Microphone / Headphones combo port does not work in BootCamp
Solution 1:
Not sure if people are still having a problem with this as it's been almost a year, but I was running into this problem with my Mac mini 2014 with Windows 10 Home and Bootcamp v6.0. The sound card is Cirrus Logic CS4208 (AB 108), and I couldn't get Windows to recognize the mic on my headset which was designed for iPhone/Apple usage.
After not being able to find the driver for the CS4208 (AB 108) at a legitimate site on the net (results almost always required a 3rd party driver downloader - no thanks!), I went to Cirrus Logic's website and tried to search for another driver. I was able to find CS4207 from their website, downloaded the zip file, and tried to update the CS4208 driver with files on this zip. The driver was taken, and, after a restart, the microphone now showed up (even though it was still showing CS4208 AB 108). It works!
I even rolled back the driver and updated again to confirm it works, and it sure does! I also have another 2016 MBP that I would like to test. Will update here after.
Here's a few screenshots before the driver update to CS4207:
And after updating the drivers and restart:
Solution 2:
This worked for me. It was a Windows privacy issue: https://www.youtube.com/watch?v=ZssiZtyKaNk
You can test by recording your voice with the Voice Recorder Application. Give it permissions from Settings > Privacy Settings > Microphone. Also make sure Windows has permissions to use the microphone.
Solution 3:
If people are still having this issue in 2019 and have USB-C ports on their Mac, Apple's USB-C to 3.5mm adapter seems to fix this issue. While it doesn't work on macOS, it certainly allow you to use the microphone on Apple Earpods (and the in-line controls) and other headsets. The adapter is $9 in US and is mainly for iPad Pro 2018. I hope this helps, as it works perfectly for me!
Or if you have an Xbox one controller with a 3.5mm jack (I'm not sure about ps4 controllers) you can use that as a USB sound card
Solution 4:
According to https://discussions.apple.com/thread/6767136 this is currently not possible. If someone does get it to work I will happily award a bounty to an answer describing how to do it.
Solution 5:
It appears that Windows 10 running the latest Bootcamp does recognize the TRRS microphone now:
Hi there. I've been monitoring and looking for a solution for this for sometime and it seems the latest version of bootcamp released today (Bootcamp 6.0) with Windows 10 fixes the problem.
I had Windows 10 installed through bootcamp and updated to bootcamp 6 today (Aug 13). Surprisingly, I plugged in my iPhone headset (which is TRRS) and noticed windows installing some drivers. ...
Headset is working just like it does in OSX now, awesome for VOIP or gaming. Very happy camper here!
Should note that I am running Windows 10 with Bootcamp 6 on a late 2013 Retina Macbook Pro.