STRUCT TB_SWITCH(9)

✨ NAME ✨

struct tb_switch — a thunderbolt switch, bestie 💅 (and yeah, this is that tb_switch(9) page you were looking for)

Okay so real quick — this is a page from the Kernel API Manual, and it's lowkey all about one struct. Buckle up, she's a big one 🎀

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🌸 SYNOPSIS 🌸

struct tb_switch {
    struct device dev;
    struct tb_regs_switch_header config;
    struct tb_port *ports;
    struct tb_dma_port *dma_port;
    struct tb_switch_tmu tmu;
    struct tb *tb;
    u64 uid;
    uuid_t *uuid;
    u16 vendor;
    u16 device;
    const char *vendor_name;
    const char *device_name;
    unsigned int link_speed;
    enum tb_link_width link_width;
    enum tb_link_width preferred_link_width;
    bool link_usb4;
    unsigned int generation;
    int cap_plug_events;
    int cap_vsec_tmu;
    int cap_lc;
    int cap_lp;
    bool is_unplugged;
    u8 *drom;
    struct tb_nvm *nvm;
    bool no_nvm_upgrade;
    bool safe_mode;
    bool boot;
    bool rpm;
    unsigned int authorized;
    enum tb_security_level security_level;
    struct dentry *debugfs_dir;
    u8 *key;
    u8 connection_id;
    u8 connection_key;
    u8 link;
    u8 depth;
    struct completion rpm_complete;
    unsigned long quirks;
    bool credit_allocation;
    unsigned int max_usb3_credits;
    unsigned int min_dp_aux_credits;
    unsigned int min_dp_main_credits;
    unsigned int max_pcie_credits;
    unsigned int max_dma_credits;
    unsigned int clx;
  #ifdef CONFIG_DEBUG_FS;
    struct debugfs_blob_wrapper drom_blob;
  #endif;
};

No cap, that's the whole thing verbatim 💀 copy it exactly, don't be cute with it.

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🦋 MEMBERS 🦋

Okay so every single field, one by one, no skipping, we're getting through this together 🫶

• dev — The device for the switch. Her actual device struct, the whole reason she shows up in sysfs and all that.
• config — The switch configuration. It's a struct tb_regs_switch_header, iykyk.
• ports — The ports in this switch. Plural, she has many ✨
• dma_port — So if the switch has a port that supports the DMA-configuration-based mailbox, this bad boy holds a pointer to it (NULL otherwise). And it's giving multipurpose, because if it's set, that also means the switch has upgradeable NVM 👑
• tmu — The switch TMU configuration.
• tb — Pointer to the domain the switch belongs to.
• uid — The unique ID of the switch. Very main character, very one-of-one 💅
• uuid — The UUID of the switch, or NULL if that's not supported.
• vendor — Vendor ID of the switch.
• device — Device ID of the switch.
• vendor_name — Name of the vendor, or NULL if it's not known. Not us guessing, that's literally what the field says 🙈
• device_name — Name of the device, or NULL if it's not known.
• link_speed — Speed of the link, in Gb/s.
• link_width — Width of the upstream facing link.
• preferred_link_width — The router's preferred link width, and heads up: this is only set for Gen 4 links 👀
• link_usb4 — Whether the upstream link is USB4.
• generation — The switch's Thunderbolt generation.
• cap_plug_events — Offset to the plug events capability (0 if it's not found).
• cap_vsec_tmu — Offset to the TMU vendor specific capability (0 if it's not found).
• cap_lc — Offset to the link controller capability (0 if it's not found).
• cap_lp — Offset to the low power (CLx for TBT) capability (0 if it's not found).
• is_unplugged — The switch is going away 😭 yeah, she's leaving.
• drom — The DROM of the switch (NULL if it's not found).
• nvm — Pointer to the NVM if the switch has one (NULL otherwise).
• no_nvm_upgrade — Prevents NVM upgrade of this switch. Respect the boundary 🚫
• safe_mode — The switch is in safe-mode.
• boot — Whether the switch was already authorized on boot or not.
• rpm — The switch supports runtime PM.
• authorized — Whether the switch is authorized by user or policy.
• security_level — The switch's supported security level. It's an enum tb_security_level, look it up bestie 🔐
• debugfs_dir — Pointer to the debugfs structure.
• key — Contains the key used to challenge the device, or NULL if it's not supported. Size of the key is TB_SWITCH_KEY_SIZE — write that down ✍️
• connection_id — Connection ID used with ICM messaging.
• connection_key — Connection key used with ICM messaging.
• link — Root switch link this switch is connected to (ICM only).
• depth — Depth in the chain this switch is connected at (ICM only).
• rpm_complete — Completion used to wait for runtime resume to complete (ICM only).
• quirks — Quirks used for this Thunderbolt switch. Everybody's got their little quirks fr fr 💀
• credit_allocation — Are the below buffer allocation parameters valid. She's the vibe check for the next five fields 🌈
• max_usb3_credits — Router preferred number of buffers for USB 3.x.
• min_dp_aux_credits — Router preferred minimum number of buffers for DP AUX. Note the minimum, don't get it twisted 🎀
• min_dp_main_credits — Router preferred minimum number of buffers for DP MAIN.
• max_pcie_credits — Router preferred number of buffers for PCIe.
• max_dma_credits — Router preferred number of buffers for DMA/P2P.
• clx — CLx states on the upstream link of the router.
• drom_blob — DROM debugfs blob wrapper. And psst — this one lives inside #ifdef CONFIG_DEBUG_FS;, so she only exists when debugfs is configured 🧚

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💜 DESCRIPTION 💜

So here's the important bit, don't skip it:

When the switch is being added or removed to the domain (other switches), you need to have the domain lock held. 🔒 Like, non-negotiable. Hold the lock. That's the rule.

And in USB4 terminology, this structure represents a router. Same girl, different name, periodt 💅

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⭐ SEE ALSO ⭐

Kernel file ./drivers/thunderbolt/tb.h — and like, all of these, in one big group-chat of related pages:

struct tb_nvm(9), enum tb_switch_tmu_mode(9), struct tb_switch_tmu(9), struct tb_bandwidth_group(9), struct tb_port(9), struct usb4_port(9), struct tb_retimer(9), struct tb_path_hop(9), enum tb_path_port(9), struct tb_path(9), struct tb_cm_ops(9), tb_upstream_port(9), tb_is_upstream_port(9), tb_port_has_remote(9), tb_domain_event(9), tb_switch_for_each_port(9), tb_switch_downstream_port(9), tb_switch_depth(9), tb_switch_is_icm(9), tb_switch_tmu_is_configured(9), tb_switch_tmu_is_enabled(9), tb_switch_clx_is_enabled(9), tb_port_path_direction_downstream(9), tb_for_each_port_on_path(9), tb_for_each_upstream_port_on_path(9), tb_path_for_each_hop(9), tb_downstream_route(9), tb_xdomain_downstream_port(9), usb4_switch_version(9), tb_switch_is_usb4(9), enum usb4_sb_target(9), enum usb4_margin_sw_error_counter(9), struct usb4_port_margining_params(9)

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That's the whole page, bestie — go read some kernel source, you ate this 💖✨

Signed off from ./drivers/thunderbolt, dated October 2026, page struct tb_switch(9) — mwah 🎀🫶