cxl_port_attach_region(9)

💅 cxl_port_attach_region(9) — a Kernel API Manual moment

okay bestie, welcome to the cxl_port_attach_region page ✨ this one lives in the Kernel API Manual, and honestly it's giving "the friend who keeps the group chat's plans straight" energy 🫶

---

🎀 NAME 🎀

cxl_port_attach_region — track a region's interest in a port by endpoint 💖

like, it's the lil bookkeeper that remembers "hey, this region cares about this port, and here's which endpoint is why" 🦋

---

✨ SYNOPSIS ✨

int cxl_port_attach_region (struct cxl_port *port , struct cxl_region
*cxlr , struct cxl_endpoint_decoder *cxled , int pos );

that's the whole vibe: you hand it a port, a region, an endpoint decoder, and a position, and it returns an int — periodt 💅

---

🌸 ARGUMENTS 🌸

• port — the port we're adding a brand-new region reference to, as in a struct cxl_region_ref 🎀
• cxlr — the region being attached to the port 💖
• cxled — the endpoint decoder that's doing the work of creating the region reference, or pinning down a reference that already exists 📌
• pos — the interleave position of cxled inside cxlr ⭐

---

🔥 DESCRIPTION 🔥

okay so the attach event? it's literally an opportunity 👑 it's the moment where the kernel gets to validate the CXL decode setup constraints, and also record the metadata it's gonna need later for programming the HDM decoders — and in particular, decoder target lists 🎯

the steps, in order, no cap:

1. validate that there are no other regions with a higher HPA already associated with port 🚨
2. establish a region reference if one is not already present 🧚
3. additionally allocate a decoder instance that will host cxlr on port 💫
4. pin the region reference by the endpoint 📍
5. account for how many entries in port's target list are needed to cover all of the added endpoints 🧮

ngl step one is the vibe check 👀 — no other region with a higher HPA is allowed to already be hanging out with port.

---

🦋 SEE ALSO 🦋

• Kernel file ./drivers/cxl/core/region.c cxl core region(9) 🔍
• cxl_port_pick_region_decoder(9)
• cxl_calc_interleave_pos(9)
• devm_cxl_add_region(9)
• cxl_validate_translation_params(9)

go read the whole friend group, they're all iconic 💜

---

and that's the page, bestie 🌈 sign-off time: this lil gem comes to you from ./drivers/cxl/core, dated October 2026 — screenshot it, cite it, slay 💅🎀✨