broadwell mrc enables both igpu and dgpu to be enabled
at any given time. if the onboard (intel) gpu is set as
primary, the logic to disable it is not executed within
coreboot; instead, the igpu is used for vga decode.
on some t440p/w541 thinkpads, both an intel and nvidia
gpu are present. in this setup, the intel gpu must be
used for vga, and all output, but rendering can be
offloaded to the nvidia gpu (nvidia optimus).
optimus would never work on haswell mrc.bin, because it
always disables the igpu when a dgpu is present, so a hack
exists in coreboot that hides the dgpu from mrc, so that the
igpu remains enabled. broadwell mrc doesn't do this, so the
option to hide PEG devices has been disabled in these
configs.
the broadwell mrc has better peg device handling, and can
support 16gb modules on broadwell hardware; it may well
support these modules on haswell hardware too, though ddr3
sodimms are very hard to find (and expensive). (and currently
untested, with this patch)
Signed-off-by: Leah Rowe <leah@libreboot.org>
Leah Rowe