hl_fw_send_cpu_message(9)

💌 hl_fw_send_cpu_message(9) — or, how to slide into your device CPU's DMs

okay so bestie, welcome to the Kernel API Manual ✨ this one's a kernel function, hl_fw_send_cpu_message, and its whole personality is: send a CPU message to the device. that's it. that's the vibe. let's get into it 🫶

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✨ SYNOPSIS ✨

int hl_fw_send_cpu_message (struct hl_device *hdev , u32 hw_queue_id ,
u32 *msg , u16 size , u32 timeout_us , u64 *result );

like, look at her. six params, one int return, zero notes. iconic behavior fr fr 💅

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🎀 ARGUMENTS 🎀

• hdev — pointer to hl_device structure. literally the device, the whole main character 👑
• hw_queue_id — the HW queue ID 🦋 (yes she has a queue number, respect it)
• msg — raw data of the message/packet. no makeup, no filter, just raw bytes 💀
• size — size of msg in bytes. it's a u16, keep it cute 🎀
• timeout_us — timeout in usec to wait for CPU reply on the message. the "how long do I sit by my phone waiting for a text back" window ⏳
• result — return code reported by FW. the receipts, basically 🧾

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🌸 DESCRIPTION 🌸

send message to the device CPU. that's literally the entire description, she's a woman of few words and honestly? obsessed 🎯 no cap, that's the whole functionality — you're passing a message to the device CPU, that's the assignment.

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🔥 RETURN 🔥

• 0 on success — slay 💖
• non-zero for failure — and here's the specific breakdown, iykyk:
  • -ENOMEM — memory allocation failure 😭 the malloc said no
  • -EAGAIN — CPU is disabled (try again when enabled) 🙈 she's not taking calls rn, try later
  • -ETIMEDOUT — timeout waiting for FW response ⏰ left on read, tragic
  • -EIO — protocol error 💀 something got miscommunicated in the group chat

ngl, that -EAGAIN one is important — it's not a dead end, it's a "not right now." try again when the CPU is enabled, bestie 🫶

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🦋 SEE ALSO 🦋

Kernel file ./drivers/accel/habanalabs/common/firmware_if.c — that's where she lives 🏠

and the whole friend group, in order:

hl_fw_version_cmp(9), extract_u32_until_given_char(9), hl_get_sw_major_minor_subminor(9), hl_get_preboot_major_minor(9), hl_release_firmware(9), hl_fw_copy_fw_to_device(9), hl_fw_copy_msg_to_device(9), hl_fw_load_fw_to_device(9), hl_fw_preboot_update_state(9), hl_fw_dynamic_report_error_status(9), hl_fw_dynamic_send_cmd(9), hl_fw_dynamic_extract_fw_response(9), hl_fw_dynamic_wait_for_status(9), hl_fw_dynamic_send_clear_cmd(9), hl_fw_dynamic_send_protocol_cmd(9), hl_fw_compat_crc32(9), hl_fw_dynamic_validate_memory_bound(9), hl_fw_dynamic_validate_descriptor(9), hl_fw_dynamic_read_and_validate_descriptor(9), hl_fw_dynamic_request_descriptor(9), hl_fw_dynamic_read_device_fw_version(9), hl_fw_dynamic_copy_image(9), hl_fw_dynamic_copy_msg(9), hl_fw_boot_fit_update_state(9), hl_fw_dynamic_load_image(9), hl_fw_linux_update_state(9), hl_fw_dynamic_send_msg(9), hl_fw_dynamic_init_cpu(9), hl_fw_static_init_cpu(9), hl_fw_init_cpu(9)

like. that's the whole squad. go read them too, they're all eating 🔥

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and that's the page, bestie!! source path is ./drivers/accel/habanalabs/common, and this lil icon was dated October 2026 — so go forth, send your CPU message, and remember: 0 means success, and success means slay 🌈✨💜