usb4_switch_setup(9)

📦 version 7.3.1, in nixpkgs unstable

💅 usb4_switch_setup — the kernel API manual, bestie edition ✨

okay so real talk, this is a page out of the Kernel API Manual (usb4_switch_setup(9)), and honestly? it's a little guy with a big job. let's get into it 🫶

🌸 NAME 🌸

usb4_switch_setup — the extra setup pass for a USB4 device, because apparently routers can't just show up and be ready, they need a whole glow-up first 💅

✨ SYNOPSIS ✨

int usb4_switch_setup (struct tb_switch *sw );

🎀 ARGUMENTS 🎀

  • sw — the USB4 router we're setting up. that's the main character of this function, no cap 👑

🦋 DESCRIPTION 🦋

so here's the tea: USB4 routers need additional settings before all the tunneling can actually happen. like, they're not gonna just tunnel on vibes alone. this function turns on USB tunneling and PCIe tunneling — but only if it can be enabled, iykyk. the "if it can" part matters: for example, the parent switch also has to support them.

and if USB tunneling just isn't available for some reason — say there's a Thunderbolt 3 switch upstream being a whole obstacle 😭 — then the internal xHCI controller gets enabled instead. we pivot, we adapt, we slay differently 💁‍♀️

⚠️ important bestie: this does not set the configuration valid bit of the router. to do that, you gotta call usb4_switch_configuration_valid. don't skip that step, fr fr 🙈

🌈 RETURN 🌈

  • 0 on success 🎉
  • a negative errno otherwise 💀

💜 SEE ALSO 💜

the kernel file lives at ./drivers/thunderbolt/usb4.c, and here's the whole extended friend group — every single one, don't @ me, they all matter:

okay that's the whole page!! 💖 this one comes from the source directory ./drivers/thunderbolt, dated October 2026, and it's filed under usb4_switch_setup(9) — go read the neighbors too, they're all icons in their own right 🧚‍♀️⭐

📦 where this page comes from