WM1811 buttons detection

[GR0S]

I looked into wm8994.c microphone detection code, it says it can detect up to 6 buttons.
But I can't find any impedance/resistance related code.

Here is detection listing

static void wm8958_button_det(struct snd_soc_codec *codec, u16 status)
{
struct wm8994_priv *wm8994 = snd_soc_codec_get_drvdata(codec);
int report;

report = 0;
if (status & 0x4)
report |= SND_JACK_BTN_0;

if (status & 0x8)
report |= SND_JACK_BTN_1;

if (status & 0x10)
report |= SND_JACK_BTN_2;

if (status & 0x20)
report |= SND_JACK_BTN_3;

if (status & 0x40)
report |= SND_JACK_BTN_4;

if (status & 0x80)
report |= SND_JACK_BTN_5;

snd_soc_jack_report(wm8994->micdet[0].jack, report,
wm8994->btn_mask);
}

Can anyone lookup into driver code?