arch_phys_wc_add(9)

💅 arch_phys_wc_add(9) — from the Kernel API Manual, bestie

okay so picture this: you're deep in kernel land, the manual name is literally arch_phys_wc_add, and you need to know what it does. say less. i got you. 🫶

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✨ NAME ✨

arch_phys_wc_add — add a WC MTRR and handle errors if PAT is unavailable. that's the whole vibe. 💫

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🎀 SYNOPSIS 🎀

int arch_phys_wc_add (unsigned long base , unsigned long size );

like, it returns an int. remember that. it matters later, i promise. 👀

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🌸 ARGUMENTS 🌸

• base — the physical base address. where the region starts, periodt. 📍
• size — size of region. how much of it we're talking about, bestie. 📏

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💖 DESCRIPTION 💖

so here's the tea, and it's giving conditional logic. 🍵

If PAT is available, this function literally does nothing. nothing. zero. it's a no-op and it's iconic for it. 🧘

If PAT is not available, then it actually gets to work: it attempts to add a WC MTRR covering size bytes starting at base — and if that fails, it logs an error. no cap, that's it. 🚨

lowkey important: the caller should provide a power of two size on an equivalent power of two boundary. the sizes gotta line up like a perfect little grid. if they don't… bestie. ⚠️

Also, drivers must store the return value so they can pass it to mtrr_del_wc_if_needed later — but drivers should not try to interpret that return value. store it, hand it off, don't read into it. it's not that kind of return value. 🙈💅

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🦋 SEE ALSO 🦋

• Kernel file ./arch/x86/kernel/cpu/mtrr/mtrr.c 👑
• mtrr_rendezvous_handler(9)
• set_mtrr(9)
• mtrr_add_page(9)
• mtrr_add(9)
• mtrr_del_page(9)
• mtrr_del(9)
• mtrr_bp_init(9)
• mtrr_save_state(9)

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and that's the page!! 🎉 brought to you by ./arch/x86/kernel/cpu/mtrr, dated October 2026, in the arch_phys_wc_add(9) section of the Kernel API Manual. mwah. 💋✨🌈