to_hpa(9)

📦 version 7.3.1, in nixpkgs unstable

💫 to_hpa(9) — the Kernel API Manual glow-up 💫

okay bestie, gather round, because we're doing math today ✨ this little icon lives in the Kernel API Manual, and its whole job is literally just: calculate an HPA offset from a DPA offset and position. that's it. that's the gig. no cap. 🎀

🌸 NAME 🌸

to_hpa — calculate an HPA offset from a DPA offset and position 💅

🦋 SYNOPSIS 🦋

u64 to_hpa (u64 dpa_offset , int pos , u8 r_eiw , u16 r_eig , u8 hb_ways
, u8 math );

look at her. six arguments. main character energy fr fr 👑

✨ ARGUMENTS ✨

okay so the original is very mysterious about these and honestly? we respect the privacy. every single one is listed as "-- undescribed --" and we are NOT going to make stuff up, so here's the full roster, untouched, exactly as the page gives them:

  • dpa_offset — -- undescribed -- 🙈
  • pos — -- undescribed -- 🙈
  • r_eiw — -- undescribed -- 🙈
  • r_eig — -- undescribed -- 🙈
  • hb_ways — -- undescribed -- 🙈
  • math — -- undescribed -- 🙈
ngl the arguments section is giving "no thoughts, head empty" but that's literally what the manpage says, so we're keeping it 💀 (the description below spills the tea though — keep reading 🫶)

💖 DESCRIPTION 💖

here's the actual lore, laid out one parameter at a time, because the original does it in one long run-on line and we're being nice to your eyeballs:

  • dpa_offset: device physical address offset
  • pos: devices position in interleave
  • r_eiw: region encoded interleave ways
  • r_eig: region encoded interleave granularity
  • hb_ways: host bridge interleave ways
  • math: interleave arithmetic (MODULO_MATH or XOR_MATH)

so you feed her a DPA offset, a position in the interleave, the region's encoded interleave ways and granularity, the host bridge interleave ways, and which flavor of interleave arithmetic you're vibing with — MODULO_MATH or XOR_MATH — and she does her thing. iconic. 🧚

🔥 RETURN 🔥

host physical address offset 🫶 (that's the u64, bestie, that's the whole point)

🌈 SEE ALSO 🌈

go touch some more kernel grass, these are all right here in the kernel file ./tools/testing/cxl/test/cxl_translate.c:

iykyk 👑

so yeah — that's to_hpa(9), short and sweet and absolutely slaying in the CXL test tooling ✨ big thanks to the ./tools/testing/cxl/test source for bringing us this baddie, dated October 2026. mwah 💋 go translate some addresses, bestie 💜

📦 where this page comes from