Comment 24 for bug 893210

static const struct snd_kcontrol_new snd_ac97_ad1981x_jack_sense[] = {
 AC97_SINGLE("Headphone Jack Sense", AC97_AD_JACK_SPDIF, 11, 1, 0),
 AC97_SINGLE("Line Jack Sense", AC97_AD_JACK_SPDIF, 12, 1, 0),
};

Simple mixer control 'Headphone Jack Sense',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [on]

Simple mixer control 'Line Jack Sense',0
  Capabilities: pswitch pswitch-joined
  Playback channels: Mono
  Mono: Playback [on]

these two control only change JS MT2 and JSMT1

JS Mute Enable Selector

These three bits select and enable the jack sense muting action (see Table 41

try toogle to see any difference since FMUTE = Output is forced to mute independent of the respective volume register setting.