Updated: 2022/Sep/29
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DRM(4) Device Drivers Manual DRM(4)
NAME
drm - Direct Rendering Manager -- display configuration and graphics
rendering acceleration
SYNOPSIS
Kernel mode-setting drivers
amdgpu* at pci? dev ? function ?
i915drmkms* at pci? dev ? function ?
nouveau* at pci? dev ? function ?
radeon* at pci? dev ? function ?
rkdrm* at fdt? pass 5
sunxidrm* at fdt? pass 5
tegradrm* at fdt? pass 5
Legacy user mode-setting options and drivers
options DRM_LEGACY
viadrmums* at drm?
Options
options DRM_MAX_RESOLUTION_HORIZONTAL=integer
options DRM_MAX_RESOLUTION_VERTICAL=integer
DESCRIPTION
The Direct Rendering Manager is part of the Direct Rendering
Infrastructure for supporting display configuration and hardware
acceleration for graphics rendering and other computation on a graphics
processing unit (GPU).
drm drivers come in two generations:
Kernel mode-setting (KMS)
Modern drivers that query and control display configuration
in the kernel via ioctl(2) commands exposed to userland.
The /dev/dri/render* device nodes provide access to
graphics buffers and command stream submission for
rendering. The /dev/dri/card* device nodes additionally
provide access to the display configuration.
KMS drivers provided as modules must generally be loaded by
the bootloader, configured in boot.cfg(8), and cannot be
loaded dynamically.
User mode-setting (UMS)
Legacy drivers that rely on userland support code that
accesses device registers in the X(7) server to query and
control display configuration. The kernel may be unable to
recover if the display server crashes, or the device is
suspended or resumed.
The kernel driver and /dev/dri/card* interfaces only manage
buffers mapped in the GPU address space. Display
configuration from userland requires the INSECURE option
(see options(4)) to allow userland access to device
registers.
The DRM_LEGACY option allows legacy UMS drivers to be
loaded as modules (see module(7)).
The drm drivers provide support for the following graphics devices:
amdgpu Newer AMD graphics devices.
i915drmkms Intel integrated graphics devices from the i915 series
onward. (Some i8xx support is included but not well-
maintained. i7xx is not supported.)
nouveau NVIDIA graphics devices.
radeon Older AMD (including formerly ATI) Radeon graphics
devices.
viadrmums (legacy UMS)
VIA graphics devices.
With some drivers (at least radeon(4)), in some cases the driver does not
choose the resolution correctly. The options
DRM_MAX_RESOLUTION_HORIZONTAL and DRM_MAX_RESOLUTION_VERTICAL allow
limiting the maximum resolution in X and Y direction.
X(7) will attempt to create the device nodes automatically and use drm
automatically. To create a device node manually:
mkdir -p /dev/dri
mknod /dev/dri/card0 c 180 0
chgrp wheel /dev/dri/card0
chmod 0660 /dev/dri/card0
Debugging output can be enabled and disabled by setting flag bits in the
sysctl(8) node hw.drm2.__drm_debug. Various other knobs may be available
under hw.drm2.
FILES
/dev/dri/render* Provides access to graphics buffers and command
stream submission for rendering. Generally
unprivileged.
/dev/dri/card* In addition to everything provided by
/dev/dri/render*, provides access to change the
display configuration. Usually privileged.
CODE REFERENCES
The drm subsystem and drivers mostly live under sys/external/bsd/drm2,
with various Linux API shims in sys/external/bsd/common and some
individual drm drivers scattered elsewhere in the tree.
SEE ALSO
Xorg(1), agp(4), xorg.conf(5), X(7)
Direct Rendering Infrastructure: https://dri.freedesktop.org/
HISTORY
drm was first available for Linux and later ported to FreeBSD and NetBSD.
The port to NetBSD was redone after the introduction of KMS.
The first generation of drm drivers appeared in NetBSD 5.0. The second
generation of drm with KMS appeared in NetBSD 7.0.
AUTHORS
Too many to list.
Work on the NetBSD port was contributed by: Anonymous, Nia Alarie, Eric
Anholt, Rafal Boni, Taylor R Campbell, Mihai Chelaru, David Brownlee,
Jarom'ir Doleek, Matthias Drochner, Christoph Egger, FUKAUMI Naoki, Paul
Goyette, matthew green, Yorick Hardy, Nick Hudson, Martin Husemann, Arto
Huusko, Thomas Klausner, Jonathan Kollasch, Tonnerre Lombard, Jared
McNeill, Jeremy Morse, Kimihiro Nonaka, Tobias Nygren, Rin Okuyama, Maya
Rashish, Erik Reid, Masanobu SAITOH, Blair Sadewitz, Chuck Silvers,
Nathanial Sloss, J"org Sonnenberger, Gr'egoire Sutre, Matt Thomas, Izumi
Tsutsui, Patrick Welche, and Christos Zoulas.
CAVEATS
drm is large and complicated and has no shortage of bugs. On systems
where graphics is not important, you may wish to use userconf(4) to
disable the special-purpose drm drivers for your graphics device and fall
back to vga(4) or genfb(4) with the default display configuration
provided by firmware.
drm is not `Digital Rights Management' and does not deprive you of agency
over your own computer, except insofar as the code base is difficult to
maintain.
NetBSD 10.99 October 21, 2023 NetBSD 10.99