STRUCT CXL_MBOX_CMD(9)

💖 NAME 💖

struct cxl_mbox_cmd — bestie, this is literally the command that gets submitted to hardware ✨ like it's the little envelope you hand over to the hardware and you're like "here, do this for me, ily" 🫶

🌸 SYNOPSIS 🌸

struct cxl_mbox_cmd {
    u16 opcode;
    void *payload_in;
    void *payload_out;
    size_t size_in;
    size_t size_out;
    size_t min_out;
    int poll_count;
    int poll_interval_ms;
    u16 return_code;
 };

🎀 MEMBERS 🎀

• opcode — (input) the command set, plus the actual command you're submitting to hardware. it's giving "who are you and what do you want" 💅
• payload_in — (input) a pointer to the input payload. the little gift bag of data you're sending in 🎁
• payload_out — (output) pointer to the output payload. ngl, the caller has to allocate it — that's on you bestie, no cap 🙈
• size_in — (input) how many bytes to load from payload_in. count 'em fr fr 🔢
• size_out — (input) the max number of bytes loaded into payload_out. (output) the number of bytes actually generated by the device. for fixed-size output commands this is always expected to be deterministic (iconic, predictable behaviour ✨). for variable-sized output commands, it tells you the exact number of bytes written. so it's doing double duty and honestly? main character energy 👑
• min_out — (input) the internal command output payload size validation. like a bouncer checking the payload is big enough 🚪
• poll_count — (input) the number of timeouts to attempt. how many chances you're giving it before you're like "ok I'm done" 💀
• poll_interval_ms — (input) the time between mailbox background command polling interval timeouts. the lil breather between checks ⏳
• return_code — (output) the error code returned from hardware. the hardware's final verdict on your request 🫡

🦋 DESCRIPTION 🦋

okay so this is the primary mechanism used to send commands to the hardware. like, this is the way. periodt 💅

all the fields except payload_* correspond exactly to the fields described in the Command Register section of CXL 2.0 8.2.8.4.5. not approximately. exactly. we don't do approximation here 🎯

and then payload_in and payload_out get written to, and read from, the Command Payload Registers defined in CXL 2.0 8.2.8.4.8. iykyk 🌈

⭐ SEE ALSO ⭐

• Kernel file ./include/cxl/mailbox.h
• struct cxl_mailbox(9)

okay that's the whole page bestie, go forth and submit commands responsibly 🧚‍♀️✨ this lil writeup lives in ./include/cxl and it's dated October 2026 — mwah, bye! 💜🎀