[coreboot] KGPE-D16 / Problem booting with two CPUs

Timothy Pearson tpearson at raptorengineering.com
Wed Apr 11 21:30:02 CEST 2018

Hash: SHA1

This may be a general coreboot limitation at the moment.  The
compatibility sections for mixed CPUs in the BKDG are more concerned
with total power delivery and proper P-state setup than anything else.

If I recall correctly, coreboot assumes both CPUs have the same core
count when setting up APICs and such.  There are a number of places that
would need to be modified to remove this assumption; it's a leftover
from the original K8 code and would take some significant work to fix.
This also needs to be verified as I am going from memory here from a
couple of years ago.

On 04/11/2018 02:12 PM, Elisenda Cuadros wrote:
> Thank you for your reply Timothy.
> Vendor Bios doesn't print any special message regarding this.
> In fact it shows a total of 28 cores (16+12).
> I thought mixing CPUs from same families was supported.
> Regards,
> - Eli
> On 11/04/18 20:44, Timothy Pearson wrote:
>> I don't know if coreboot has support for differing CPUs in the same
>> mainboard; it's not something I can recall testing at any point.
>> The failure is occurring far before memory initialization, in CAR, in
>> core setup.  I'd guess it has something to do with the two CPUs you have
>> installed having different core counts.
>> Does the vendor BIOS print a message about the core count being limited
>> on one of the CPUs for compatibility reasons?
>> On 04/11/2018 12:57 PM, Elisenda Cuadros wrote:
>>> Hello,
>>> After testing the board for some weeks I bought another CPU (6276). I
>>> installed this into CPU1 slot and a 6238 in CPU2.
>>> I checked that both CPUs are shining and also the memory (Micron
>>> MT18JSF25672PDZ-1G4F1DD, populated in A2/C2/E2/G2 slots).
>>> The problem is that Coreboot seems to hang at the beginning. I attach
>>> console.log.
>>> I reinstalled all the devices twice, checked the vendor manual, docs in
>>> coreboot.org, messages in mailing list, but I don't know what is causing
>>> the problem.
>>> Last test I've done is booting with vendor bios, and it boots without
>>> problem.
>>> Any ideas?
>>> Thank you for your help.
>>> Regards,
>>> - Eli

- -- 
Timothy Pearson
Raptor Engineering
+1 (415) 727-8645 (direct line)
+1 (512) 690-0200 (switchboard)
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