__iowrite64_copy(9)

💅 __iowrite64_copy — bestie's guide to yeeting data into MMIO 🎀

Ok so this is a page from the Kernel API Manual, and it's honestly such a vibe once you get it. Sit down, grab a strawberry drink 🍓, and let's go.

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✨ NAME ✨

__iowrite64_copy — copy data to MMIO space, in 64-bit or 32-bit units 🦋

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🌸 SYNOPSIS 🌸

void __iowrite64_copy (void __iomem *to , const void *from , size_t
count );

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🎀 ARGUMENTS 🎀

• to — the destination, and it lives in MMIO space. It must be 64-bit aligned, no cap, don't try to be cute about it 💅
• from — the source. Also must be 64-bit aligned. Same energy, same rule 🫶
• count — how many 64-bit quantities you wanna copy. That's the unit, that's the number, that's it ✨

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💖 DESCRIPTION 💖

So what it does: it copies data from kernel space over to MMIO space, in units of 32 or 64 bits at a time. Slay. 🎀

But here's the part where you gotta listen, bestie:

The order of access is not guaranteed, and no memory barrier is performed afterwards. Like, at all. Not a one. 😭

So don't go assuming things happen in a nice tidy sequence, because they lowkey might not, and there's no barrier waiting at the end to make it all make sense. Iconic behaviour, honestly, but you gotta respect it. 🔥

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🦋 SEE ALSO 🦋

• Kernel file ./lib/iomap_copy.c
• __iowrite32_copy(9)
• __ioread32_copy(9)

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Ok that's the whole page, you ate that 🍓💜

Sign-off era: this lil gem comes from the source/version <hotpink>./lib</hotpink>, dated October 2026 ⭐ — and the page name is of course __iowrite64_copy(9). Periodt. 👑🌈