Problems with irq mapping in qemu v5.2

[Guenter Roeck <linux@roeck-us.net>]

Hi,

commit 459ca8bfa41 ("pci: Assert irqnum is between 0 and bus->nirqs in
pci_bus_change_irq_level") added sanity checks to the interrupt number passed
to pci_bus_change_irq_level(). That makes sense, given that bus->irq_count
is indexed and sized by the number of interrupts.

However, as it turns out, the interrupt number passed to this function
is the _mapped_ interrupt number. The result in assertion failures for various
emulations.

Examples (I don't know if there are others):

- ppc4xx_pci_map_irq() maps the interrupt number to "slot - 1". Obviously
  that isn't a good thing to do for slot 0, and indeed results in an
  assertion as soon as slot 0 is initialized (presumably that is the root
  bridge). Changing the mapping to "slot" doesn't help because valid slots
  are 0..4, and only four interrupts are allocated.
- pci_bonito_map_irq() changes the mapping all over the place. Whatever
  it does, it returns numbers starting with 32 for slots 5..12. With
  a total number of 32 interrupts, this again results in an assertion
  failure.

ppc4xx_pci_map_irq() is definitely buggy. I just don't know what the
correct mapping should be. slot  & 3, maybe ?

I don't really have a good solution for pci_bonito_map_irq(). It may not
matter much - I have not been able to boot fuloong_2e since qemu v4.0,
and afaics that is the only platform using it. Maybe it is just completely
broken ?

Thanks,
Guenter