FIELD_PREP_WM16_CONST(9)

✨ FIELD_PREP_WM16_CONST ✨

okay bestie so this one is from the Kernel API Manual and it's literally called FIELD_PREP_WM16_CONST — say that five times fast, i dare you 💅 it's all about prepping a constant bitfield element, except the mask lives in the upper half. yes ma'am, we're fancy like that.

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🌸 SYNOPSIS 🌸

FIELD_PREP_WM16_CONST (_mask , _val );

that's it. two things in, magic out. the way that this macro just works 🫶

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🎀 ARGUMENTS 🎀

• _mask — the shifted mask that defines the field's length and its position. it's giving "i contain multitudes" ✨
• _val — the value you're putting in the field. the actual content. the main character 💖

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🦋 DESCRIPTION 🦋

so here's the tea, bestie: FIELD_PREP_WM16_CONST masks and shifts up the value, and then it bitwise ORs that result with the mask shifted up by 16. two whole jobs. iconic behavior honestly 👑

this is lowkey perfect for a super common hardware register design, where the upper 16-bit half of a 32-bit register is used as a write-enable mask 🔥 in a register like that, a bit in the lower half only gets updated if the corresponding bit in the upper half is high. like, the upper half is the bouncer at the club and it's deciding which lower-half bits get in 💀

now, the key difference: unlike FIELD_PREP_WM16, this version is a constant expression — which means it can be used in initializers 🎉 that's the slay. the tradeoff? error checking is less comfortable for this version 😭 like yeah you get the constant-expression flex but the compiler's not gonna hold your hand through it. no cap.

fr fr, bestie: constant expression = you can use it in initializers. less comfortable error checking = you're kinda on your own if something's wrong. don't come for me, that's just what the manpage says 💅

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🌈 SEE ALSO 🌈

• Kernel file ./include/linux/hw_bitfield.h
• FIELD_PREP_WM16(9)

like, go read the non-const one too, it's the sibling energy you need 🧚

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and that's the whole vibe check bestie 💜 this page came to you from ./include/linux and it's dated October 2026 — so yeah, future-flavored kernel lore, stay hydrated, go prep your bitfields, and remember: upper half = mask, lower half = value, and the constant expression is the moment 👑✨🍓