kctl);
+
 #endif /* SND_USB_MIXER_QUIRKS_H */