acpi_processor_evaluate_cst(9)

💅 acpi_processor_evaluate_cst(9) — the Kernel API Manual, bestie edition

okay so this one lives in the Kernel API Manual, section 9 (that's the kernel-functions girlies ✨), and it's literally the function that goes and asks a processor what nap positions it's got available. iconic behaviour honestly.

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✨ NAME ✨

acpi_processor_evaluate_cst — evaluate the processor _CST control method. that's it, that's the whole vibe 🎀

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🌸 SYNOPSIS 🌸

int acpi_processor_evaluate_cst(acpi_handle handle, u32 cpu,
                                struct acpi_processor_power *info);

so you hand it three things and it hands you back an int. slay.

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🦋 ARGUMENTS 🦋

• handle — the ACPI handle of the processor object that's holding the _CST. like, the house where the C-state info lives 🏠
• cpu — the numeric ID of the target CPU. yes it's just a number, no it's not optional, it's giving "which sibling are we talking about" energy 🙈
• info — the object you want the C-states information written into. it's the little container that gets filled up 🫶

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👑 DESCRIPTION 👑

so what it does is: it extracts the C-state information for the given CPU out of the output of the _CST control method that lives under the corresponding ACPI processor object (or processor device object, same energy) and then populates info with it. literally fills it in for you, no cap ✨

and then — and this is the part where it gets kind of main character — if any ACPI_ADR_SPACE_FIXED_HARDWARE C-states show up in there, it invokes acpi_processor_ffh_cstate_probe to verify them, and updates the cpu_cstate_entry data for cpu. so it's not just copying, it's checking and updating. highkey thorough 💅

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🔥 SEE ALSO 🔥

• Kernel file ./drivers/acpi/acpi_processor.c
• acpi_processor_claim_cst_control(9)
• combine_lpi_states(9)

go read the whole family, iykyk 🌈

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fr fr if you're poking at CPU idle states in ACPI land, this is your girl. take the info struct seriously — she's writing into it 💖

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that's the whole page, bestie!! 🎀 this cutie came out of ./drivers/acpi and it's dated October 2026 — mwah, catch you on the next one 🦋💜