STRUCT PCI_EPF_DOORBELL_MSG(9)

💖 struct pci_epf_doorbell_msg(9) — the kernel API manual, bestie edition 💖

okay so this is a page from the Kernel API Manual, and today's main character is struct pci_epf_doorbell_msg. yes it's a struct, yes it's about doorbells (the interrupt kind, not the Ring kind 🔔), and yes we're gonna get into it.

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✨ NAME ✨

struct pci_epf_doorbell_msg — literally just represents a doorbell message. that's the whole vibe. 🛎️

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🌸 SYNOPSIS 🌸

here's the shape of it, bestie, copy it exactly:

struct pci_epf_doorbell_msg {
    struct msi_msg msg;
    int virq;
    unsigned long irq_flags;
    enum pci_epf_doorbell_type type;
    enum pci_barno bar;
    resource_size_t offset;
    dma_addr_t iova_base;
    size_t iova_size;
 };

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🎀 Members 🎀

bestie. sit down. we're doing a member-by-member breakdown and it's giving thorough. 💅

• msg — the doorbell address/data pair that gets mapped into BAR space. so like, for MSI-backed doorbells this is the MSI message, but for "embedded" doorbells it's actually an MMIO write that asserts an interrupt on the EP side. two vibes, one field. 🦋
• virq — the IRQ number of this doorbell message. that's it, that's the field. ✨
• irq_flags — the flags you need for request_irq/request_threaded_irq. callers are allowed to OR-in extra flags on top (e.g. IRQF_ONESHOT) — very generous of them ngl. 🔥
• type — the doorbell type. yep. 🎀
• bar — the BAR number where the doorbell target is already exposed to the RC. if it's not exposed, it's NO_BAR. keep that in mind okay. 👑
• offset — the offset within bar for the doorbell target. ⚠️ this one is only valid iff bar != NO_BAR ⚠️ — so don't come for me if you read it when it's NO_BAR, that's on you. 😭
• iova_base — Internal: the base DMA address that dma_map_resource returned for the embedded doorbell MMIO window. it's used only for unmapping, so don't get any ideas. valid when type is PCI_EPF_DOORBELL_EMBEDDED and iova_size is non-zero. 🧚
• iova_size — Internal: the size of the dma_map_resource mapping at iova_base. it's zero when no mapping was created (e.g. a pre-exposed fixed BAR). zero = no mapping, no cap. 💀

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🌈 SEE ALSO 🌈

go touch grass in the kernel source, specifically:

Kernel file ./include/linux/pci-epf.h

and then these absolute icons:

struct pci_epf_header(9), struct pci_epf_ops(9), struct pci_epc_event_ops(9), struct pci_epf_driver(9), struct pci_epf_bar_submap(9), struct pci_epf_bar(9), struct pci_epf(9), struct pci_epf_msix_tbl(9)

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fr fr read the whole friend group, they all connect. iykyk 🫶

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okay that's the page!! 🎉 source is ./include/linux, dated October 2026, and the page itself is struct pci_epf_doorbell_msg(9) — slay, goodbye, go map some doorbells responsibly 💜⭐🌸