[PATCH] ALSA: usb-audio: Add dB map quirk for Razer Barracuda X 2.4

The Razer Barracuda X 2.4 GHz USB headset dongle (0x1532:0x0552)
reports a minimum volume register value of cval->min = -16800.

In UAC 1/256 dB units, -16800 corresponds to -65.625 dB. However,
stock ALSA misinterprets this raw integer as 1/100 dB units
(-168.00 dB), causing user-space audio servers (PipeWire /
PulseAudio) to map their volume curves against an incorrectly wide
range.

Add an explicit usbmix_dB_map entry overriding Unit 2 to -6562
(-65.62 dB) to accurately report the physical hardware
attenuation bounds.

Signed-off-by: Markus Lindner <[email protected]>
---
 sound/usb/mixer_maps.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/sound/usb/mixer_maps.c b/sound/usb/mixer_maps.c
index faac7df1fb..4d8dca04f8 100644
--- a/sound/usb/mixer_maps.c
+++ b/sound/usb/mixer_maps.c
@@ -344,6 +344,16 @@ static const struct usbmix_name_map bose_soundlink_map[] = {
 	{ 0 }	/* terminator */
 };
 
+/*
+ * Razer Barracuda X 2.4: Firmware reports cval->min = -16800 in 1/256 dB units
+ * (-65.62 dB), which stock ALSA misinterprets as a -168 dB floor
+ */
+static const struct usbmix_dB_map razer_barracuda_x_2_4_dB = {-6562, 0};
+static const struct usbmix_name_map razer_barracuda_x_2_4_map[] = {
+	{ 2, NULL, .dB = &razer_barracuda_x_2_4_dB },
+	{ 0 }   /* terminator */
+};
+
 /* Sennheiser Communications Headset [PC 8], the dB value is reported as -6 negative maximum  */
 static const struct usbmix_dB_map sennheiser_pc8_dB = {-9500, 0};
 static const struct usbmix_name_map sennheiser_pc8_map[] = {
@@ -689,6 +699,11 @@ static const struct usbmix_ctl_map usbmix_ctl_maps[] = {
 		.id = USB_ID(0x17aa, 0x1046),
 		.map = lenovo_p620_rear_map,
 	},
+	{
+		/* Razer Barracuda X 2.4 */
+		.id = USB_ID(0x1532, 0x0552),
+		.map = razer_barracuda_x_2_4_map,
+	},
 	{
 		/* Sennheiser Communications Headset [PC 8] */
 		.id = USB_ID(0x1395, 0x0025),
-- 
2.47.3