111 lines
3.6 KiB
Groff
111 lines
3.6 KiB
Groff
.\" automatically generated with
|
|
.\" docbook2mdoc drm.xml > drm.7
|
|
.Dd September 2012
|
|
.Dt DRM 7
|
|
.Os
|
|
.Sh NAME
|
|
.Nm drm
|
|
.Nd Direct Rendering Manager
|
|
.Sh SYNOPSIS
|
|
.Fd #include <xf86drm.h>
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Em Direct Rendering Manager
|
|
(DRM) is a framework
|
|
to manage
|
|
.Em Graphics Processing Units
|
|
(GPUs). It is
|
|
designed to support the needs of complex graphics devices, usually
|
|
containing programmable pipelines well suited to 3D graphics
|
|
acceleration. Furthermore, it is responsible for memory management,
|
|
interrupt handling and DMA to provide a uniform interface to
|
|
applications.
|
|
.Pp
|
|
In earlier days, the kernel framework was solely used to provide raw
|
|
hardware access to privileged user-space processes which implement
|
|
all the hardware abstraction layers. But more and more tasks were
|
|
moved into the kernel. All these interfaces are based on
|
|
.Xr ioctl 2
|
|
commands on the DRM character device. The
|
|
.Em libdrm
|
|
library provides wrappers for these system-calls and many helpers to
|
|
simplify the API.
|
|
.Pp
|
|
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 is usually available as
|
|
.Pa /dev/dri/card0
|
|
and can be accessed with
|
|
.Xr open 2
|
|
and
|
|
.Xr close 2 .
|
|
However, it still depends on the graphics driver which interfaces are
|
|
available on these devices. If an interface is not available, the
|
|
syscalls will fail with
|
|
.Ql EINVAL .
|
|
.Ss 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. See
|
|
.Xr drmSetMaster 3
|
|
for information on how to become DRM-Master and what the limitations
|
|
are. Other DRM users can be authenticated to the DRM-Master via
|
|
.Xr drmAuthMagic 3
|
|
so they can perform buffer allocations and rendering.
|
|
.Ss Mode-Setting
|
|
Managing connected monitors and displays and changing the current
|
|
modes is called
|
|
.Em 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
|
|
.Em Kernel Mode Setting
|
|
(KMS). If your
|
|
hardware-driver supports it, you can use the KMS API provided by
|
|
DRM. This includes allocating framebuffers, selecting modes and
|
|
managing CRTCs and encoders. See
|
|
.Xr drm-kms 7
|
|
for more.
|
|
.Ss Memory Management
|
|
The most sophisticated tasks 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 are used by most DRM drivers. These
|
|
are the
|
|
.Em Translation Table Manager
|
|
(TTM) and the
|
|
.Em Graphics Execution Manager
|
|
(GEM). They provide
|
|
generic APIs to create, destroy and access buffers from user-space.
|
|
However, there are still many differences between the drivers so
|
|
driver-depedent code is still needed. Many helpers are provided in
|
|
.Em libgbm
|
|
(Graphics Buffer Manager) from the
|
|
.Em mesa-project .
|
|
For more information on DRM
|
|
memory-management, see
|
|
.Xr drm-memory 7 .
|
|
.Sh REPORTING BUGS
|
|
Bugs in this manual should be reported to
|
|
https://bugs.freedesktop.org/enter_bug.cgi?product=DRI&component=libdrm
|
|
under the "DRI" product, component "libdrm"
|
|
.Sh SEE ALSO
|
|
.Xr drm-kms 7 ,
|
|
.Xr drm-memory 7 ,
|
|
.Xr drmSetMaster 3 ,
|
|
.Xr drmAuthMagic 3 ,
|
|
.Xr drmAvailable 3 ,
|
|
.Xr drmOpen 3
|
|
.Sh AUTHORS
|
|
.An -nosplit
|
|
.Sy Direct Rendering Manager
|
|
.Pp
|
|
.Sy libdrm
|
|
.An -split
|
|
Developer:
|
|
.An David Herrmann Aq Mt dh.herrmann@googlemail.com
|