STRUCT TB_PORT(9)

🌸 NAME 🌸

okay so bestie, welcome to struct tb_port(9) from the Kernel API Manual — this is literally a thunderbolt port, and it’s part of a tb_switch. iconic little kernel struct behavior, no cap. 💅

✨ SYNOPSIS ✨

struct tb_port {
    struct tb_regs_port_header config;
    struct tb_switch *sw;
    struct tb_port *remote;
    struct tb_xdomain *xdomain;
    int cap_phy;
    int cap_tmu;
    int cap_adap;
    int cap_usb4;
    struct usb4_port *usb4;
    u8 port;
    bool disabled;
    bool bonded;
    struct tb_port *dual_link_port;
    u8 link_nr:1;
    struct ida in_hopids;
    struct ida out_hopids;
    struct list_head list;
    unsigned int total_credits;
    unsigned int ctl_credits;
    unsigned int dma_credits;
    struct tb_bandwidth_group *group;
    struct list_head group_list;
    unsigned int max_bw;
    bool redrive;
};

👑 Members 👑

• config — cached port configuration read from registers. 💖
• sw — the switch this port belongs to.
• remote — the remote port, or NULL if it’s not connected.
• xdomain — the remote host, or NULL if it’s not connected.
• cap_phy — offset, zero if not found.
• cap_tmu — offset of the adapter-specific TMU capability, or 0 if not present.
• cap_adap — offset of the adapter-specific capability, or 0 if not present.
• cap_usb4 — offset to the USB4 port capability, or 0 if not present.
• usb4 — pointer to the USB4 port structure, only if cap_usb4 is != 0.
• port — port number on the switch.
• disabled — disabled by eeprom, or enabled but not implemented.
• bonded — true if the port is bonded (two lanes combined as one).
• dual_link_port — if the switch is connected using two ports, this points to the other port.
• link_nr — is this the primary or secondary port on the dual_link.
• in_hopids — currently allocated input HopIDs.
• out_hopids — currently allocated output HopIDs.
• list — used to link ports to the DP resources list.
• total_credits — total number of buffers available for this port.
• ctl_credits — buffers reserved for the control path.
• dma_credits — number of credits allocated for DMA tunneling for all DMA paths through this port.
• group — bandwidth allocation group the adapter is assigned to. only used for DP IN adapters for now.
• group_list — the adapter is linked to the group’s list of ports through this.
• max_bw — maximum possible bandwidth through this adapter if set to non-zero.
• redrive — for DP IN, if true the adapter is in redrive mode.

🧚 Description 🧚

In USB4 terminology, this structure represents an adapter — protocol or lane adapter. periodt. 🦋

💜 SEE ALSO 💜

• Kernel file ./drivers/thunderbolt/tb.h
• struct tb_nvm(9)
• enum tb_switch_tmu_mode(9)
• struct tb_switch_tmu(9)
• struct tb_switch(9)
• struct tb_bandwidth_group(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)

mwah 💅 — source ./drivers/thunderbolt, October 2026.