__cxl_pci_mbox_send_cmd(9)

💌 __cxl_pci_mbox_send_cmd(9) — Kernel API Manual, but make it make sense

okay so bestie, grab your iced matcha 🍓 because we're diving into the Kernel API Manual and today's main character is __cxl_pci_mbox_send_cmd — aka the function that literally just executes a mailbox command. That's it, that's the vibe. ✨

---

✨ NAME ✨

__cxl_pci_mbox_send_cmd — execute a mailbox command 💅

---

🎀 SYNOPSIS 🎀

int __cxl_pci_mbox_send_cmd (struct cxl_mailbox *cxl_mbox , struct
       cxl_mbox_cmd *mbox_cmd );

like, it takes two pointers and gives you back an int. no cap. 🫶

---

🦋 ARGUMENTS 🦋

• cxl_mbox — the CXL mailbox context, aka the whole entire setting, the stage, the environment 🌸
• mbox_cmd — the command you're sending to the memory device. this is the actual message, the ~content~ 👑

---

👑 CONTEXT 👑

Any context. literally any. Any context. but — and this is the important part, bestie — it expects mbox_mutex to be held. so like, hold the lock or perish 🔥 (not literally perish but you know what I mean).

---

💖 RETURN 💖

• -ETIMEDOUT — if a timeout occurred waiting for completion 😭 like it was waiting and waiting and the clock ran out
• 0 — on success 🎉 slay

⚠️ okay so this is the part people always skip and I cannot let you skip it: the caller should check the return code in mbox_cmd to make sure it succeeded. yes, even if this function returns 0. yes, both. check the one inside mbox_cmd. iykyk 🙈

---

🌈 DESCRIPTION 🌈

so this is the generic form of the CXL mailbox send command — meaning it only uses the registers defined by the mailbox capability ID, specifically CXL 2.0 8.2.8.4. iconic spec energy 📖✨

Memory devices, and perhaps other types of CXL devices, may have further information available upon error conditions 👀 like they might have ✨extra tea✨ to spill when something goes wrong.

Driver facilities that wish to send mailbox commands should use the wrapper command. not this raw one. use the wrapper. be a wrapper girlie 💅

aaaand now the lore 🧚: the CXL spec allows for up to two mailboxes. the intention is:

• the primary mailbox → OS controlled 🖥️
• the secondary mailbox → used by system firmware 🔧

this is so the OS and the firmware can communicate with the device and not need to coordinate with each other — like two besties texting the same group chat without ever planning it 🫶

and the driver? the driver only uses the primary mailbox. periodt. 🎀

---

⭐ SEE ALSO ⭐

• Kernel file ./drivers/cxl/pci.c
• cxl
• pci(9)

---

okay that's the whole page, you ate that 💜 go forth and hold your mutex bestie. this was the Kernel API Manual, ./drivers/cxl, October 2026 — mwah, see you in the next manpage 💋🎀🦋