On Fri, Feb 13 2004, Sy, Dely L wrote:
> Since filling out the INTERRUPT_LINE is needed for systems running
> with legacy irqs and not needed for systems running with IO-APIC.  The

> possible
> solutions:
> 1) Best is there is a run-time check (a flag or an API call) that tells
>    whether the system is running on legacy mode or IO-APIC mode. Is there
>    such check that you know of?

Dan suggested that we look at what IRQ the hotplug controller has been
assigned in the MPS table. If its < 0x10 we're in legacy/mapped mode.
That would probaly work

> > >
> > > Do those servers work on 2.6.2 without my patch?
> > >
>
> > Yes
>
> They work but they get dev->irq = 9 or 11 in the APIC enabled mode.
> Correct?
>

Yes. All hot-added adapters get legacy IRQs like IRQ5 in the example
below where eth2 was added after bootup:


linux:~ # cat /proc/interrupts
           CPU0       CPU1       CPU2       CPU3
0:     831113          0          0          0    IO-APIC-edge  timer
1:        255          0          0          0    IO-APIC-edge  i8042
2:          0          0          0          0          XT-PIC  cascade
5:          0          0          0          0          XT-PIC  eth2
8:          2          0          0          0    IO-APIC-edge  rtc
12:         92          0          0          0   IO-APIC-edge  i8042
14:         29          0          0          0   IO-APIC-edge  ide0
20:          0          0          0          0   IO-APIC-level cciss0
21:          0          0          0          0   IO-APIC-level cciss1
29:        107          0          0          0   IO-APIC-level eth0
30:       7702          0          0          0   IO-APIC-level aic7xxx
31:         30          0          0          0   IO-APIC-level aic7xxx
34:        336          0          0          0   IO-APIC-level
cpqphp.o, cpqphp.o
NMI:          0          0          0          0
LOC:     830760     830893     830892     830891
ERR:          0
MIS:          0

I attached a patch that does the legacy mode check that Dan suggested
and IRQs for hot-added adapters seems to be given out in the APIC range.