RE: IO-APIC on nforce2 [PATCH] + [PATCH] for nmi_debug=1 + [PATCH] for idle=C1halt, 2.6.5

[Allen Martin]

I'm happy to be able to make this information public to the Linux
community.  This information has been previously released to BIOS /
board vendors as an appnote, but in the interest of getting a workaround
into the hands of users the quickest we're making it public for possible
inclusion into the Linux kernel.


Problem:
C1 Halt Disconnect problem on nForce2 systems

Description:
A hang is caused when the CPU generates a very fast CONNECT/HALT cycle
sequence.

Workaround:
Set the SYSTEM_IDLE_TIMEOUT to 80 ns. This allows the state-machine and
timer to return to a proper state within 80 ns of the CONNECT and probe
appearing together.

Since the CPU will not issue another HALT within 80 ns of the initial
HALT, the failure condition is avoided.

This will require changing the value for register at bus:0 dev:0 func:0
offset 6c.

Chip   Current Value   New Value
C17       1F0FFF01     1F01FF01
C18D      9F0FFF01     9F01FF01

Northbridge chip version may be determined by reading the PCI revision
ID (offset 8) of the host bridge at bus:0 dev:0 func:0.  C1 or greater
is C18D.

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