pci_swizzle_interrupt_pin(9)

📦 version 7.3.1, in nixpkgs unstable

💅 pci_swizzle_interrupt_pin — from the Kernel API Manual, bestie ✨

Okay so picture this: it's pci_swizzle_interrupt_pin(9), it lives in the Kernel API Manual, and it's here to do exactly one iconic little thing — swizzle INTx for a device behind a bridge. That's the whole vibe. Let's get into it 🫶

✨ SYNOPSIS ✨

u8 pci_swizzle_interrupt_pin (const struct pci_dev *dev , u8 pin );

🎀 ARGUMENTS 🎀

  • dev — the PCI device, fr. This is your main character here 💖
  • pin — the INTx pin, and the mapping is not mysterious, bestie, it's literally this: 1=INTA, 2=INTB, 3=INTC, 4=INTD. Memorize it, it's giving flashcards 🌸

🔥 DESCRIPTION 🔥

So what does it actually do? It performs INTx swizzling for a device that's sitting behind one level of bridge. One. Level. Don't get cute with it 💅

And this isn't just a fun idea someone had — it's required by section 9.1 of the PCI-to-PCI bridge specification for devices behind bridges on add-in cards. So yeah, spec-mandated behavior, no cap 👑

Now here's the little plot twist: for devices with ARI enabled, the slot number is always 0. That's per the Implementation Note in section 2.2.8.1 of the PCI Express Base Specification, Revision 2.1. Write that down 📝

Lowkey the whole function is just "fix the pin number so the interrupt actually lands where it should." Small function, big slay ✨

🦋 SEE ALSO 🦋

Kernel file ./drivers/pci/irq.c, and also these besties:

And that's the page, gorgeous 🌈 — brought to you from the ./drivers/pci directory, dated October 2026, under the header pci_swizzle_interrupt_pin(9) in the Kernel API Manual. Go swizzle responsibly, mwah 💜🧚

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