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KDE Plasma - Can't Configure Multiple X Screens on One Card
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jasn
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Joined: 05 May 2005
Posts: 439
Location: Maryland, US

PostPosted: Tue Jul 11, 2017 4:51 am    Post subject: KDE Plasma - Can't Configure Multiple X Screens on One Card Reply with quote

Using the nvidia-drivers-384.47 and the instructions here, I can't configure my system to have two separate X servers using one nVidia card and my two displays, (laptop screen and desktop monitor). Both monitors will work as an extended display, but I can't get them to work separately. I used the nvidia-settings program to define the xorg.conf settings, and it provides me with the following;
Code:
# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings:  version 384.47

Section "ServerLayout"
    Identifier     "Layout0"
    Screen      0  "Screen0" 0 0
    Screen      1  "Screen1" RightOf "Screen0"
    InputDevice    "Keyboard0" "CoreKeyboard"
    InputDevice    "Mouse0" "CorePointer"
    Option         "Xinerama" "0"
EndSection

Section "Files"
        ModulePath "/usr/lib64/opengl/nvidia"
        ModulePath "/usr/lib64/xorg/modules"
EndSection

Section "InputDevice"
    # generated from data in "/etc/conf.d/gpm"
    Identifier     "Mouse0"
    Driver         "mouse"
    Option         "Protocol"
    Option         "Device" "/dev/input/mice"
    Option         "Emulate3Buttons" "no"
    Option         "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"
    # generated from default
    Identifier     "Keyboard0"
    Driver         "kbd"
EndSection

Section "Monitor"
    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor0"
    VendorName     "Unknown"
    ModelName      "AUS ROG PG278QR"
    HorizSync       34.0 - 240.0
    VertRefresh     30.0 - 165.0
    Option         "DPMS"
EndSection

Section "Monitor"
    # HorizSync source: edid, VertRefresh source: edid
    Identifier     "Monitor1"
    VendorName     "Unknown"
    ModelName      "AU Optronics Corporation"
    HorizSync       137.2 - 137.2
    VertRefresh     60.1 - 120.1
    Option         "DPMS"
EndSection

Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 1070"
    BusID          "PCI:1:0:0"
    Screen          0
EndSection

Section "Device"
    Identifier     "Device1"
    Driver         "nvidia"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 1070"
    BusID          "PCI:1:0:0"
    Screen          1
EndSection

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "nvidiaXineramaInfoOrder" "DFP-4"
    Option         "metamodes" "DP-3: nvidia-auto-select +0+0"
    Option         "SLI" "Off"
    Option         "MultiGPU" "Off"
    Option         "BaseMosaic" "off"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Section "Screen"
    Identifier     "Screen1"
    Device         "Device1"
    Monitor        "Monitor1"
    DefaultDepth    24
    Option         "Stereo" "0"
    Option         "metamodes" "DP-0: nvidia-auto-select +0+0"
    Option         "SLI" "Off"
    Option         "MultiGPU" "Off"
    Option         "BaseMosaic" "off"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Using this configuration, my plasma desktop will start on my main monitor, but my laptop screen will remain blank. I can move my mouse cursor from one screen to the other, but there's no desktop present on my laptop screen. Additionally, the KDE System Settings -> Display and Monitor -> Displays will only show my main desktop monitor. If I comment out the entire ServerLayout section I can get both displays to work, but only in extended mode.

Lastly I notice some posts of folks not using any /etc/X11/xorg.conf.d files, but if I don't at least have the File section configuration;
Code:
Section "Files"
        ModulePath "/usr/lib64/opengl/nvidia"
        ModulePath "/usr/lib64/xorg/modules"
EndSection

I won't get an X server at all. My system will boot directly to a login prompt. If I include only that configuration file, my desktop will boot up correctly, and I can use an extended display across both monitors, but it sets up the scaling DPI based on my laptop screen, which is too big for my desktop monitor. Is there any way yet to have all monitor settings auto detected correctly? I'm thinking that it might be nice when I have to switch between my desktop configuration and laptop.

Thanks..
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asturm
Developer
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Joined: 05 Apr 2007
Posts: 6822
Location: Austria

PostPosted: Tue Jul 11, 2017 4:54 pm    Post subject: Re: KDE Plasma - Can't Configure Multiple X Screens on One C Reply with quote

jasn wrote:
Using the nvidia-drivers-384.47 and the instructions here, I can't configure my system to have two separate X servers using one nVidia card and my two displays

I don't think this (zaphod mode?) is supported by modern DEs at all. But I'm no expert wrt multiscreen.

