Re: Monitors not coming out of power save when turned off
On Fri, 29 Oct 2021 11:39:40 +0100
Mike <debian@norgie.net> wrote:
> Folks,
>
> I have a desktop running Debian 11 with two monitors connected via
> Display Port to my Nvidia graphics card. I have something of an issue
> with power save. I haven't configured any power saving, although it
> uses the standard X settings, which I believe is standby/poweroff/etc
> all set to 300 seconds. This works find and after five mins or
> whatever it is the monitors go into power save, though generally, if
> I'm moving away from the computer for a while I'll hit the power
> switch.
>
> The issue comes when I return. If I turn the monitors back on and
> then move the mouse, everything powers back on. If I happen to move
> the mouse before powering on the monitors, they do not come out of
> power save. I beleive this is to do with X being able to detect the
> presence of the monitor and if it seen no monitors (because they are
> powered off), then it disables them. I haven't found a way out of
> this mess, other than to SSH into the host and reboot. It's
> interesting that X doesn't appear to care abou the monitors going
> off/on. Turning one off doesn't cause the display to shift to the
> remaining monitor. It only appears to happen after X has gone into
> powersave. It's also worth adding this is all hyphthosis, I haven't
> fully confirmed it to be the cause.
>
> I have read of similar things happening and people getting around it
> by masking the power detect pin on the display cable, although this
> seems a little bit of a messy fix. Especially given it's reportedly
> a lot more fiddly to do on a Display Port cable.
>
> Anyway, can anyone offer any advice on this situation? It it possible
> to configure X to ignore the monitor power state? Is there any way to
> recover the situation without having to blindly reboot? Have I
> totally missed something and the cause of this mishap actually
> something I haven't considered?
>
> Any assistance would be appreciated.
>
>
It's probably an HDMI thing, which is pretty much the same as Display
Port. One end typically will not turn on unless it sees something
hanging on the other end. Sometimes terminating resistors appear to be
enough, sometimes it wants to see something active. Some HDMI
connections and cables pass a 5V line, some older ones don't.
My worst case of it was a laptop and a Grundig-branded monitor. There
was no way I could get them to work together, though each would work
with other HDMI equipment. I tried timing the power on to both over a
wide range, in case one would stay in detection mode longer than the
other, but I never managed to get them to connect.
--
Joe
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