Architecture

DRM

https://en.wikipedia.org/wiki/Direct_Rendering_Manager#Hardware_support

radeon: until GCN 2nd gen
amdgpu: since GCN 3rd gen, 1st gen experimental

nouveau NVIDIA Tesla, Fermi, Kepler, Maxwell based GeForce GPUs, Tegra K1, X1 SoC
tegra Nvidia Tegra20, Tegra30 SoCs

bochs Virtual VGA cards using the Bochs dispi vga interface (such as QEMU stdvga)

https://keyj.emphy.de/files/linuxgraphics_en.pdf (page 35)

https://www.kernel.org/doc/Documentation/fb/framebuffer.txt
The frame buffer device provides an abstraction for the graphics hardware.

http://betteros.org/tut/graphics1.php
Supposedly, fbdev is the "old" way of doing things, and KMS/DRM is the "new" way.

https://elinux.org/images/7/71/Elce11_dae.pdf
Control all HW thru a single device node

https://events.linuxfoundation.org/sites/events/files/slides/brezillon-drm-kms.pdf
https://01.org/linuxgraphics/gfx-docs/drm/gpu/introduction.html

dmesg | grep modesetting
cat /sys/class/drm/card0/device/{label,uevent}

GEM (Graphics Execution Manager): Framework for buffer management.

Driver source

https://cgit.freedesktop.org/xorg/driver/
https://cgit.freedesktop.org/xorg/driver/xf86-video-ati/log/

Kernel Mode Setting (KMS)

https://wiki.archlinux.org/index.php/kernel_mode_setting
Previously, setting up the video card was the job of the X server.
kernel is now able to set the mode of the video card. This makes fancy graphics during bootup, virtual console and X fast switching possible, among other things.

Installation

Any vga= options in your bootloader as these will conflict with the native resolution enabled by KMS.
Any video= lines that enable a framebuffer that conflicts with the driver.
Any other framebuffer drivers (such as uvesafb)

Intel, Nouveau, ATI and AMDGPU drivers already enable KMS automatically.
The proprietary NVIDIA driver supports KMS (since 364.12), which has to be manually enabled.
The proprietary AMD Catalyst driver does not support KMS

Direct Rendering Infrastructure (DRI)

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.[citation needed]

XFree86

version 4.8.0 released on 15 December 2008

Wayland



a prospective replacement for X.
It works directly with the GPU hardware, via DRI. Wayland can run an X.org server as a client, which can be rootless
based on EGL and DRI

Ubuntu 17.10 (Artful Aardvark) ships Wayland as default
Fedora 25+ uses Wayland for the default GNOME 3.22 desktop session
RebeccaBlackOS: https://sourceforge.net/projects/rebeccablackos/files/

X Window System (X11 or X)

https://en.wikipedia.org/wiki/X_Window_System
The protocol[clarification needed] has been version 11 (hence "X11") since September 1987.

the client and server may run on the same machine or on different ones

An X client itself may emulate an X server by providing display services to other clients. This is known as "X nesting". Open-source clients such as Xnest and Xephyr support such X nesting.

Releases

No release plan for a X11R7.8 rollup katamari release has been proposed.
Unlike X11R1 through X11R6.9, X11R7.x releases are not built from one monolithic source tree, but many individual modules.

X11R7.6

allow fragments of the X server configuration to be delivered in individual files
running the server without a configuration file

X11R7.7

https://www.x.org/releases/X11R7.7/doc/xorg-docs/ReleaseNotes.html
an Open Source version of the X Window System that supports Linux, BSD, Solaris, Cygwin and MacOS X on Intel and other platforms.

Some multi-head configurations are supported in X11R7.7. Support for multiple PCI/AGP cards may require a kernel with changes to support VGA arbitration.

All users must now set DPI or some other scaling factor explicitly

Config

https://www.x.org/releases/X11R7.7/doc/index.html
https://www.x.org/releases/X11R7.7/doc/man/man5/xorg.conf.5.xhtml
https://www.x.org/releases/X11R7.7/doc/man/man4/radeon.4.xhtml

Commands: https://www.x.org/releases/X11R7.7/doc/man/man1/ Drivers: https://www.x.org/releases/X11R7.7/doc/man/man4/

X.Org Server

https://www.x.org/releases/individual/xserver/
implementation of the display server for the X Window System

The Xorg server relies on the operating system's native module loader support for handling program modules. The X server makes use of modules for video drivers, X server extensions, input device drivers, framebuffer layers, and internal components used by some drivers (like XAA & EXA).

# Xorg -version
    X.Org X Server 1.19.5
    X Protocol Version 11, Revision 0

https://keyj.emphy.de/files/linuxgraphics_en.pdf
X Server manages input (keyboard, mouse, ...) and output (graphics only)

The X Protocol can be extended with new functionality via Extensions. Examples:
◾ XSHM (»X Shared Memory«) – faster local display of bitmap graphics
◾ Xv (»X Video«) – hardware-accelerated video display
◾ GLX – OpenGL on X
◾ Xinerama – multi-monitor support
◾ XRandR (»X Resize and Rotate«) – graphics mode setting without restarting the X
Server
◾ XRender – modern anti-aliased, alpha-blended 2D graphics
    ▸ today used for (almost) every 2D graphics application

RandR ("resize and rotate")

xrandr
    Screen 0: minimum 0 x 0, current 1234 x 823, maximum 4096 x 4096

xrandr --output VGA1 --off  # Disabling an output

Additional specialized X server binaries

Xdmx
is a proxy X server that uses one or more other X servers as its display devices. It provides multi-head X functionality for displays that might be located on different machines.