I personally haven't configured xorg.conf in years, but this is all you should need (forget any automatic settings generator):

Code:
Section "Device"
    Identifier     "MyDevice"
    Driver         "nvidia"
EndSection

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backend.cpp:92:2: warning: #warning TODO - this error message is about as useful as a cooling unit in the arctic
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jasn
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Joined: 05 May 2005
Posts: 439
Location: Maryland, US

PostPosted: Wed Jul 12, 2017 1:07 am    Post subject: Re: KDE Plasma - Can't Configure Multiple X Screens on One C Reply with quote

asturm wrote:
I don't think this (zaphod mode?) is supported by modern DEs at all. But I'm no expert wrt multiscreen.

You may be right. (BTW, I never knew the nickname. Had a great chuckle looking it up and then remembering Sam Rockwell in the movie.) I've seen some posts online suggesting that this may be a feature enabled with Wayland, but nothing concrete. The interesting thing is if I use the xorg.conf as configured, when my desktop launches, I get dual KDE loading screens, one the size of my desktop monitor, the other the size of my laptop monitor, overlaid onto each other, on my desktop monitor. It's like it's trying to do it, it just can't figure out to put the one X server desktop on my laptop screen. Oh well. I may try out wayland to see if anything is different there.

asturm wrote:
I personally haven't configured xorg.conf in years, but this is all you should need (forget any automatic settings generator):

Code:
Section "Device"
    Identifier     "MyDevice"
    Driver         "nvidia"
EndSection

I'd love to be able to do so as well. However, if I don't at least include the Files section above, I get a black desktop and my Xorg.0.log says that the system failed to load the GLX module. In fact I can bring up my desktop with just the Files section above, however it's with the wrong DPI. I think it's using the same DPI for both screens, and it's too big for my desktop monitor. I basically have to include the Monitor, Device, and Screen sections to get it to use the right DPI.

Thanks..

BTW. This isn't a show stopper. The extended desktop works just fine. I'm setting up some game streaming and wanted to use my laptop as my session monitor and it works using the extended monitor mode, I just have to make sure I have the right screens in the right virtual desktop when I load my game. I just figured having an independent X server instance, would give me more control.
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jasn
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Joined: 05 May 2005
Posts: 439
Location: Maryland, US

PostPosted: Thu Jul 13, 2017 2:53 am    Post subject: Reply with quote

So while not finding a way to enable configuring separate X Screens on two displays using one nVidia GPU, I was able to simplify my xorg configuration for enabling extending a single display across both screens, and get the DPI I want. I now only have 2 configuration files in /etc/X11/xorg.conf.d/
Code:
20opengl.conf
Section "Files"
        ModulePath "/usr/lib64/opengl/nvidia"
        ModulePath "/usr/lib64/xorg/modules"
EndSection

Code:
50device.conf
Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
        Option      "UseEdidDpi" "False"
        Option      "DPI" "96 x 96"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 1070"
EndSection
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BobWya
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Joined: 12 Aug 2012
Posts: 227
Location: Cambridge,UK

PostPosted: Mon Jul 24, 2017 9:37 pm    Post subject: Reply with quote

jasn wrote:
So while not finding a way to enable configuring separate X Screens on two displays using one nVidia GPU, I was able to simplify my xorg configuration for enabling extending a single display across both screens, and get the DPI I want. I now only have 2 configuration files in /etc/X11/xorg.conf.d/
...
Code:
50device.conf
Section "Device"
    Identifier     "Device0"
    Driver         "nvidia"
        Option      "UseEdidDpi" "False"
        Option      "DPI" "96 x 96"
    VendorName     "NVIDIA Corporation"
    BoardName      "GeForce GTX 1070"
EndSection


Thanks - I've borrowed that "DPI hack" for my dual monitor setup...

Btw to my knowledge the only "major Linux desktop" still supporting multihead X is Xfce.
The last KDE Desktop to support this was the 3.x series. Despite lots of moaning about this missing from KDE 4!!
The bug reports are still up on the KDE website - if you want a depressing read... E.g. Bug 256242 - Please support Multi-Screen-Setup (seperate X-Servers) in kwin ...

Bob
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