STRUCT CP_HEADER(9)

💖 struct cp_header(9) 💖

okay bestie, so this is a page from the Kernel API Manual about struct cp_header — yes the whole manual section 9, we're doing kernel internals today, slay 🎀

✨ NAME ✨

struct cp_header — the SST-CP (core-power) header, and yes it does exactly what it says on the tin 🫶

🌸 SYNOPSIS 🌸

struct cp_header {
    u64 feature_id :4;
    u64 feature_rev :8;
    u64 ratio_unit :2;
    u64 reserved :50;
 };

like, look at those bitfields. little bitty slivers of a u64. it's giving precision 💅

🦋 Members 🦋

• feature_id — the "which feature even are we" field, and the values are: 0=SST-CP, 1=SST-PP, 2=SST-BF, 3=SST-TF. pick your fighter 😤
• feature_rev — the interface version number for this SST feature. it's the vibe check for how new your interface is ⭐
• ratio_unit — frequency ratio unit. 00 means 100MHz. all others are reserved — so like, don't go inventing values, bestie 💀
• reserved — reserved for future use. it's just sitting there, 50 whole bits, waiting for its main character moment 🌈

👑 Description 👑

lowkey the whole point: this structure is used to store the SST-CP header. and it's packed to the same format as defined in the specifications — so the layout is not a suggestion, it's the spec, periodt ✨

💜 SEE ALSO 💜

Kernel file: ./drivers/platform/x86/intel/speed_select_if/isst_tpmi_core.c — that's the one, that's where it lives 🧚

and then a whole friend group of structs and friends, all linked here:

• struct sst_header(9)
• struct pp_header(9)
• struct feature_offset(9)
• struct levels_offset(9)
• struct pp_control_offset(9)
• struct pp_status_offset(9)
• struct perf_level(9)
• struct tpmi_per_power_domain_info(9)
• struct tpmi_sst_struct(9)
• struct tpmi_sst_common_struct(9)
• map_cdies(9)
• map_partition_power_domain_id(9)

okay that's the whole page, no cap 💖 this cutie came out of ./drivers/platform/x86/intel/s... (source/version, yes it's truncated like that in the footer, iconic) and it's dated October 2026, and the footer also reminds us it's all about struct cp_header(9) — bye bestie, go read some kernel source 🍓🔥