Direct Rendering Infrastructure

DRI-1.0

Original author(s)	Precision Insight, Tungsten Graphics
Developer(s)	freedesktop.org
Initial release	August 1998[1]
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[2]
Website	dri.freedesktop.org

DRI-2.0

Original author(s)	Kristian Høgsberg et al.
Developer(s)	freedesktop.org
Initial release	September 4, 2008[3]
Stable release	2.8 / July 11, 2012[4]
Development status	active
Written in	C
Platform	POSIX
Type	Framework / API
License	MIT and other licenses[2]
Website	dri.freedesktop.org

DRI-3.0

Original author(s)	Keith Packard et al.
Developer(s)	freedesktop.org
Initial release	November 1, 2013[5]
Stable release	1.0 / November 1, 2013[5]
Development status	active
Written in	C
Platform	POSIX
Type	Framework / API
License	MIT and other licenses[2]
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.^[6] 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.
  • CRTC, CRT-controller, the device driver for the display controller is part of DRM; it offers the KMS API to user-space application to do mode-setting
  • 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.^[7]

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^[8]
• applications clip to back buffer area
• DRI application block X
• only temporary allocations possible in graphics memory

DRI2

The new rendering infrastructure improves several shortcomings of the old design, including removing internal locks and adding proper support for off-screen rendering,^[8] so that compositing and XVideo/OpenGL applications are properly managed.^[9]

• per-window stencil-/depth-/back-buffers^[8]
• shared across applications (as required by GLX)
• allocated from X
• objects passed by global GEM handles (huge security issues)

DRI3

DRI3 revolves around using POSIX file descriptors for passing kernel objects between the display server and the application^[10] 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.^[11] DRI3 improves the window resizing process, improves security a bit, utilizes DMA_BUF.^[12][13]

• 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^[14]

DMA buffer sharing has been available since Linux kernel 3.3^[15]

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 from Precision Insight (funded by Silicon Graphics and Red Hat).^[1][16] It was first made widely available as part of XFree86 4.0^[1][17] and is now part of the X.Org Server. It is currently maintained by the free software community.

Work on DRI2 started at the 2007 X Developers' Summit from a Kristian Høgsberg's proposal.^[18][19] Høgsberg himself wrote the new DRI2 extension and the modifications to Mesa and GLX.^[20] In March 2012 DRI2 was mostly done,^[21][22][9] but it couldn't make into X.Org Server version 1.5^[23] and had to wait until version 1.6 from February 2009.^[24] The DRI2 extension was officially included in the X11R7.5 release of October 2009.^[25] The first public version of the DRI2 protocol (2.0) was announced in April 2009.^[26] Since then there has been several revisions, being the most recent the version 2.8 from July 2012.^[4]

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.^[27] The extension was proposed again as DRI3000 at Linux.conf.au 2013.^[28][12] DRI3 and Present extensions were developed during 2013 and merged into the X.Org Server 1.15 release from December 2013.^[29][30] The first and only version of the DRI3 protocol (1.0) was released in November 2013.^[5]

• 

  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

Notes

1. Owen, Jens. "The DRI project history". DRI project wiki. Retrieved 16 April 2016.
2. Mesa DRI License / Copyright Information - The Mesa 3D Graphics Library
3. Høgsberg, Kristian (4 September 2008). "The DRI2 Extension - Version 2.0". X.Org. Retrieved 20 April 2016.
4. Airlie, Dave (11 July 2012). "[ANNOUNCE] dri2proto 2.8". xorg-announce (Mailing list).
5. Packard, Keith (1 November 2013). "[ANNOUNCE] dri3proto 1.0". xorg-announce (Mailing list).
6. "Mesa 3D and Direct Rendering Infrastructure wiki". Retrieved 15 July 2014.
7. Michael Larabel (16 June 2010). "Talking About Kernel Mode-Setting". Retrieved 2015-03-07.
8. Packard, Keith (21 July 2008). "X output status july 2008". Retrieved 20 April 2016.
9. Høgsberg, Kristian (31 March 2008). "DRI2 Direct Rendering". Retrieved 20 April 2016.
10. Packard, Keith (5 October 2012). "FD passing for DRI.Next". Retrieved 16 April 2016.
11. Edge, Jake (9 October 2013). "DRI3 and Present". LWN.net. Retrieved 4 May 2016.
12. Packard, Keith (19 February 2013). "DRI3000 — Even Better Direct Rendering". Retrieved 16 April 2016.
13. Packard, Keith (4 June 2013). "Completing the DRI3 Extension". Retrieved 16 April 2016.
14. Semwal, Sumit. "DMA Buffer Sharing API Guide". Kernel.org. Retrieved 16 April 2016.
15. Corbet, Jonathan (11 January 2012). "DMA buffer sharing in 3.3". LWN.net. Retrieved 16 April 2016.
16. Owen, Jens; Martin, Kevin E. (15 September 1998). "A Multipipe Direct Rendering Architecture for 3D". Retrieved 16 April 2016.
17. "Release Notes for XFree86 4.0". XFree86 Project. 7 March 2000. Retrieved 16 April 2016.
18. "X Developers' Summit 2007 - Notes". X.Org. Retrieved 7 March 2016.
19. Høgsberg, Kristian (3 October 2007). "DRI2 Design Wiki Page". xorg (Mailing list).
20. Høgsberg, Kristian (4 February 2008). "Plans for merging DRI2 work". xorg (Mailing list).
21. Høgsberg, Kristian (15 February 2008). "DRI2 committed". xorg (Mailing list).
22. Høgsberg, Kristian (31 March 2008). "DRI2 direct rendering". xorg (Mailing list).
23. Høgsberg, Kristian (4 August 2008). "Backing out DRI2 from server 1.5". xorg (Mailing list).
24. "Server 1.6 branch". X.org. Retrieved 7 February 2015.
25. "Release Notes for X11R7.5". X.Org. Retrieved 20 April 2016.
26. Høgsberg, Kristian (20 April 2009). "[ANNOUNCE] dri2proto 2.0". xorg-announce (Mailing list).
27. Packard, Keith (28 September 2012). "Thoughts about DRI.Next". Retrieved 16 April 2016.
28. Willis, Nathan (11 February 2013). "LCA: The X-men speak". LWN.net. Retrieved 26 February 2016.
29. Packard, Keith. "[ANNOUNCE] xorg-server 1.14.99.901". X.org. Retrieved 9 February 2015.
30. Larabel, Michael. "X.Org Server 1.15 Release Has Several New Features". Phoronix. Retrieved 9 February 2015.

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