Comment 155 for bug 1838373

I looked further into the docs regarding multiplexing, specifically...

Table 3-52.Northwest Community Mapping (TXE and Direct IRQ), important to see the note below the table:
https://www.intel.com/content/dam/www/public/us/en/documents/product-briefs/silver-celeron-datasheet-vol-1.pdf

9.365 Event Trigger Output Enable (EVOUTEN_0)—Offset 210h
29.367 Event Trigger Mapping (EVMAP_0)—Offset 220h
https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/silver-celeron-datasheet-vol-2.pdf

And found a similar-sounding EFI implementation for broxton in

https://github.com/tianocore-training/PlatformBuildLab_UP2_FW/blob/7600efc681e74d08682ef32ce8c3f0230721233b/FW/PlatformBuildLab/MV3/edk2-platforms/Silicon/BroxtonSoC/BroxtonSiPkg/Library/GpioLib/GpioLib.c#L308

It could be that i915 is wreaking havoc on the registers involved which are already properly set by EFI.