STRUCT MPIC(9)

💖 struct mpic(9) — the MPIC private data structure, bestie 💖

okay so this is a page from the Kernel API Manual, and it's literally all about struct mpic — the MPIC private data structure. yes, the actual struct, the whole thing, every single member, no gatekeeping here 🫶

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✨ NAME ✨

struct mpic — the MPIC private data structure. that's it, that's the vibe 💅

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🌸 SYNOPSIS 🌸

here's the whole struct, character for character, do not touch, do not "clean it up", just read it:

struct mpic {
    void __iomem *base;
    void __iomem *per_cpu;
    int parent_irq;
    struct irq_domain *domain;
  #ifdef CONFIG_SMP;
    struct irq_domain *ipi_domain;
  #endif;
  #ifdef CONFIG_PCI_MSI;
    struct irq_domain *msi_inner_domain;
    unsigned long msi_used[BITS_TO_LONGS( PCI_MSI_FULL_DOORBELL_NR)];
    struct mutex msi_lock;
    phys_addr_t msi_doorbell_addr;
    u32 msi_doorbell_mask;
    unsigned int msi_doorbell_start, msi_doorbell_size;
  #endif;
    u32 doorbell_mask;
 };

like, notice the #ifdef CONFIG_SMP; and #ifdef CONFIG_PCI_MSI; with the trailing semicolons?? iconic, slightly cursed, but we're not changing it. periodt.

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🎀 Members 🎀

okay bestie, member-by-member tour, let's go 🦋

• base — MPIC registers base address. the home base, the main character energy ✨
• per_cpu — per-CPU registers base address. one for every CPU, because sharing is not always caring 💜
• parent_irq — parent IRQ if MPIC is not top-level interrupt controller. like, if MPIC isn't the boss of the interrupt chain, this is who it answers to 👑
• domain — MPIC main interrupt domain. the big one, the main domain 💅
• ipi_domain — IPI domain. (this one lives inside #ifdef CONFIG_SMP, iykyk)
• msi_inner_domain — MSI inner domain. the domain inside the domain 🌀
• msi_used — bitmap of used MSI numbers. lowkey a whole tracking system for who's taken 🌈
• msi_lock — mutex serializing access to msi_used. no chaos allowed, only one at a time 🔒
• msi_doorbell_addr — physical address of MSI doorbell register. ring ring, it's an interrupt 💀
• msi_doorbell_mask — mask of available doorbell bits for MSIs. and bestie, it's either PCI_MSI_DOORBELL_MASK or PCI_MSI_FULL_DOORBELL_MASK, no in-between 🎯
• msi_doorbell_start — first set bit in msi_doorbell_mask. first out the door, fr fr ⭐
• msi_doorbell_size — number of set bits in msi_doorbell_mask. count 'em up 🔥
• doorbell_mask — doorbell mask of MSIs and IPIs, stored on suspend, restored on resume. like a little nap that saves state, obsessed 😭

real talk: the msi_inner_domain through msi_doorbell_size crew only exist under #ifdef CONFIG_PCI_MSI, and ipi_domain only under #ifdef CONFIG_SMP. and doorbell_mask sits outside both, always present, always thriving 🙈

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🧚 SEE ALSO 🧚

• Kernel file ./drivers/irqchip/irq-armada-370-xp.c — go read it, tell me everything 💖

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okay and finally, the cute sign-off: this little masterpiece comes to you from ./drivers/irqchip, dated October 2026. slay, go configure your interrupts responsibly 🌸🎀🦋