[PATCH] ALSA: hda/realtek: Fix the Dell XPS 8940 headset microphone

[Angel J <iamanaws@httpd.dev>]

The Dell XPS 8940 (1028:09c5) has an ALC3861 codec (0x10ec0899).
Its BIOS marks the headset microphone pin at NID 0x19 as disconnected
(0x411111f0). With no external microphone input in the pin configuration,
the generic parser creates a shared headphone/mic input on NID 0x1b
instead. Headphone playback works, but the headset microphone is silent.

Override NID 0x19 as a front microphone without independent presence
detection. This gives the generic parser the dedicated microphone
input and preserves NID 0x1b for simultaneous headphone playback.

I encountered this issue on my XPS 8940. Similar symptoms were also
reported by a user on Ubuntu:
https://bugs.launchpad.net/bugs/1971232

Cc: stable@vger.kernel.org
Assisted-by: Codex (GPT-6.1 Sol)
Signed-off-by: Angel J <iamanaws@httpd.dev>
---

Notes:
    Build-tested alc882.o with x86_64 defconfig, GCC 16.2.0 and W=1
    without warnings. The patch also applies to upstream v6.18.

    Boot-tested on a Dell XPS 8940 running Linux 6.18.58.
    Microphone capture and headphone playback work simultaneously.

 sound/hda/codecs/realtek/alc882.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/sound/hda/codecs/realtek/alc882.c b/sound/hda/codecs/realtek/alc882.c
index 800c3d6f5..cf8d3c48e 100644
--- a/sound/hda/codecs/realtek/alc882.c
+++ b/sound/hda/codecs/realtek/alc882.c
@@ -50,6 +50,7 @@ enum {
 	ALC889_FIXUP_MP41_VREF,
 	ALC882_FIXUP_INV_DMIC,
 	ALC882_FIXUP_NO_PRIMARY_HP,
+	ALC898_FIXUP_DELL_XPS8940_MIC,
 	ALC887_FIXUP_ASUS_BASS,
 	ALC887_FIXUP_BASS_CHMAP,
 	ALC1220_FIXUP_GB_DUAL_CODECS,
@@ -507,6 +508,13 @@ static const struct hda_fixup alc882_fixups[] = {
 		.type = HDA_FIXUP_FUNC,
 		.v.func = alc882_fixup_no_primary_hp,
 	},
+	[ALC898_FIXUP_DELL_XPS8940_MIC] = {
+		.type = HDA_FIXUP_PINS,
+		.v.pins = (const struct hda_pintbl[]) {
+			{ 0x19, 0x02a19130 }, /* headset mic, no separate jack detect */
+			{}
+		},
+	},
 	[ALC887_FIXUP_ASUS_BASS] = {
 		.type = HDA_FIXUP_PINS,
 		.v.pins = (const struct hda_pintbl[]) {
@@ -610,6 +618,8 @@ static const struct hda_quirk alc882_fixup_tbl[] = {
 	SND_PCI_QUIRK(0x1025, 0x0259, "Acer Aspire 5935", ALC889_FIXUP_DAC_ROUTE),
 	SND_PCI_QUIRK(0x1025, 0x026b, "Acer Aspire 8940G", ALC882_FIXUP_ACER_ASPIRE_8930G),
 	SND_PCI_QUIRK(0x1025, 0x0296, "Acer Aspire 7736z", ALC882_FIXUP_ACER_ASPIRE_7736),
+	SND_PCI_QUIRK(0x1028, 0x09c5, "Dell XPS 8940",
+		      ALC898_FIXUP_DELL_XPS8940_MIC),
 	SND_PCI_QUIRK(0x1043, 0x13c2, "Asus A7M", ALC882_FIXUP_EAPD),
 	SND_PCI_QUIRK(0x1043, 0x1873, "ASUS W90V", ALC882_FIXUP_ASUS_W90V),
 	SND_PCI_QUIRK(0x1043, 0x1971, "Asus W2JC", ALC882_FIXUP_ASUS_W2JC),

base-commit: a4311e9447bbb219044db38897f95be112f46a8a