Hi William, hello everyone,
The MP_valid_apicid() function [arch/i386/kernel/mpparse.c] checks
whether the APIC version field is >=20 in order to determine whether the
CPU supports 8-bit physical APIC ids.
We currently have two modern processors oin our labs (Intel Xeon MP, AMD
Dual-Core Opteron 875) for which this test is wrong because their APIC
ids are both 16, but they _do_ support 8-bit APIC ids. This leads to
erratic error messages and to valid CPUs not being detected.
Unfortunately I cannot tell why this is so, and what test should be used
instead to make sure a CPU supports 8-bit APIC IDs.
The AMD BIOS and kernel developer's guide for Athlon64 and Opteron
processors says
"When both ApicExtId and ApicExtBrdCst in the HyperTransport"
Transaction Control Register are set, all 8 bits of APIC ID are used."
This refers to the TCR register. Reading that would require PCI
configuration space access before the APICs are set up, I don't know if
that's possible.
(http://www.amd.com/us-en/assets/content_type/white_papers_and_tech_docs/26094.PDF)
The Intel Manual simply says
"For the Pentium 4 and Intel Xeon Processors, the xAPIC specification
extends the local APIC field to 8 bits". The CPUs we have are Xeon MP
(family 15, model 4); their local APIC version is 16, and they do
support 8-bit APIC-IDs.
I guess it's up to the Intel an AMD people to have a final word on this,
but the current implementation is clearly wrong for these latest CPU types.
Regards
Martin
--
Martin Wilck Phone: +49 5251 8 15113
Fujitsu Siemens Computers Fax: +49 5251 8 20409
Heinz-Nixdorf-Ring 1 mailto:[email protected]
D-33106 Paderborn http://www.fujitsu-siemens.com/primergy
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