RE: [(repost) git Patch 1/1] avoid IRQ0 ioapic pin collision

[Brown, Len]

<6>IOAPIC[64]: apic_id 127, version 32, address 0xfec49000, GSI
1728-1751

wow, big box!

>I have tested this algorithm and it worked just fine for me... I used
>the following compression code in mp_register_gsi():
>
>
>int     irqs_used = 0;
>int     gsi_to_irq[NR_IRQS] = { [0 ... NR_IRQS-1] = -1 };
>...
>
>        if (triggering == ACPI_LEVEL_SENSITIVE) {
>                if (gsi > NR_IRQS) {
>                        int i;
>                        printk("NBP: looking for unused IRQ\n");
>                        for (i = nr_ioapic_registers[0]; i < NR_IRQS;
i++) {
>                                if (gsi_to_irq[i] == -1) {
>                                        gsi_to_irq[i] = gsi;
>                                        gsi = i;
>                                        break;
>                                }
>                        }
>                        if (i >= NR_IRQS) {
>                                printk(KERN_ERR "GSI %u is too high\n",
...
>                                return gsi;
>                        }
>                } else
>                        gsi_to_irq[gsi] = gsi;
>        }

the problem with this code as it stands is that acpi/mp_register_gsi()
can be called with gsi in any order.  So it is possible
for the compression code above to select gsi_to_irq[n]
and later for the non-compression path to over-write gsi_to_irq[n].

Also, I would prefer that this code be in ioapic_renumber_irq(), as I
think
it is unnecessarily complex to re-number, and then re-number again.
(gsi_irq_sharing() is a separate discussion)

I think this should be model-specific, but if you feel that handling
(gsi > NR_IRQS) here is important in the generic case, then I'm
fine with this being a default ioapic_renumber_irq() handler
that a platform can augment/override.

Re: returning error
At one point acpi_register_gsi() was able to return an error.
However, that was broken when acpi_gsi_to_irq() was created,
and then broken worse when that routine was modified
with gsi_irq_sharing().  if you BUG() on i > NR_IRQS,
that would be consistent wth gsi_irq_sharing().

thanks,
-Len
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