Xnest
is a nested X server, that operates as both an X client and X server.

Xephyr
is a X server that outputs to a window on a pre-existing “host” X display. Unlike Xnest which is an X proxy, and thus limited to the capabilities of the host X server, Xephyr is a full X server which uses the host X server window as a “framebuffer” via fast SHM XImages.

Xvfb
is a virtual framebuffer X server that can run on machines with no display hardware and no physical input devices. It emulates a dumb framebuffer using virtual memory.

Xquartz
is an X server that interacts with the MacOS X native Aqua window system

Xwin
is an X server that runs under the Cygwin environment: https://x.cygwin.com

OpenGL

https://keyj.emphy.de/files/linuxgraphics_en.pdf

OpenGL driver runs in userspace as part of the application process

additional API required as »glue« to the windowing system:
▸ GLX for the X Window System
▸ WGL (Windows), AGL (Mac OS X)
▸ EGL for OpenGL ES (Embedded Linux, Android, iOS, ...)
    ◦ available on all systems, will eventually supersede GLX etc.

Mesa is an open source OpenGL implementation

X Clients

https://keyj.emphy.de/files/linuxgraphics_en.pdf

X Clients don’t implement the X11 protocol directly, but use libraries:
▸ traditionally Xlib
▸ newer, leaner alternative: XCB (»X11 C Bindings«)
▸ toolkits (Motif, Gtk, Qt, ...) internally use Xlib or XCB, too

Window Manager

special X Client that manages the positions of the top-level windows and draws window frames (»decorations«)

Xsecurity

https://www.x.org/releases/current/doc/man/man7/Xsecurity.7.xhtml

  • Host access: managed using xhost command.a single connection simultaneously.
  • MIT-magic-cookie-1: without encryption.
  • XDM-authorization-1: with encryption.
  • sun-des-1: SunOS (and some other systems)
  • server interpreted: manipulated via xhost

    MIT-MAGIC-COOKIE-1 and XDM-AUTHORIZATION-1 store secret data in the file; so anyone who can read the file can gain access to the X server.
    SUN-DES-1 stores only the identity of the principal who started the server (unix.hostname@domain when the server is started by xdm), and so it is not useful to anyone not authorized to connect to the server.

xhost

/etc/Xn.host

family:name
inet    Internet host (IPv4).
inet6    Internet host (IPv6).
dnet    DECnet host.
nis        Secure RPC network name.
krb        Kerberos V5 principal.
local    Contains only one name, the empty string.
si        Server Interpreted: IPv6/hostname/localuser & localgroup

xhost +         # allow everyone
xhost +SI:localuser:lightdm / si:hostname:almas

xauth

-f authfile
    By default, XAUTHORITY environment variable or ~/.Xauthority.
-q
    quietly.
-v
    verbosely
-i
    ignore any authority file locks
-b
    attempt to break any authority file locks before proceeding
-n
    not attempt to resolve any hostnames

xauth info
xauth list

echo $DISPLAY

[host]:display#.screen#

mons - manage three monitors on X

git clone --recursive https://github.com/Ventto/mons.git
cd mons
sudo make install

Forwarding

https://wiki.archlinux.org/index.php/Secure_Shell#X11_forwarding

AllowTcpForwarding yes
X11Forwarding yes
X11DisplayOffset 10
X11UseLocalhost yes

export XAUTHORITY=~fzinfz/.Xauthority
xauth add $(xauth -f ~fzinfz/.Xauthority list|tail -1)

Debug

https://stackoverflow.com/questions/28392949

ss -anp | grep 6010     # 127.0.0.1:6010 (= 6000+10 for localhost:10.0)
tcpdump -nS -i any port 6010

xpra

re-attachable: http://xpra.org/

apt install -y xpra         # remote
xpra start :13              # remote
xpra attach ssh:remote:13   # local
DISPLAY=:13 xeyes           # remote

vnc

vncserver -kill :1

VGA Switcheroo

https://01.org/linuxgraphics/gfx-docs/drm/gpu/vga-switcheroo.html

Linux subsystem for laptop hybrid graphics. 2 flavors:

  • muxed: both GPUs can drive all displays
  • muxless: only one connected to outputs. The other one is merely used to offload rendering, its results are copied over PCIe into the framebuffer. On Linux this is supported with DRI PRIME.

PRIME

https://wiki.archlinux.org/index.php/PRIME

PRIME is a technology used to manage hybrid graphics found on recent laptops (Optimus for NVIDIA, AMD Dynamic Switchable Graphics for Radeon). PRIME GPU offloading and Reverse PRIME is an attempt to support muxless hybrid graphics in the Linux kernel.

xrandr --listproviders  # check support
xrandr --setprovideroffloadsink 1 0
xrandr --setprovideroffloadsink radeon Intel
DRI_PRIME=1 glxinfo | grep "OpenGL renderer"

# Discrete card as primary GPU, XRandR 1.4+
xrandr --setprovideroutputsource Intel nouveau

    dedicated GPU’s output is copied over to the integrated GPU
    ◦ not saving power (quite the contrary – both GPUs are active!)

https://devtalk.nvidia.com/default/topic/957814/prime-and-prime-synchronization/
https://negativo17.org/complex-setup-with-nvidia-optimus-nouveau-prime-on-fedora-20/

GPGPU (General-purpose computing on GPU)

https://wiki.archlinux.org/index.php/GPGPU

radeontop

make amdgpu=1   # show VRAM usage. requires libdrm >= 2.4.63

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