ICH5 irq fails in 100% native mode

[Con Kolivas]

While recently setting up a new machine with 2.6.3 and then 2.6.7-rc2 I
discovered this over and over again causing system stalls:

disabling IRQ18

syslog showed:

Jun  2 00:31:28 localhost kernel: irq 18: nobody cared!
Jun  2 00:31:28 localhost kernel:  [__report_bad_irq+42/121] 
[note_interrupt+145/175]  [do_IRQ+279/321]  [common_interrupt+24/32] 
[__do_softirq+66/177]
[do_softirq+45/47]  [do_IRQ+286/321]  [common_interrupt+24/32] 
[default_idle+0/44]  [default_idle+41/44]  [cpu_idle+46/60] 
[start_kernel+407/467]  [unkno
wn_bootoption+0/294]

dmesg revealed this:
ICH5: 100%% native mode on irq 18

Adding "noapic" to boot options simply moved the error to IRQ5 and occurred
routinely during boot at the ICH5 definition.


A quick google revealed the IDE settings in BIOS might be related so I disabled
the "ENHANCED" option for the ide controller which is both P-ATA and S-ATA and
chose the "COMPATIBLE" option.

The error went away, and now dmesg shows this:

ICH5: not 100%% native mode: will probe irqs later


While I am not able to determine whether there is any performance penalty for
this it seems that the probing of irqs at this point is responsible.

The hardware is an ASUS P4P800S motherboard with i848 chipset + ICH5 and a 2.8C
P4HT.

While this is a workaround I wonder what I/we need to do to make it work in
native mode.

Advice?

Con
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