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MRC caches in a certain way, that Heads was able to work
around in their build system, for this board.
I've adapted the relevant config differences, from their project
as of heads revision 96440b928acb06de5b925ea12014c9c280b23165
The downside is that CBFS now has to be 8MB in size. The upside
is that the machine also boots much faster
See:
https://github.com/osresearch/heads/pull/1282/commits/f0792117efa177ded19878f652c5a28e8cc62a71
https://github.com/osresearch/heads/pull/1282#issuecomment-1400634600
I have not adapted their IFD changes, versus Libreboot, because theirs
simply has a different version string, and uses different read/write
permission bits for regions as defined in the IFD.
This affects:
t440p_12mb_mrc
w541_12mb_mrc
S3 suspend/resume still broken on these targets which use the libre
MRC init (replacement code by Angel Pons, recently merged in lbmk):
t440p_12mb
w541_12mb
With clever use of FMAP, the rest of the BIOS region might still be
used. However, for our purposes, 8MB CBFS will do just fine.
Heads's changes configure MRC so that caching is handled properly,
for when the machine returns from sleep. Setting CBFS to be any
higher will result in slower boot times, and broken S3 resume, due
to MRC cache misalignment (this is based on my understanding, reading
through the Heads project looking at their research on this).
At some point in the future, Angel's libre MRC code will probably
be finished, and merged, with more fine tuning possible to allow
bigger CBFS sizes.
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