STRUCT USB_GADGET(9)

💖 struct usb_gadget(9) — Kernel API Manual 💖

💖 NAME 💖

struct usb_gadget — represents a usb device. That's literally the whole name, bestie. 🫶

✨ SYNOPSIS ✨

okay so here's the full struct, no cap — every field exactly as listed, so don't go renaming anything 💅:

struct usb_gadget {
    struct work_struct              work;
    struct usb_udc                  *udc;
    const struct usb_gadget_ops     *ops;
    struct usb_ep                   *ep0;
    struct list_head                ep_list;
    enum usb_device_speed           speed;
    enum usb_device_speed           max_speed;
    enum usb_ssp_rate               ssp_rate;
    enum usb_ssp_rate               max_ssp_rate;
    enum usb_device_state           state;
    spinlock_t state_lock;
    bool teardown;
    const char                      *name;
    struct device                   dev;
    unsigned isoch_delay;
    unsigned out_epnum;
    unsigned in_epnum;
    unsigned mA;
    struct usb_otg_caps             *otg_caps;
    unsigned sg_supported:1;
    unsigned is_otg:1;
    unsigned is_a_peripheral:1;
    unsigned b_hnp_enable:1;
    unsigned a_hnp_support:1;
    unsigned a_alt_hnp_support:1;
    unsigned hnp_polling_support:1;
    unsigned host_request_flag:1;
    unsigned quirk_ep_out_aligned_size:1;
    unsigned quirk_altset_not_supp:1;
    unsigned quirk_stall_not_supp:1;
    unsigned quirk_zlp_not_supp:1;
    unsigned quirk_avoids_skb_reserve:1;
    unsigned is_selfpowered:1;
    unsigned deactivated:1;
    unsigned connected:1;
    unsigned lpm_capable:1;
    unsigned wakeup_capable:1;
    unsigned wakeup_armed:1;
    int irq;
    int id_number;
 };

🎀 Members 🎀

these are the members one by one, with zero skipped because we do not do that here 💅

• work — (internal use) Workqueue to be used for sysfs_notify. 🛠️
• udc — struct usb_udc pointer for this gadget. 👑
• ops — Function pointers used to access hardware-specific operations. 🔌
• ep0 — Endpoint zero, used when reading or writing responses to driver setup requests. 🎯
• ep_list — List of other endpoints supported by the device. 📋
• speed — Speed of current connection to USB host. 🚀
• max_speed — Maximal speed the UDC can handle. UDC must support this and all slower speeds. 🏁
• ssp_rate — Current connected SuperSpeed Plus signaling rate and lane count. ⚡
• max_ssp_rate — Maximum SuperSpeed Plus signaling rate and lane count the UDC can handle. The UDC must support this and all slower speeds and lower number of lanes. 🔥
• state — the state we are now (attached, suspended, configured, etc). 📍
• state_lock — Spinlock protecting the state and teardown members. 🔒
• teardown — True if the device is undergoing teardown, used to prevent new work from being scheduled during cleanup. 🧹
• name — Identifies the controller hardware type. Used in diagnostics and sometimes configuration. 🏷️
• dev — Driver model state for this abstract device. 🧬
• isoch_delay — value from Set Isoch Delay request. Only valid on SS/SSP. ⏱️
• out_epnum — last used out ep number. ⬅️
• in_epnum — last used in ep number. ➡️
• mA — last set mA value. 🔋
• otg_caps — OTG capabilities of this gadget. 🦋
• sg_supported — true if we can handle scatter-gather. 🧩
• is_otg — True if the USB device port uses a Mini-AB jack, so that the gadget driver must provide a USB OTG descriptor. 🔄
• is_a_peripheral — False unless is_otg, the "A" end of a USB cable is in the Mini-AB jack, and HNP has been used to switch roles so that the "A" device currently acts as A-Peripheral, not A-Host. 🙃
• b_hnp_enable — OTG device feature flag, indicating that the A-Host enabled HNP support. 🫶
• a_hnp_support — OTG device feature flag, indicating that the A-Host supports HNP at this port. 🛟
• a_alt_hnp_support — OTG device feature flag, indicating that the A-Host only supports HNP on a different root port. 🌱
• hnp_polling_support — OTG device feature flag, indicating if the OTG device in peripheral mode can support HNP polling. 📡
• host_request_flag — OTG device feature flag, indicating if A-Peripheral or B-Peripheral wants to take host role. 👑
• quirk_ep_out_aligned_size — epout requires buffer size to be aligned to MaxPacketSize. 📏
• quirk_altset_not_supp — UDC controller doesn't support alt settings. 🚫
• quirk_stall_not_supp — UDC controller doesn't support stalling. 💀
• quirk_zlp_not_supp — UDC controller doesn't support ZLP. 🙈
• quirk_avoids_skb_reserve — udc/platform wants to avoid skb_reserve in u_ether.c to improve performance. 🏎️
• is_selfpowered — if the gadget is self-powered. 🔌
• deactivated — True if gadget is deactivated - in deactivated state it cannot be connected. ⛔
• connected — True if gadget is connected. ✅
• lpm_capable — If the gadget max_speed is FULL or HIGH, this flag indicates that it supports LPM as per the LPM ECN & errata. 🌀
• wakeup_capable — True if gadget is capable of sending remote wakeup. 📣
• wakeup_armed — True if gadget is armed by the host for remote wakeup. 🎯
• irq — the interrupt number for device controller. ⚡
• id_number — a unique ID number for ensuring that gadget names are distinct. 🆔

💅 Description 💅

okay so picture this: Gadgets have a mostly-portable "gadget driver" implementing device functions, handling all usb configurations and interfaces. Gadget drivers talk to hardware-specific code indirectly, through ops vectors. That insulates the gadget driver from hardware details, and packages the hardware endpoints through generic i/o queues. The "usb_gadget" and "usb_ep" interfaces provide that insulation from the hardware. 🧚

Except for the driver data, all fields in this structure are read-only to the gadget driver. That driver data is part of the "driver model" infrastructure in 2.6 (and later) kernels, and for earlier systems is grouped in a similar structure that's not known to the rest of the kernel. 🔒

Values of the three OTG device feature flags are updated before the setup call corresponding to USB_REQ_SET_CONFIGURATION, and before driver suspend calls. They are valid only when is_otg, and when the device is acting as a B-Peripheral (so is_a_peripheral is false). 🫶

🌈 SEE ALSO 🌈

Kernel file ./include/linux/usb/gadget.h has the whole friend group — bestie, go read these too, iykyk:

• struct usb_request(9)
• struct usb_ep_caps(9)
• struct usb_ep(9)
• free_usb_request(9)
• usb_ep_align(9)
• usb_ep_align_maybe(9)
• gadget_is_altset_supported(9)
• gadget_is_stall_supported(9)
• gadget_is_zlp_supported(9)
• gadget_avoids_skb_reserve(9)
• gadget_is_dualspeed(9)
• gadget_is_superspeed(9)
• gadget_is_superspeed_plus(9)
• gadget_is_otg(9)
• struct usb_gadget_driver(9)
• usb_gadget_register_driver_owner(9)
• usb_gadget_unregister_driver(9)
• struct usb_string(9)
• struct usb_gadget_strings(9)
• usb_free_descriptors(9)

okay that's the whole page, bestie — source/version is ./include/linux/usb, dated October 2026, and the page itself is struct usb_gadget(9). mwah 💋✨