drm(7)

💖 drm — Direct Rendering Manager 💖

ok so bestie, welcome to the drm(7) manual page — this is the Direct Rendering Manager one, and it's genuinely iconic because it's literally the framework that runs your GPU. yes, that GPU. the one doing your games and your blender renders while you're not looking. let's get into it ✨

---

🎀 SYNOPSIS 🎀

#include <xf86drm.h>

that's it. that's the whole synopsis. slay 💅

---

🌸 DESCRIPTION 🌸

okay so the Direct Rendering Manager (DRM) is a whole framework for managing Graphics Processing Units (GPUs) 👑. it's designed to support the needs of complex graphics devices — the kind that usually contain programmable pipelines that are well suited to 3D graphics acceleration. and like, that's not even all of it: it's also responsible for memory management, interrupt handling, and DMA, all so it can provide a uniform interface to applications. main character energy fr fr.

back in the earlier days, the kernel framework was solely used to provide raw hardware access to privileged user-space processes — the ones that implement all the hardware abstraction layers. but more and more tasks got moved into the kernel over time (the way that happens 😭). all of these interfaces are based on ioctl(2) commands on the DRM character device. the libdrm library provides wrappers for these system-calls plus a ton of helpers to simplify the API. we love a helpful library 🫶

when a GPU is detected, the DRM system loads a driver for the detected hardware type. each connected GPU is then presented to user-space via a character-device that's usually available as /dev/dri/card0 and can be accessed with open(2) and close(2) ⭐. however — and this is important — it still depends on the graphics driver which interfaces are actually available on these devices. if an interface isn't available, the syscalls will fail with EINVAL. so like, vibe check your driver first 💀

🔐 Authentication 🔐

all DRM devices provide authentication mechanisms. only a DRM master is allowed to perform mode-setting or modify core state, and only one user can be DRM master at a time — there can only be one main character, sorry 🤷‍♀️. see drmSetMaster(3) for info on how to become DRM master and what the limitations are. other DRM users can be authenticated to the DRM-Master via drmAuthMagic(3) so they can perform buffer allocations and rendering. teamwork makes the dream work 🦋

🖥️ Mode-Setting 🖥️

managing connected monitors and displays and changing the current modes is called Mode-Setting. this is restricted to the current DRM master. historically this was implemented in user-space, but new DRM drivers implement a kernel interface to perform mode-setting called Kernel Mode Setting (KMS). if your hardware-driver supports it, you can use the KMS API provided by DRM — and that includes allocating framebuffers, selecting modes, and managing CRTCs and encoders. see drm-kms(7) for more ✨

🧠 Memory Management 🧠

the most sophisticated task for GPUs today is managing memory objects. textures, framebuffers, command-buffers and all other kinds of commands for the GPU have to be stored in memory. the DRM driver takes care of managing all memory objects, flushing caches, synchronizing access, and providing CPU access to GPU memory 🔥. all memory management is hardware driver dependent — however, two generic frameworks are available that most DRM drivers use:

• the Translation Table Manager (TTM)
• the Graphics Execution Manager (GEM)

they provide generic APIs to create, destroy and access buffers from user-space. but ngl, there are still many differences between the drivers so driver-dependent code is still needed 😭. many helpers are provided in libgbm (Graphics Buffer Manager) from the Mesa project. for more info on DRM memory management, see drm-memory(7) 💜

---

🙈 REPORTING BUGS 🙈

bugs in this manual should be reported to <https://gitlab.freedesktop.org/mesa/libdrm/-/issues>. please do, bestie, the maintainers want to know 🫶

---

👀 SEE ALSO 👀

• drm-kms(7)
• drm-memory(7)
• drmSetMaster(3)
• drmAuthMagic(3)
• drmAvailable(3)
• drmOpen(3)

---

and that's the page!! this one came from the Mesa/libdrm corner of the world and the date on it is September 2012 — vintage, honestly. go forth and render, bestie 🌈💅🎀