pci_msi_vec_count(9)

✨ pci_msi_vec_count(9) — from the Kernel API Manual, bestie ✨

Okay so picture this: you're deep in ./drivers/pci/msi and you just need to know how many MSI vectors a device can send. That's literally this function. It's the kernel API manual entry for pci_msi_vec_count, and it's kind of a whole vibe. Let's get into it 💅

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🌸 NAME 🌸

pci_msi_vec_count — returns the number of MSI vectors a device can send. That's the whole job. No cap, that's it.

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🦋 SYNOPSIS 🦋

int pci_msi_vec_count (struct pci_dev *dev );

Yes bestie, that's the signature, copied exactly, don't come for me 🙈

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🎀 ARGUMENTS 🎀

• dev — the device you're reporting about. It's giving "main character" — everyone's asking about this one.

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💖 DESCRIPTION 💖

So here's the tea 🍓: this function returns the number of MSI vectors a device requested via the Multiple Message Capable register. Slay.

But listen — if the device is not capable of sending MSI interrupts, it comes back with a negative errno. Sad girl hours, lowkey 😭

Otherwise? The call succeeds and returns a power of two, up to a maximum of 2^5 (32), according to the MSI specification. So like, 32 is the ceiling, bestie, don't ask for more, it's not happening 🔥

Ngl, the power-of-two thing is not a suggestion — it's the spec. It's giving "rules are rules" 👑

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👑 SEE ALSO 👑

• Kernel file ./drivers/pci/msi/msi.c
• pci_msi_supported(9)
• pci_msi_mask_irq(9)
• pci_msi_unmask_irq(9)
• msi_capability_init(9)
• msix_prepare_msi_desc(9)
• msix_capability_init(9)
• pci_msix_write_tph_tag(9)

Go read them, they're iconic too, iykyk 🫶

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And that's the page, bestie ✨ Sourced from ./drivers/pci/msi, dated October 2026, and yes the header on this one is literally pci_msi_vec_count(9). Periodt 💜🦋