[Server-devel] [XSCE] CentOS 7 quirk: VGA cable not re-attachable

[James Cameron]

On Mon, Aug 29, 2016 at 10:13:44PM -0400, Adam Holt wrote:
> - Fun Curiosity: you can reliably pull the power cable out of the
> LCD screen (or power cycle the LCD monitor with its own ON/OFF
> button) and VGA video *will* quite survive amazingly, promptly
> re-appearing on screen, anytime later when the monitor's power (or
> power cord) restores electricity!

That's normal, not curious.

Please learn this; your monitor has a device that is powered over the
cable by the computer, even if the power cable is out.  The device
says "here I am and this is what I can do!".

Key words for further educational searches; Display Data Channel
(DDC), Extended Display Identification Data (EDID).

My guess is that the driver for the DisplayPort or VGA adapter needs
an update, and an examination of the kernel events may show
differences between CentOS 7.2 and Fedora 22 at the instant of
plugging.  Give it to someone technical; someone who has good
understanding of the whole stack of components.  Maybe you can get the
fix backported to CentOS 7.2.

VGA connectors are not hotpluggable.  You'll notice the pins are all
the same length.  While it often works, there's no guarantee.

Oh, look, Wikipedia says that.

"Hot pluggable: Depends"

"The VGA interface is not engineered to be hotpluggable (so that the
user can connect or disconnect the output device while the host is
running), although in practice this can be done and usually does not
cause damage to the hardware or other problems. However, nothing in
the design ensures that the ground pins form the first makek or the
last break in the connection, so hotplugging may introduce surges in
signal lines which may or may not be adequately protected against
damage. Also, depending on the hardware and software, monitor
detection is sometimes unreliable when hotplugging a VGA connection."

... complete with obligatory typo.  ;-)

-- 
James Cameron
http://quozl.netrek.org/