Comment 17 for bug 1252733

does the user manual or laptop specifovation mention about the support of conventional Mic with this combo Jack ?

if you using headset (TRRS), headset Mic pin 0x1b was set to vref50

 ,you may need to disable the Mic pin 0x1b when you using headphone (TRS) or unpluggef

On some machines, there is a headset jack that can support both
headphone, headsets (of both CTIA and OMTP type) and mic-in.

On other machines, the headset jack supports headphone, headsets
(both CTIA and OMTP), but not mic-in.

+ [ALC668_FIXUP_DELL_MIC_NO_PRESENCE] = {
+ .type = HDA_FIXUP_PINS,
+ .v.pins = (const struct hda_pintbl[]) {
+ { 0x19, 0x03a1913d }, /* use as headphone mic, without its own jack detect */
+ { 0x1b, 0x03a1113c }, /* use as headset mic, without its own jack detect */
+ { }
+ },
+ .chained = true,
+ .chain_id = ALC668_FIXUP_HEADSET_MODE
+ },
+ [ALC668_FIXUP_HEADSET_MODE] = {
+ .type = HDA_FIXUP_FUNC,
+ .v.func = alc_fixup_headset_mode_alc668,
+ },