check_acpi_cpu_flag(9)

💅 check_acpi_cpu_flag(9) — the kernel API manual, bestie edition 🎀

okay so this is a page from the Kernel API Manual, and the star of the show is check_acpi_cpu_flag(9). she's a little function, she answers one question, and she ate. periodt. ✨

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🌸 NAME 🌸

check_acpi_cpu_flag — Determine if CPU node has a flag set

like, literally just checking whether a CPU node's got a specific flag turned on. that's the whole vibe check. 💖

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🦋 SYNOPSIS 🦋

int check_acpi_cpu_flag (unsigned int cpu , int rev , u32 flag );

three arguments, all passed in, no cap. 🫶

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🍓 ARGUMENTS 🍓

• cpu — Kernel logical CPU number. which CPU are we talking about, bestie? this one. 🔥
• rev — The minimum PPTT revision defining the flag. i.e. the flag only exists from this PPTT revision onward — if the table's too old, it's giving ✨nothing✨.
• flag — The flag itself. the actual thing you're checking for. iconic.

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💜 DESCRIPTION 💜

Check the node representing a CPU for a given flag.

that's it. that's the whole description. she's concise, she's efficient, she's main character energy. 🌈 you hand her a CPU, a minimum PPTT revision, and a flag, and she goes and looks at the node representing that CPU to see if the flag's set. lowkey obsessed with how simple this is. 💅

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⭐ RETURN ⭐

so here's what you get back — and ngl, the returns are a whole personality:

• -ENOENT — returned if any of these lil situations happen:
  • can't get the CPU's ACPI Processor UID 😭
  • the PPTT doesn't exist 🙈
  • the CPU cannot be found 💀
  • the table revision isn't new enough 👑
• 1 — any passed flag set. slay, the flag is on. 🔥
• 0 — flag unset. no flag, no problem. 💖

bestie pls note: that negative -ENOENT is a real error code, not a count. don't go treating it like a number of flags, i'm begging. 😭

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🌟 SEE ALSO 🌟

the kernel file lives at ./drivers/acpi/pptt.c — that's the home base, iykyk. 🎀

and here's the whole friend group, all in (9):

• acpi_pptt_walk_cache(9)
• acpi_count_levels(9)
• acpi_pptt_leaf_node(9)
• acpi_find_processor_node(9)
• update_cache_properties(9)
• topology_get_acpi_cpu_tag(9)
• acpi_get_cache_info(9)
• cache_setup_acpi(9)
• acpi_pptt_cpu_is_thread(9)
• find_acpi_cpu_topology(9)
• find_acpi_cpu_topology_package(9)
• find_acpi_cpu_topology_cluster(9)
• find_acpi_cpu_topology_hetero_id(9)
• acpi_pptt_get_child_cpus(9)
• acpi_pptt_get_cpus_from_container(9)
• find_acpi_cache_level_from_id(9)
• acpi_pptt_get_cpumask_from_cache_id(9)

go read them. they're all serving. 🧚💜

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and that's the page, bestie!! 🫶 this whole thing ships out of ./drivers/acpi, dated October 2026, and it's filed under check_acpi_cpu_flag(9) — so if you ever forget where you read it, that's the ⭐ header ⭐ right there. bye bye, go check those flags, mwah 💋🌸