Some parts of this documentation requires knowledge of the bridge and
related components that are not graphics related. These can be found
under the Intel -> Integrated chipsets section under the folder of
the same name.

The specific knowledge required is the amount of "stolen memory"
used by the graphics chipset (or even, if the integrated controller
is active at all). None of the registers documented here cover that,
you have to read that from the configuration space of the root PCI
device.