[coreboot] FSP settings according to decode-dimms

[Nico Huber]

Hi Zvi,

I assume you still ask for the BayTrail FSP, correct? You didn't
mention it in your last mails.

On 11/10/18 8:47 AM, Zvi Vered wrote:
> Module Type                                     72b-SO-UDIMM

This suggests that you have a DIMM? i.e. a module, not soldered down
DRAM, is that correct?

> Enable Memory Down: Disabled
> DRAM Speed: 1333
> ...

These settings all live in a struct called MEMORY_DOWN_DATA. I don't
know for sure, but I assume with "EnableMemoryDown Disabled" you disable
the whole struct. I can also not find a single board in coreboot that
sets `EnableMemoryDown` explicitly to 0.

Maybe one of the FSP BayTrail maintainers can clarify? or even provide
some documentation?

Also, please use coreboot's infrastructure to set these things from your
mainboard's `romstage.c` or `devicetree.cb`. If you want help with BCT,
better ask Intel.

If you have a real DIMM module with an SPD that can be read from SMBus,
I would try setting `PcdMrcInitSPDAddr1`. Be aware that it expects the
SMBus address shifted left by 1 (e.g. the 7-bit address 0x50 would be
0xa0 for FSP). You can set it from the devicetree, for examples check
the source, e.g.:
  git grep '"PcdMrcInitSPDAddr1"'

If you don't have a module but soldered down memory, here's an example
how to map the values from your SPD to FSP: `mainboard/siemens/mc_tcu3/
romstage.c`.

I'm not sure if this works though, as this board also sets
`PcdMrcInitSPDAddr*` in the devicetree, which confuses me (same for
intel/minnowmax, Intel maintainers?).

Hope that helps,
Nico