usb4_switch_map_pcie_down(9)

💅 usb4_switch_map_pcie_down — Kernel API Manual ✨

okay so bestie, the manual name is usb4_switch_map_pcie_down(9) and honestly? iconic little helper. let's get into it 🫶

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🌸 NAME 🌸

usb4_switch_map_pcie_down — map a USB4 port to a PCIe downstream adapter. that's it, that's the job 💖

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✨ SYNOPSIS ✨

struct tb_port * usb4_switch_map_pcie_down (struct tb_switch *sw , const
       struct tb_port *port );

look at that signature. it's giving "give me two things and i'll give you a pointer" 🔥

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🎀 ARGUMENTS 🎀

• sw — the USB4 router. your main character struct, literally.
• port — the USB4 port. the one we're trying to place on the map 🗺️

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💜 DESCRIPTION 💜

so here's the vibe: USB4 routers have a direct mapping between USB4 ports and PCIe downstream adapters — that's exactly the spot where the PCIe topology gets extended. no cap.

what this function does is simple and slay: hand it a sw and a port, and it returns the corresponding downstream PCIe adapter for you. and if no such mapping was possible? it gives you NULL. not everything works out, and that's okay bestie 😭

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⭐ RETURN ⭐

pointer to struct tb_port — or NULL if it wasn't found. that's the whole deal 💅

heads up: NULL here is a real, legit answer, not an error vibe. check it before you deref, fr fr 🙈

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🦋 SEE ALSO 🦋

kernel file ./drivers/thunderbolt/usb4.c, plus the whole friend group 💖

usb4_switch_check_wakes(9), usb4_switch_setup(9), usb4_switch_configuration_valid(9), usb4_switch_read_uid(9), usb4_switch_drom_read(9), usb4_switch_lane_bonding_possible(9), usb4_switch_set_wake(9), usb4_switch_set_sleep(9), usb4_switch_nvm_sector_size(9), usb4_switch_nvm_read(9), usb4_switch_nvm_set_offset(9), usb4_switch_nvm_write(9), usb4_switch_nvm_authenticate(9), usb4_switch_nvm_authenticate_status(9), usb4_switch_credits_init(9), usb4_switch_query_dp_resource(9), usb4_switch_alloc_dp_resource(9), usb4_switch_dealloc_dp_resource(9), usb4_port_index(9), usb4_switch_map_usb3_down(9), usb4_switch_add_ports(9), usb4_switch_remove_ports(9), usb4_port_unlock(9), usb4_port_hotplug_enable(9), usb4_port_reset(9), usb4_port_configure(9), usb4_port_unconfigure(9), usb4_port_configure_xdomain(9), usb4_port_unconfigure_xdomain(9), usb4_port_sb_read(9), usb4_port_sb_write(9), usb4_port_router_offline(9), usb4_port_router_online(9), usb4_port_enumerate_retimers(9), usb4_port_clx_supported(9), usb4_port_asym_supported(9), usb4_port_asym_set_link_width(9), usb4_port_asym_start(9), usb4_port_margining_caps(9), usb4_port_hw_margin(9), usb4_port_sw_margin(9), usb4_port_sw_margin_errors(9), usb4_port_retimer_set_inbound_sbtx(9), usb4_port_retimer_unset_inbound_sbtx(9), usb4_port_retimer_is_last(9), usb4_port_retimer_is_cable(9), usb4_port_retimer_nvm_sector_size(9), usb4_port_retimer_nvm_set_offset(9), usb4_port_retimer_nvm_write(9), usb4_port_retimer_nvm_authenticate(9), usb4_port_retimer_nvm_authenticate_status(9), usb4_port_retimer_nvm_read(9), usb4_usb3_port_max_link_rate(9), usb4_usb3_port_allocated_bandwidth(9), usb4_usb3_port_allocate_bandwidth(9), usb4_usb3_port_release_bandwidth(9), usb4_dp_port_set_cm_id(9), usb4_dp_port_bandwidth_mode_supported(9), usb4_dp_port_bandwidth_mode_enabled(9), usb4_dp_port_set_cm_bandwidth_mode_supported(9), usb4_dp_port_group_id(9), usb4_dp_port_set_group_id(9), usb4_dp_port_nrd(9), usb4_dp_port_set_nrd(9), usb4_dp_port_granularity(9), usb4_dp_port_set_granularity(9), usb4_dp_port_set_estimated_bandwidth(9), usb4_dp_port_allocated_bandwidth(9), usb4_dp_port_allocate_bandwidth(9), usb4_dp_port_requested_bandwidth(9), usb4_pci_port_set_ext_encapsulation(9), usb4_pci_port_ltssm_state(9)

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and that's the page!! this one came from ./drivers/thunderbolt, dated October 2026, and it's filed under the name usb4_switch_map_pcie_down(9) — go read it again, i'll wait 💖✨🎀