prepopulate_bars(9)

okay bestie, welcome to prepopulate_bars(9) from the Kernel API Manual — the page where we fill in BARs with defaults, and honestly it’s giving “make the PCI core happy” energy 💅✨

💖 NAME 💖

prepopulate_bars - Fill in BARs with defaults 🌸

✨ SYNOPSIS ✨

void prepopulate_bars (struct hv_pcibus_device *hbus );

🎀 ARGUMENTS 🎀

• hbus — Root PCI bus, as understood by this driver 🫶

🌸 DESCRIPTION 🌸

okay so here’s the vibe: the core PCI driver code seems much, much happier if the BARs for a device have values upon first scan. So we fill them in. no cap, that’s the assignment 💜

The algorithm below works down from large sizes to small, attempting to pack the assignments optimally — it’s lowkey doing a little packing puzzle 🧩✨

And here’s the assumption, enforced in other parts of the code: the beginning of the memory-mapped I/O space will be aligned on the largest BAR size. periodt. Don’t forget it, bestie 💅

🦋 SEE ALSO 🦋

Kernel file: ./drivers/pci/controller/pci-hyperv.c — here’s the whole friend group, iykyk:

• struct hv_msi_desc(9)
• struct hv_msi_desc2(9)
• struct tran_int_desc(9)
• hv_irq_retarget_interrupt(9)
• hv_pci_generic_compl(9)
• devfn_to_wslot(9)
• wslot_to_devfn(9)
• _hv_pcifront_read_config(9)
• _hv_pcifront_write_config(9)
• hv_pcifront_read_config(9)
• hv_pcifront_write_config(9)
• hv_pci_read_config_compl(9)
• hv_read_config_block(9)
• hv_pci_write_config_compl(9)
• hv_write_config_block(9)
• hv_register_block_invalidate(9)
• hv_msi_free(9)
• hv_compose_msi_msg(9)
• hv_pcie_init_irq_domain(9)
• get_bar_size(9)
• survey_child_resources(9)
• create_root_hv_pci_bus(9)
• q_resource_requirements(9)
• new_pcichild_device(9)
• get_pcichild_wslot(9)
• pci_devices_present_work(9)
• hv_pci_start_relations_work(9)
• hv_pci_devices_present(9)
• hv_pci_devices_present2(9)
• hv_eject_device_work(9)
• hv_pci_eject_device(9)
• hv_pci_onchannelcallback(9)
• hv_pci_protocol_negotiation(9)
• hv_pci_free_bridge_windows(9)
• hv_pci_allocate_bridge_windows(9)
• hv_allocate_config_window(9)
• hv_pci_enter_d0(9)
• hv_pci_query_relations(9)
• hv_send_resources_allocated(9)
• hv_send_resources_released(9)
• hv_pci_probe(9)
• hv_pci_remove(9)

💅 final sign-off: this page’s source/version is ./drivers/pci/controller, the date is October 2026, and the manual page is prepopulate_bars(9). bye bestie, go fill those BARs 🫶✨