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SubjectRe: [PATCH v3] sh: avoid using IRQ0 on SH3/4
Hi Rob,

On Mon, May 2, 2022 at 10:02 PM Rob Landley <rob@landley.net> wrote:
> Sounds like it's now outside of the IRQ range allocation, but I can't find where
> that's requested when registering the controller? (What is a "swizzle" anyway?)

PCI slots have 4 interrupts (#A, #B, #C, #D). In machines with
multiple slots, the interrupts lines are "swizzled", to avoid that all cards
using a single interrupt are mapped to the same host interrupt.

Typically, the mapping is:

host_irq = bus_irqs[(slot + irq_pin) % 4];

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds

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