config_ep_by_speed_and_alt(9)

💅 config_ep_by_speed_and_alt(9) — kernel API manual realness ✨

okay so this is a kernel API manual page, bestie, and the function in question is config_ep_by_speed_and_alt — it literally configures the given endpoint according to gadget speed. no cap, that's the whole ~vibe~ of the NAME section. 🎀

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🌸 SYNOPSIS 🌸

int config_ep_by_speed_and_alt (struct usb_gadget *g , struct usb_function *f , struct usb_ep *_ep , u8 alt );

that's the whole signature, copy it exactly pls, we don't freestyle here 💅

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🦋 ARGUMENTS 🦋

• g — pointer to the gadget, your main character struct fr
• f — usb function, she's the function in question
• _ep — the endpoint to configure, the one getting the glow-up
• alt — alternate setting number, a u8, keep her typed correctly

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⭐ RETURN ⭐

returns an error code — and 0 on success, which is the only number we're emotionally invested in honestly 🫶

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💖 DESCRIPTION 💖

so what does she actually do? This function chooses the right descriptors for a given endpoint according to gadget speed, and saves it in the endpoint desc field. iconic behavior, no notes.

and if the endpoint already has a descriptor assigned to it — that's right, she overwrites it with the currently corresponding descriptor. not me casually replacing your descriptor 🙈 it's fine, it's intentional, it's in the spec.

also bestie, the endpoint maxpacket field gets updated according to the chosen descriptor. so the maxpacket stays in sync with whatever descriptor got picked — slay. ✨

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🎀 NOTE 🎀

the supplied function should hold all the descriptors for supported speeds — like, all of them, every speed, no leaving some at home. this is a hard requirement, not a suggestion, iykyk 💀

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🌈 SEE ALSO 🌈

Kernel file ./drivers/usb/gadget/composite.c — that's where the lore lives, go read her 👑

• struct usb_os_string(9)
• function_descriptors(9)
• next_desc(9)
• config_ep_by_speed(9)
• usb_add_function(9)
• usb_function_deactivate(9)
• usb_function_activate(9)
• usb_interface_id(9)
• usb_func_wakeup(9)
• bos_desc(9)
• usb_add_config(9)
• usb_string_id(9)
• usb_string_ids_tab(9)
• usb_gstrings_attach(9)
• usb_string_ids_n(9)
• usb_composite_probe(9)
• usb_composite_unregister(9)
• usb_composite_setup_continue(9)

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okay that's the page!! 💜 this gem comes to you from ./drivers/usb/gadget, dated October 2026, and the page is — say it with me — config_ep_by_speed_and_alt(9). periodt. 🦋✨