Re: Restarting video driver to turn on external vga port

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On Fri, 2023-06-30 at 13:26 -0400, Robert Moskowitz wrote:
> And what is EDID?  And would that come through the KVM?

It's the monitor identifying itself to the video card.  With very old
VGA monitors that could have been just one or two spare pins in the
plug grounded, indicating a certain video mode to be used (and that
sort of thing might only be noticed by a few graphics cards).  With
much more modern hardware, it's serial data transmitted from the
monitor.  The monitor literally identifies itself, and lists its
supported video modes.  Your graphics system would then look through
the table of supported modes for the monitor (scan rates and dot
clocks), likewise for the graphics card, and automatically select the
best mode that both can do.

Some KVMs can tell all their remote PCs what the attached monitor tells
it about itself.  Other's will simply provide some dummy info to get
the PC to give it a video signal.  Then you just have to hope things
work.  If you had a KVM which specifies that it only supports one or
two graphics modes, I'd suspect it's one of those that ignores your
monitors EDID.

Other users who've had problems with their monitors providing incorrect
information to their graphics card have found ways to shoehorn in their
own custom data to override it.  Going from memory, I think Tom Horsley
on this list was one of them.

The same thing (faking your own custom EDID) could help with monitors
with failing EDID circuitry, or broken VGA cable wiring.

-- 
 
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