__pci_read_base(9)

💅 __pci_read_base — read a PCI BAR, bestie

okay so this is a page from the Kernel API Manual (the 9 section, kernel internals zone ✨) and it's all about __pci_read_base. it's short, it's sweet, and it's literally the little guy that goes and reads a PCI BAR for you. let's get into it 🫶

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🌸 NAME 🌸

__pci_read_base — Read a PCI BAR 💖

like. that's the whole job. read the BAR. iconic behaviour honestly 👑

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✨ SYNOPSIS ✨

int __pci_read_base (struct pci_dev *dev , enum pci_bar_type type ,
       struct resource *res , unsigned int pos , u32 *sizes );

yes she takes five arguments, yes she returns an int, no we are not scared of her 💅

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🎀 ARGUMENTS 🎀

• dev — the PCI device. the main character of this whole situation 🦋
• type — type of the BAR. gotta know what flavour we're dealing with 🍓
• res — resource buffer to be filled in. she gets filled in, that's her whole arc ✨
• pos — BAR position in the config space. the address of where the magic happens 📍
• sizes — array of one or more pre-read BAR masks. plural! array! no cap 🙈

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💜 DESCRIPTION 💜

Returns 1 if the BAR is 64-bit, or 0 if 32-bit.

that's it. that's the description. one line and she ATE 🔥 like honestly the whole function is a vibe check on how wide your BAR is and then it tells you with a 1 or a 0, bestie. maths is mathing 😭

ngl the manpage really just says this and dips. short queen energy 💀

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🌈 SEE ALSO 🌈

the kernel file ./drivers/pci/probe.c is where all this lives, and these are the siblings/friends-of-the-family you should also go look at:

• __pci_size_bars(9)
• pcie_get_link_speed(9)
• pci_ea_fixed_busnrs(9)
• pci_ext_cfg_is_aliased(9)
• pci_cfg_space_size_ext(9)
• pci_intx_mask_broken(9)
• pci_setup_device(9)
• pcie_relaxed_ordering_enabled(9)
• pci_release_dev(9)
• pci_scan_slot(9)
• pci_scan_child_bus_extend(9)
• pci_scan_child_bus(9)
• pcibios_root_bridge_prepare(9)
• pci_rescan_bus_bridge_resize(9)
• pci_rescan_bus(9)

that's a whole friend group and every single one of them is invited to the group chat 💅✨

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and that's the page!! this one came out of ./drivers/pci with a date stamp of October 2026, filed under __pci_read_base(9) in the Kernel API Manual. go read a BAR, bestie, you've got this 🫶💖🎀