Direct Rendering Infrastructure

DRI-1.0

Original author(s)	Precision Insight, Tungsten Graphics
Developer(s)	freedesktop.org
Initial release	August 1998 (1998-08)
Stable release	2.4.x / February 2009
Development status	maintained, marked for obsoletion
Written in	C
Platform	POSIX
Type	Framework / API
License	MIT and other licenses
Website	dri.freedesktop.org

DRI-2.0

Original author(s)	various
Developer(s)	freedesktop.org
Initial release	September 4, 2008 (2008-09-04)
Stable release	2.4.x / February 2009 (2009-02)
Development status	active
Written in	C
Platform	POSIX
Type	Framework / API
License	MIT and other licenses
Website	dri.freedesktop.org

DRI-3.0

Original author(s)	Keith Packard et al.
Developer(s)	freedesktop.org
Initial release	November 1, 2013 (2013-11-01)
Stable release	November 1, 2013 (2013-11-01) / 3.0
Development status	active
Written in	C
Platform	POSIX
Type	Framework / API
License	MIT and other licenses
Website	dri.freedesktop.org

There are two graphics hardware drivers: one resides inside of the X display server. There have been several designs of this driver. The current one splits it in two portions: DIX (Device-Independent X) and DDX (Device-Dependent X)

Glamor will simplify the X server, and libGL-fglrx-glx could use the libDRM of the radeon open-source driver instead of the proprietary binary blob.

Rendering calculations are outsourced over OpenGL to the GPU to be done in real-time. The DRI regulates access and book-keeping.

The Direct Rendering Infrastructure (DRI) is a framework for allowing direct access to graphics hardware under the X Window System in a safe, efficient way. The main use of DRI is to provide hardware acceleration for the Mesa implementation of OpenGL. DRI has also been adapted to provide OpenGL acceleration on a framebuffer console without a display server running.

DRI implementation is scattered through the X Server and its associated client libraries, Mesa 3D and the Direct Rendering Manager kernel subsystem. All of its source code is free software.

Software architecture

Direct Rendering Infrastructure is intended to facilitate the acceleration of 3D rendering and General-purpose computing on graphics processing units on available hardware by the operating system.

The DRI is split into three parts:

• the Direct Rendering Manager (DRM), a kernel component, for command checking and queuing (not scheduling); the DRM is a combination of at least two kernel modules, one of core DRM code and others providing APIs to userland to access different classes of video hardware.
  • KMS driver, the device driver for the display controller
  • Graphics Execution Manager (GEM) or gemified Translation Table Maps (TTM), a kernel component, that despite its name, it does not execute anything but is responsible for the memory management of the graphics memory;
• the Mesa 3D device drivers, a userspace component, that does the translation of OpenGL commands into hardware specific commands; it prepares buffers of commands to be sent to the hardware by the DRM and interacts with the windowing system for synchronization of access to the hardware

The hardware specific library libdrm implements the userspace interface to the kernel DRM. Libdrm contains a full set of functions to obtain information about encoders, connectors (such as DAC, TMDS, LVDS, etc.) and CRTC, such as their current state, their combinations, connector properties and available modes.

Additional code provides access to the API provided by the driver module. In X this is the libdri.so support module and a DRI-enabled DDX (2D driver). In the framebuffer implementation this is MiniGLX, which initializes the DRM and provides some X APIs to the userspace driver despite the lack of a display server.

There is also a project using the Linux kernel DRI to gain direct access to the hardware for the purpose of using it as General-purpose computing on graphics processing units.

• https://github.com/migle/gpgpu-dri
• Fastra II

Adoption

Several open source DRI drivers have been written, including ones for ATI Mach64, ATI Rage128, ATI Radeon, 3dfx Voodoo3 through Voodoo5, Matrox G200 through G400, SiS 300-series, Intel i810 through i965, S3 Savage, VIA UniChrome graphics chipsets, and nouveau for Nvidia. Some graphics vendors have written closed-source DRI drivers, including ATI and Kyro.

The various versions of DRI have been implemented by various operating systems, amongst others by the Linux kernel, FreeBSD, NetBSD, OpenBSD, and OpenSolaris.

DRI1

• single shared back buffer for screen
• applications clip to back buffer area
• DRI application block X
• only temporary allocations possible in graphics memory

DRI2

Work on DRI2 started at the 2007 X Developers' Summit. The new rendering infrastructure improves several shortcomings of the old design, including removing internal locks and adding proper support for off-screen rendering, so that compositing and XVideo/OpenGL applications are properly managed.

• per-window stencil-/depth-/back-buffers
• shared across applications (as required by GLX)
• allocated from X
• objects passed by global GEM handles (huge security issues)

DRI3

Due to several limitations of DRI2, a new extension called DRI-Next was proposed by Keith Packard and Eric Anholt at the X.Org Developer's Conference 2012. The extension was proposed again as DRI3000 at Linux.conf.au 2013. DRI3 revolves around using POSIX file descriptors for passing kernel objects between the display server and the application instead of passing global GEM handles. As part of the proposed DRI3 is also the Present (formerly Swap) extension for swapping the screen contents in a synchronized manner. DRI3 improves the window resizing process, improves security a bit, utilizes DMA_BUF.

• client-allocated per-windows buffers (this is how "Wayland does it")
• no sharing at all (sharing is required by GLX)
• allocated and managed by client
• file descriptor (FD) passing by

DMA buffer sharing has been available since Linux kernel 3.3

DRI3 extension

• provides access to DRM device
• share DRM pixel buffers between client and server
• share buffer idle semaphore (futex) between client and server

Present extension

• copy or flip pixmap to window
• synchronize with vblank
• deliver events when present occurs

History

The project was started by Jens Owen and Kevin E. Martin of Precision Insight. It was first made widely available as part of XFree86 4.0 and is now part of the X.Org Server. It is currently maintained by the free software community.

• 

  2D drivers inside of the X server

• 

  Indirect rendering over GLX, using Utah GLX; separate: fbdev

• 

  Early DRI: Mode setting is still being performed by the X display server, which forces it to be run as root

• 

  Finally all access goes through the Direct Rendering Manager

• 

  In Linux kernel 3.12 render nodes were introduced; DRM and the KMS driver were split. Wayland implements direct rendering over EGL

See also

• Mesa (computer graphics)
• Gallium3D
• DirectFB

References

• A Multipipe Direct Rendering Architecture for 3D (Jens Owen and Kevin Martin, 1998) (original DRI design document)
• Direct Rendering Infrastructure, Low-Level Design Document (Kevin E. Martin, Rickard E. Faith, Jens Owen, and Allen Akin, 1999)
• DRI Extension for supporting Direct Rendering Protocol Specification (Jens Owen and Kevin Martin, Precision Insight, 1999)
• DRI for beginners (Frank Worsley)
• Getting X Off The Hardware (Keith Packard)
• DRI - Developer interview with Owain Ainsworth (OpenBSD Journal)
• The DRI3 Extension Version 1.0 (Keith Packard, 2013)

External links

• Direct Rendering Infrastructure project home page
• Direct Rendering Infrastructure project "To Do" page