Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/35100 )
Change subject: mb/asrock/h110m: add missing pci devices to tree ......................................................................
Patch Set 9: Code-Review+2
(1 comment)
https://review.coreboot.org/c/coreboot/+/35100/3/src/mainboard/asrock/h110m/... File src/mainboard/asrock/h110m/devicetree.cb:
https://review.coreboot.org/c/coreboot/+/35100/3/src/mainboard/asrock/h110m/... PS3, Line 277: d
This device will be enabled after initialization in the FSP, regardless of the settings in the devic […]
Disabling it on the devicetree should be enough, I guess.
In any case, you should be able to disable the Gaussian Mixture Model (GMM) using the "GmmEnable" UPD on FSP-S. Note that the UPD name never referenced in coreboot code, but it appears here:
3rdparty/fsp/KabylakeFspBinPkg/Include/FspsUpd.h
AmberLake also has that UPD, but Cannonlake and Coffelake renamed it to "GnaEnable".
I never tried using the DEVEN register. Feel free to experiment :)