usb4_switch_credits_init(9)

💅 usb4_switch_credits_init(9) — from the Kernel API Manual, bestie 🎀

okay so real talk, this is a kernel API page and the manual it lives in is literally called Kernel API Manual, so you already know we're in the grown-up zone. grab a strawberry drink 🍓 and let's get into it.

---

✨ NAME ✨

usb4_switch_credits_init — bestie, this one reads buffer allocation parameters. that's the whole job. she reads the params, that's her moment 💅

---

✨ SYNOPSIS ✨

int usb4_switch_credits_init (struct tb_switch *sw );

---

✨ ARGUMENTS ✨

• sw — the USB4 router. yes, THE router. main character energy only 👑

---

✨ DESCRIPTION ✨

so what she does is: she reads the sw buffer allocation parameters, and then she initializes the sw buffer allocation fields accordingly. like, she's matching the fit to the router, no cap 🦋

and specifically — write this down because this is the actual point of the whole function — sw->credits_allocation gets set to true if these parameters can be used in tunneling. that's the vibe check the entire function is doing, fr fr ✨

---

✨ RETURN ✨

• 0 on success 🎉
• a negative errno otherwise 😭 (yes, negative. it's giving "something went wrong in a very Linux way")

---

✨ SEE ALSO ✨

the kernel file she lives in is ./drivers/thunderbolt/usb4.c, and omg the friend group on this page is HUGE. literally the whole thunderbolt roster showed up 🌈 here's everybody, in order:

• 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_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)

like… she knows everybody. iykyk 🫶

---

ngl the whole page is short and sweet, but that credits_allocation flag is the moment. don't skip it. 💜

and that's the tea! 🎀 this lil legend lives in ./drivers/thunderbolt, and the page is dated October 2026 — so yeah, she's from the future and still slaying. bye bestie, go read some buffer allocation parameters 💅✨🌸