xhci_get_endpoint_index(9)

✨ xhci_get_endpoint_index(9) ✨

okay bestie, welcome to the Kernel API Manual 💅 this one's a lil function from the USB host controller world and honestly it's giving "tiny but crucial" energy 🎀

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🌸 NAME 🌸

xhci_get_endpoint_index — the lil helper used for passing endpoint bitmasks between the core and HCDs 🫶 its whole job? find the index for an endpoint given its descriptor. then you take the return value and right shift 1 by it to get your bitmask. iconic behavior, no cap ✨

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🦋 SYNOPSIS 🦋

unsigned int xhci_get_endpoint_index (struct usb_endpoint_descriptor
*desc );

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💖 ARGUMENTS 💖

• desc — the USB endpoint descriptor you wanna determine the index for 💫

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👑 DESCRIPTION 👑

so here's the math bestie, and it's literally this:

Index = (epnum * 2) + direction - 1

where direction = 0 for OUT and 1 for IN 🌈

and for control endpoints? the IN index is the one that gets used (the OUT index is unused, lowkey just sitting there 🙈), so it works out to:

index = (epnum * 2) + direction - 1 = (epnum * 2) + 1 - 1 = (epnum * 2)

math ate that fr fr 🔥

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🧚 SEE ALSO 🧚

• Kernel file ./drivers/usb/host/xhci.c
• xhci_setup_device(9)

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that's the whole page, bestie — short, sweet, and mathematically slay 💜

sign-off szn 🎀 this one lives in ./drivers/usb/host, dated October 2026, and it's page xhci_get_endpoint_index(9) of the Kernel API Manual — go forth and right shift that 1 responsibly ✨💖