usb4_switch_nvm_write(9)

📦 version 7.3.1, in nixpkgs unstable

💾 usb4_switch_nvm_write(9) — kernel API manual, bestie edition ✨

Okay so bestie, listen — this is a page from the Kernel API Manual about usb4_switch_nvm_write, and it's lowkey iconic. We're writing bytes straight into a router's NVM. No cap. Let's get into it 💅

🌸 NAME 🌸

usb4_switch_nvm_write — write to the router NVM 🎀

✨ SYNOPSIS ✨

int usb4_switch_nvm_write (struct tb_switch *sw , unsigned int address ,
const void *buf , size_t size );

That's the whole vibe right there. Four arguments, one int coming back at you 🫶

🦋 ARGUMENTS 🦋

  • sw — the USB4 router you're doing this to. main character energy, honestly 👑
  • address — the start address where the write happens, measured in bytes. Where we begin, bestie 📍
  • buf — a pointer to the data you're writing. this is the payload, the moment, the whole point 💖
  • size — how big buf is, in bytes. gotta know how much we're working with 📏

💜 DESCRIPTION 💜

So what does it do? It writes buf to the router NVM, using USB4 router operations. That's it. That's the slay. Straight-up persistent-ish storage writing through router ops, no drama 🔥

Like… it's literally giving "I know exactly what I'm doing." NVM write through the proper USB4 router path, periodt 💅

⭐ RETURN ⭐

  • 0 — write completed successfully. we love a win 🎉
  • -EOPNOTSUPP — NVM write not supported. so like, this router said "not today" 😭
  • Negative errno — another error occurred. some other little gremlin showed up, check your errno 🙈

🌈 SEE ALSO 🌈

Everything lives in the kernel file ./drivers/thunderbolt/usb4.c, and honestly the whole friend group is here — go say hi to all of them 🫶:

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_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_pcie_down(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)

Heads up bestie: -EOPNOTSUPP means the router genuinely can't do NVM writes — it's not you, it's the hardware 💀

And that's the page!! This one's filed under ./drivers/thunderbolt, dated October 2026, from the Kernel API Manual — ty for reading, ily, go write some NVM bytes responsibly 🧚💖✨

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