[Bug 294792] drm(4)

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294792

            Bug ID: 294792
           Summary: drm(4)
           Product: Documentation
           Version: Latest
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: Manual Pages
          Assignee: [email protected]
          Reporter: [email protected]
                CC: [email protected]
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drm(4) manpage

Summary: drm(4) manual page
===========================

What drm(4) documents
----------------------
drm(4) documents the Direct Rendering Manager (DRM) kernel subsystem,
implemented in FreeBSD as the drm2 driver (device drm2 in the kernel
config).  DRM is the kernel-side component of the Direct Rendering
Infrastructure (DRI) used by Mesa and other userspace graphics stacks to
submit GPU workloads without a round-trip through a display server.

The page covers:

  - What the DRM subsystem is and its role in GPU access management
  - DRM master vs. authenticated render client access model
  - Translation Table Manager (TTM) for GPU buffer object management
  - Vertical blanking (vblank) interrupt tracking and page-flip sync
  - Kernel Mode Setting (KMS) for in-kernel display configuration
  - The three /dev/dri/ device node types:
      /dev/dri/cardN      Primary node (master + authenticated clients)
      /dev/dri/renderDN   Render node (unprivileged render-only access)
      /dev/dri/controlDN  Control node (modesetting control)
  - The hw.dri sysctl tree exposed by the subsystem:
      hw.dri.debug, hw.dri.notyet, hw.dri.vblankoffdelay,
      hw.dri.timestamp_precision, and per-GPU nodes (name, vm,
      clients, bufs, vblank)

Why it was missing
-------------------
The FreeBSD src tree contains GPU-specific man pages for individual
hardware drivers (e.g., virtio_gpu(4)) but has no page documenting the
DRM core itself — the shared infrastructure that all GPU drivers build
on.  Without drm(4), there is no canonical reference for:

  - The /dev/dri/ device node layout and what each node is for
  - The DRM master / render client authentication model
  - The hw.dri sysctl namespace
  - The kernel config option (device drm2) needed to enable the subsystem

Users and driver authors currently have no FreeBSD man page to consult
for these fundamentals.  drm(4) fills that gap.

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