[coreboot] [RFC] Getting CAR to work on P6 family; Port SECC P6 L2 cache initialization code to where?

[Keith Hui]

Hi all, this is a RFC.

While Joseph, Idwer and myself convened on IRC for the past two days
trying to get CAR working on the P6 family of CPUs, we found that -

The Intel CAR code works as is on Tualatin cores, L2 cache fully enabled
The same code works for me on a Katmai, but only L1 cache is enabled
This code does not boot at all for Idwer who also has a Katmai, and
has stumped everyone
We need to port a piece of long code from coreboot v1 that initializes
the off-chip L2 cache found on Klamath/Deschutes/Katmai CPUs.
They are respectively models 63x,65x and 67x.
16k of L1 is enough. We're only using 4k for CAR on Intel.

It was written in C. I looked at the OEM BIOS for P2B-LS and L2 is
initialized from the "inner BIOS", like the RAM stage of coreboot,
when RAM is fully up and running. This means this can go into
model_6xx_init(), which is prefereable as I just need to make enough
adjustments to make it work again.

Joseph OTOH suggests that I should port this code into
cache_as_ram.inc which is much earlier, actually before motherboard
romstage. This code is assembly, meaning I'll need to port this thing
back to assembly.

Question is: Where should I port this code to? CPU driver, or cache_as_ram.inc?

A patch to separate model 67x from model 6xx will soon come, either
from me or Joseph. A similar one could be done for 65x and 63x. I do
not have 66x Celerons to test so I cannot ascertain if this special
attention will be needed for them.

Thanks
Keith