Mode setting

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Regulating access to the hardware is a fundamental kernel task. The Direct Rendering Manager and KMS are part of the Linux kernel. The KMS does only the mode setting.

Mode setting is a software operation that activates a display mode (screen resolution, color depth, and refresh rate) for a computer's display adapter.

In kernel mode-setting (KMS), the display mode is set by the kernel. In user-space mode-setting (UMS), the display mode is set by a userland process.

Kernel mode-setting is more flexible and allows displaying of an error in the case of a fatal error in the kernel, even when using a user-space display server.

User-space mode setting would have needed superuser privileges for direct hardware access, so kernel-based mode setting increases security because the user-space graphics server does not need superuser privileges.

Implementation[edit]

Microsoft Windows[edit]

Microsoft Windows versions that are NT-based use kernel mode setting. The kernel error display made possible by kernel mode setting is known as the Blue Screen of Death.

Linux[edit]

The role of KMS (Kernel mode-setting), Linux example

The Linux Graphics Stack 2013
Wayland compositors require KMS (and also OpenGL ES and EGL)
The place of certain Linux kernel modules
evdev is the Linux kernel module that receives data from various Input devices such as Keyboard, Mouse, Touch-Pad, etc. The data is passed to the Display server (e.g. the X.Org Server or some Wayland compositor only to be passed further to the wayland client respectively X client. Some applications require a minimal latency

The Linux kernel got the prerequisite for kernel-based mode setting by accepting Intel's GEM in version 2.6.28, released in December 2008.[1] This will be replaced by Tungstens Graphics TTM (Translation Table Maps) memory manager which supports the GEM API.[2] TTM was developed for the free and open-source drivers for Radeon and S3 Graphics graphic chipsets (see Free and open-source graphics device driver).[3] Support for Intel GMA graphic chipsets has been accepted in version 2.6.29 which was released on March 23, 2009.[4] Support for pre-R600 ATI Radeon graphics cards has been accepted in version 2.6.31 which was released on September 9, 2009.[5] Support for R600 and R700 was in development within DRM and has been merged in version 2.6.32.[6] Support for Evergreen (R800) has been merged in version 2.6.34. As Nvidia did not release all the needed documentation for its graphics chip, the development is under the nouveau project which uses reverse engineering to get it to work. Nouveau has been accepted in version 2.6.33 of the kernel which was released on December 10, 2009. This will allow to use kernel-based mode setting for Nvidia cards with this driver. Wayland compositors (e.g. Weston) and kmscon depend on kernel mode setting via ioctl.

FreeBSD[edit]

FreeBSD has support for both kernel-based mode setting and GEM for later generations of Intel GPUs (IronLake, SandyBridge, and IvyBridge) starting with version 9.1.[7]

OpenBSD[edit]

OpenBSD, which has a strong focus on security, is interested in getting kernel-based mode setting in order to run X without superuser privileges.[8] Support for kernel-based mode setting for later generations of Intel GPUs was added to OpenBSD in March 2013, available starting with OpenBSD 5.4 release.[9]

Alternatives[edit]

  • At the Linux Plumbers Conference 2013 it will be suggested to split GEM and KMS.[10]
  • There is the Atomic Display Framework;[11][12] it was presented by Google's Android-Team at the Linux Plumbers Conference 2013
  • There is the Common Display Framework [13]

See also[edit]

References[edit]

  1. ^ "Linux 2 6 28". Linux Kernel Newbies. Retrieved 2013-02-14. 
  2. ^ Larabel, Michael (2008-08-26). "A GEM-ified TTM Manager For Radeon". Phoronix. Retrieved 2013-02-14. 
  3. ^ Larabel, Michael (2009-06-10). "TTM Memory Manager Gets Ready For Release". Phoronix. Retrieved 2013-02-14. 
  4. ^ "Linux 2 6 29". Linux Kernel Newbies. Retrieved 2013-02-14. 
  5. ^ "Linux 2 6 31". Linux Kernel Newbies. 2009-09-09. Retrieved 2013-02-14. 
  6. ^ Larabel, Michael (2009-09-30). "AMD R600/700 2D Performance: Open vs. Closed Drivers". Phoronix. Retrieved 2013-02-14. 
  7. ^ "FreeBSD 9.1-RELEASE Release Notes". FreeBSD Foundation. 30 December 2012. 
  8. ^ Larabel, Michael (February 25, 2009). "Gallium3D, EGL Now Buildable On FreeBSD". Phoronix. Retrieved 2013-02-14. 
  9. ^ Larabel, Michael (March 18, 2013). "Intel KMS/DRM Driver Readied For OpenBSD". Phoronix. Retrieved 2013-04-03. 
  10. ^ http://www.linuxplumbersconf.org/2013/ocw/sessions/1107
  11. ^ http://www.linuxplumbersconf.org/2013/ocw/proposals/1551
  12. ^ http://www.linuxplumbersconf.org/2013/ocw/sessions/1467
  13. ^ http://www.linuxplumbersconf.org/2013/ocw/sessions/1317

External links[edit]