Comment 14 for bug 820092

refer to Intel Desktop Board D946GZIS Technical Product Specification

1.7 Audio Subsystem Product Description
The onboard audio subsystem consists of the following:
 • Intel 82801GB ICH7 • Analog Devices ADI1988A (or Sigmatel STAC9227) audio codec
 • Back panel audio connectors
 • Component-side audio headers
The audio subsystem supports the following features:
 • Advanced jack sense for the back panel audio jacks that enables the audio codec to recognize the device that is connected to an audio port. Within hardware constraints, the back panel audio jacks are capable of retasking according to the user’s definition, or can be automatically switched depending on the recognized device type.
  • Stereo input and output for all back panel jacks
 • Line out and Mic in functions for front panel audio jacks

if pin cap support impsense, this mean the driver may retask the rear mic jack automatically by measure the impedance since mic has higher impedance

Pincap 0x0000173f: IN OUT HP Detect Trigger ImpSense

refer to 9227 datasheet

3.2. 3.3. Impedance Sense
Impedance Sense is accomplished by on-chip circuitry that measures the impedance at the pin of the chip and compares it to internal reference impedance.
Below is a table that contains the bin information and codes returned when the pin widget impedance field in the Port Pin Sense widget is read.
Please note that even under the best conditions, there is no method to guarantee 100% impedance sensing due to variations in external circuitry and impedance overlap of devices that can be plugged into a jack.
The impedance sense table reflects both standard Line Out and Headphone output drivers.
Please reference the HD Audio Universal Jack Application Note on the SigmaTel Extranet for more information.

Table 1: Impedance Sense

Passive Speakers, Headset Speakers Impedance
Some Headset Speakers
Some Microphones
Microphones
Microphones
Amplified Speakers
Amplified Speakers,
Line In Amplified Speakers, Line In