The problem with your setup is that you're using TVs for multiple displays.  Like you said, TV's don't understand DPMS so it's impossible to get them to power down on command.  Most newer TVs do understand CEC and it's possible to get a CEC injector (I believe NVIDIA doesn't handle it in their cards) to send a signal for the TV to power itself off/on when you want it to.  The biggest problem is that when TVs turn off, they stop,for the most part, reporting on the cable that they are there, so from the point of view of your system, you are unplugging and plugging in the TV's from the system, probably in some random order, and the system has to quickly deal with handing changing scenarios of one monitor configuration after another as the TVs turn on... It's probably freaks out because it's asked to setup a display on one TV.... no wait 2 TVs...  Just kidding 3 TVs... but it's still trying to handle the first one by the time it's asked to handle the 3rd one.  I have a feeling that TV's also don't have the unique ID's that monitors have so it will also struggle to  automatically place them back in the correct order once they are all up and running if you are using the same model TVs for all your displays.

I personally use a single 50" 4K display for my desktop and other than having to turn it on and off by hand, it has worked flawlessly for the past 5 or 6 years... but then again, I'm only using the one TV for my display.  Before that I used a 3 monitor setup, with actual computer monitors and I didn't have any problems at all with that.  My brother had a system with I believe 16 computer monitors and that worked  very well as well, but again that were actual monitors.

I think I remember coming across a device that was a DPMS proxy that might fix your problem.  It basically sits between you computer and display and fakes a monitor signal to your computer so that your TVs don't appear to be disappearing and reappear to your computer constantly.

You could also hard code your display setup in your Xorg.conf so that it would have no choice but to setup your display like you like it, but that could make things difficult/stange for you at a later date if you ever change your display setup.

Or, you could always get real computer monitors, but that would be very expensive which is probably why your using TVs in the first place.

Brian

On 8/20/20 5:25 PM, Michael Butash via PLUG-discuss wrote:
I have had lots of issues with video and adapters the past few years, mostly as I'm forced to use them.  My nvidia 1070 in my desktop has 3x DP1.2 ports and 1 HDMI2.0.  I have 3 displays, so I use the 3x DP1.2 ports, and run those through adapters to HDMI2.0 on my Samsung TV's I use for monitors.  Non-stop chaos ensues during power-down and up every day, something different, every linux desktop hates it.  Often one display or another will freak out, and I end up; having to hard disconnect the adapter (ie, reboot it) to work again or it'll come up stuck in 768x1024 (on a 48" tv...).

I found HDMI doesn't handle DPMS sort of power-off modes as vga, dvi, dp, or most methods of displays to handle soft power-off scenarios, ala just power down displays.  When my laptop powers them down, they remain on with no signal, which seems to just confuse the video card and adapter that both freak out.  This seems to have a profound effect on displaya and video cards that don't realize most displays are now hdmi...

Graphic subsystems are a basketcase these days under linux, mostly because of these damn adapters, dongles, and vendor wars.  Intel, that wants to sell all the things, including the most useless gpu on the earth, injects themselves into everything, and always cause me issues as I can't convince the os to use the (real) nvidia gpu.  Probably the same sort of issue if an intel gpu is around with AMD.  Last I used an AMD GPU some 4-5 years ago, it was an issue.  Nvidia Prime via Intel is still sketchy af.

Even on a dedicated nvidia gpu in a server-ish xeon system, with DP-to-whatever adapters I had nothing but issues.  My latest iteration is my laptop (xps 9560) and a thunderbolt3/usb-c dock with 2x 4k/60hz outputs via one-piece DP-to-HDMI cables.  I still have quirks, but I've learned to work around, and now somewhat understand really odd hardware behaviour enough to reproduce it.  Occasionally I still need to disconnect a display at the DP-to-HDMI cable I use now, which is again oddly random.

I don't like the adapters, but my 48" TV's I use for displays don't often come with DP ports native, and using HDMI comes with power management oddities.  A lot depends on your cabling and even display these days.

-mb


On Wed, Aug 19, 2020 at 1:05 PM Seabass via PLUG-discuss <plug-discuss@lists.phxlinux.org> wrote:
No, on the desired monitor, it still black screens.

Works just fine (Even without that parameter) on something that has a direct HDMI cable, though. (TV)

> Message: 6
>Date: Tue, 18 Aug 2020 16:23:47 -0700
> From: Aaron Jones <retro64xyz@gmail.com>
> To: plugaz@codezilla.xyz, Main PLUG discussion list
> <plug-discuss@lists.phxlinux.org>
>Subject: Re: KMS but AMDGPU And Black Screen
> Message-ID: <6B7D5942-0F2F-4DAE-A54A-19215718DCF2@gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> https://bugzilla.redhat.com/show_bug.cgi?id=1594488
>
> Set amdgpu.dc=0 in bios and it will work but without hdmi sound.
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