Early cbmem implementation

Early CBMEM support

By the 4.7 release (October) support for cbmem in romstage is required for all platforms. Original message from mailing list can be found there

Following mail gives some insight on what needs to be done to satisfy the romstage cbmem requirement.

Essential extract from above message:

> In preparation to remove the static CBMEM allocator, tag the chipsets
> that still do not implement get_top_of_ram() for romstage.

So you need to implement that function for your chipset, remove the
Kconfig selection, and if I remember correctly, everything else should
then start working nicely.

The next step is then to also add time-stamps to CBMEM, that can be read out with cbmem -t.

It looks that implementation in northbridge is necessary. For apu2 it will be in src/northbridge/amd/pi/00730F01.

Few more useful links below:

• Chipsets that are marked as missing EARLY_CBMEM implementation

• One example of Intel chipset implementation

• Another example of Intel chipset implementation

There is much work already done by Kyosti Malkki for AGESA here I recommend to look at related topics too.

This can be an inspiring source AGESA: Add romstage timestamps

I also advise to contact Kyosti and ask about the progress of his work. Maybe there is something we could do to help.