[M] Change in coreboot[main]: drivers/intel/gma/opregion: Use CBFS cache to load VBT

[Nico Huber (Code Review)]

Attention is currently required from: Arthur Heymans, Eran Mitrani, Jakub Czapiga, Julius Werner, Jérémy Compostella, Kapil Porwal, Nick Vaccaro, Subrata Banik, Tarun.

Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/77886?usp=email )

Change subject: drivers/intel/gma/opregion: Use CBFS cache to load VBT
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Patch Set 32:

(2 comments)

File src/drivers/intel/gma/opregion.c:

https://review.coreboot.org/c/coreboot/+/77886/comment/3b5d45a5_b4bb8ad8 :
PS4, Line 27: cbfs_map
> > I did at line 36 in case of error. […]

IIRC, locate_vbt() is called rather early in ramstage. Doesn't this mean
we would lose a huge part of the cache if we don't unmap? IMO, it should
be part of this patch. Or is it a common practice to leak cache space?

File src/drivers/intel/gma/opregion.c:

https://review.coreboot.org/c/coreboot/+/77886/comment/116f4056_d17a5ad8 :
PS32, Line 48: 	data = NULL;
             : 	size = 0;
> can't we just `return NULL` from here ?

The `data = NULL;` would have to stay because it's static and used
to decide what to return in later calls.