xorg.conf question

[Aaron Plattner]

These are NVIDIA-specific options so they're kinda offtopic here, but 
I'll try to address them below.

You might want to consider posting on the NVIDIA forum 
<https://forums.developer.nvidia.com/c/gpu-unix-graphics/linux/148> [1] 
or by emailing linux-bugs at nvidia.com <mailto:linux-bugs at nvidia.com>

[1] https://forums.developer.nvidia.com/c/gpu-unix-graphics/linux/148

On 3/4/21 9:36 AM, Greene, Paul J. wrote:
>
> Hello,
>
> First post on this list – don’t be too hard on me. J
>
> I support a bunch of software developers that use a KVM to switch back 
> and forth between a Windows workstation and a CentOS 7.9 workstation. 
> The Windows side has dual monitors, both going through the KVM, and 
> the Linux side has 3 monitors – two monitors going through the KVM and 
> the 3^rd monitor connected directly to the PC.
>
> In some cases, when they switch back and forth between the Windows PC 
> and the Linux PC, the Linux PC loses its video resolution or 1 or more 
> screens goes black. I’m assuming the video loses its sync with the 
> monitor. To get out of this state, the user usually does a 
> CTRL-ALT-BACKSPACE to restart X, or they go to CTRL-ALT-F2, login from 
> the command prompt, and type “startx”. In both cases they lose any 
> unsaved work they’ve got open.
>
> The video card (in most cases) is an NVIDIA 620 with the NVIDIA driver 
> installed.
>
> I’ve tried adding the following 4 lines to xorg.conf in the device 
> section, and it seems to make only the left most monitor stable, but 
> the other 2 monitors appear to be disabled, with black screens.
>
> Option         "ConnectedMonitor" "DFP-0"
>
> Option         "CustomEDID" "DFP-0:/etc/X11/edid.bin"
>
> Option         "IgnoreEDID" "false"
>
> Option         "UseEDID" "true"
>
If there's only one GPU in the system then you only need one Device 
section. It's likely that the other two device sections are ignored. 
("Device" here refers to a GPU, not a physical display device).

The "ConnectedMonitor 
<https://download.nvidia.com/XFree86/Linux-x86_64/460.56/README/xconfigoptions.html#ConnectedMonitor>" 
option takes a comma-separated list of display devices that the driver 
should always consider connected. "CustomEDID 
<https://download.nvidia.com/XFree86/Linux-x86_64/460.56/README/xconfigoptions.html#CustomEDID>" 
uses a semicolon-separated list. So in your case you probably want this:

Option "ConnectedMonitor" "DP-0, DP-2, DP-6"
Option "CustomEDID" "DP-0:/path/to/edid0.bin; DP-2:/path/to/edid1.bin; 
DP-6:/path/to/edid2.bin"

These options are documented in the README: 
https://download.nvidia.com/XFree86/Linux-x86_64/460.56/README/xconfigoptions.html

You shouldn't need the IgnoreEDID or UseEDID options.

> The system sees the 3 monitors as DP-2, DP-0, and DP-6 (respectively, 
> from left to right). The NVIDIA driver includes a GUI configuration 
> app that lets you generate the EDID files on each of the monitors, so 
> I created an edid.bin file for each monitor, and adjusted the file 
> path for each one in the 2^nd line.
>
> There’s 3 device sections so I put the 4 lines above into each section 
> (adjusting for edid.bin path and DP-x reference appropriately). That 
> gave me one useable screen (the left one) – the middle and right 
> monitor were black screens.
>
> I tried putting the 4 lines all in one “Device” section, with the 
> appropriate DP-x and edid.bin path, (total of 8 lines) and got the 
> same result.
>
>
Options in xorg.conf don't combine when you have more than one of the 
same option in a section.

-- Aaron

> The PCs are Dell Optiplex 9020s, if that’s relevant.
>
> Any suggestions? Am I on the right track here or should I be trying 
> something else?
>
> PG
>
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