[LinuxBIOS] LNXI Merge: lnxi-patch-14/16

Lu, Yinghai yinghai.lu at amd.com
Wed Sep 7 17:51:25 CEST 2005

>Are io-apics limited to apic ids 0x0-0x0f as well?
>My memory says to me the limit should be 0x0-0xff...

before enable ext_apic_id, Opteron only can use 4 bit for apic id, So only 16 apic id.

After enable ext_apic_id in every opteron, it will use 8 bit for apic id, So we got 256 apic id.

Then CPU can use 0x10 above apic id.

some io apic device only support 4 bit apic id, So We can leave 0x0-0xf to them.

that is for AMD, it is said that intel's from p4 has 256 for default.

I cut and paste something for you from Kernel list.

> - 1: 82489DX -- communication using a five-wire inter-APIC bus, 8-bit
>      physical ID, 32-bit logical ID, etc.,
> - 2: Pentium-style -- communication using a three-wire inter-APIC bus,
>      4-bit physical ID, 8-bit logical ID, etc.,
> - 3: P4-style -- communication using the system bus, 8-bit physical ID,
>      8-bit logical ID, etc.

>According to what AMD told us, all K8 CPUs support 8-bit APIC IDs
>("extended APIC IDs" in their speak), but they are only enabled
>"when both ApicExtId and ApicExtBrdCst in the HyperTransport Transaction
>Control Register are set".


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