dma_mmap_from_dev_coherent(9)

💅 dma_mmap_from_dev_coherent — like, the Kernel API Manual page you didn't know you needed

okay bestie, gather round, because today we're talking about dma_mmap_from_dev_coherent(9) and honestly? she's a little niche but she serves. this is the Kernel API Manual entry, so you know it's the real deal ✨

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🌸 NAME 🌸

dma_mmap_from_dev_coherent — mmap memory from the device coherent pool 🫶

like literally, it maps memory out of the per-device coherent pool. that's the whole vibe.

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✨ SYNOPSIS ✨

int dma_mmap_from_dev_coherent (struct device *dev , struct
vm_area_struct *vma , void *vaddr , size_t size , int *ret );

five arguments, one int coming back at you. slay. no cap, that's the signature, don't @ me 💅

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🎀 ARGUMENTS 🎀

• dev — the device from which the memory was allocated 👑
• vma — the vm_area for the userspace memory 🌸
• vaddr — the cpu address returned by dma_alloc_from_dev_coherent ⭐
• size — size of the memory buffer allocated 📏
• ret — result from remap_pfn_range 🌀

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🦋 DESCRIPTION 🦋

so what does she do. okay so: this checks whether the memory was allocated from the per-device coherent memory pool, and if so, maps that memory to the provided vma. that's it. that's the whole job. iconic behavior honestly 💖

and then the return value, which is where it gets kinda main-character:

• it returns 1 if vaddr belongs to the device coherent pool and the caller should return ret 🔥
• or 0 if they should proceed with mapping memory from generic areas 🌈

so like, 1 = "yeah babe it's ours, bail out with ret", 0 = "nope, not ours, keep it moving with the generic areas". vibe check complete ✨

fr fr read the return value carefully, bestie — 1 and 0 mean very different things for whoever's calling you, and getting them backwards is gonna be a whole situation 😭

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💜 SEE ALSO 💜

• Kernel file ./kernel/dma/coherent.c 📂
• dma_alloc_from_dev_coherent(9) 🧚
• dma_release_from_dev_coherent(9) 🍓

the whole coherent-pool friend group, honestly. go read them together, iykyk 💅

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and that's the page!! 🎉 source is ./kernel/dma, dated October 2026 — bookmark it, screenshot it, send it to your group chat, whatever you gotta do. bye bestie, go map some memory responsibly 🫶✨🎀