XDMA(4)

okay so bestie, welcome to XDMA(4) — the kernel interfaces manual page that’s about to become your new hyperfixation 💅✨. This is the DMA abstraction layer, and we’re gonna walk through it together, no cap.

🎀 NAME 🎀

xdma — DMA abstraction layer. That’s it, that’s the vibe: it’s the layer that abstracts DMA stuff so drivers don’t have to rawdog the hardware 😌.

✨ SYNOPSIS ✨

To compile xDMA device support into the kernel, put this line in your kernel configuration file:

device xdma

To compile the xDMA FDT-based test driver, also add this line:

device xdma_test

💖 DESCRIPTION 💖

xDMA is a DMA framework designed to abstract the interaction between device drivers and DMA engines. It’s giving “middle manager for memory transfers” and honestly? Iconic.

xDMA defines an interface for efficient interaction between the device driver and DMA controller. The xdma device provides a virtual DMA controller and virtual channels called xchans. The controller provides virtual channels management (allocation, deallocation, configuration) and interrupt notification establishment needed to receive events from the hardware DMA controller. So yes, it’s handling the allocation girlypop era, the deallocation era, and the configuration era, plus the interrupt notifications so you actually hear from the hardware DMA controller 🔔.

xDMA supports the following transfer types:

• Cyclic — a non-stop periodic transfer designed for applications like audio. It just keeps going and going, like your favorite playlist on repeat 🎧.
• Memcpy — a memory-to-memory transfer. Basically copy-paste but for memory, and way more legit.

👀 SEE ALSO 👀

• bus_dma(9) — the other DMA manual you should absolutely check out, bestie 🫶.

🦋 HISTORY 🦋

Support for xDMA first appeared in FreeBSD 12.0. A whole era, honestly.

👑 AUTHORS 👑

The FreeBSD xDMA framework was first added by Ruslan Bukin <br@FreeBSD.org>. Give them their flowers 💐.

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and that’s the tea ☕ — this page is from Debian, dated December 12, 2016, so shoutout to that edition and mwah 💋✨.