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#1 2023-09-18 01:58:41

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

[SOLVED]Multiple monitor issue on Wayland

Hello,

I recently moved my desktops from a HP Prodesk 600 to a HP t730 thin client (as I want to repurpose my Prodesk as a low power Proxmox server) and now my multiple displays don't work as expected.

The Prodesk has: DP-1, DP-2 and VGA outputs. I had connected 3 monitors to it and used it without any issues.

Since moving to the t730 thin client which has 4 DP outputs (although I have only connected 2 monitors this time around) I have a weird problem. If I poweroff my monitors using the power switch on the monitors, then upon switching the monitors back on again, I get just a gray screen. No mouse, no desktop windows and even the swaylock doesn't display the keypresses from the keyboard. However, if I switch the monitors off again, but only switch ONE of them on again, I am able to get to the desktop and the computer works flawlessly with ONE monitor. However, once it works and if I switch on the 2nd monitor again, I get gray screens on both monitors again and I have to then switch them both off again and only start ONE of them. This is NOT after the computer goes to sleep/hibernate or anything. It happens even after I reboot and immediately switch off the monitors and switch them back on 5 seconds later. Once in a while, if I disconnect the DP cable and reconnect it, both monitors will work, but this is not consistent and most times even disconnect /reconnect of the DP cable doesn't enable the 2nd monitor to work.

I read a few threads related to kernel bug with 2 DP monitors, but I tested that and upon reboot both the monitors work just fine. It's only when I power switch them off and then turn them on again, that the issue occurs. I will also test this out by keeping the monitors powered but waiting for the swaylock to timeout and set the dpms off and see if it behaves differently.

I am using Wayland and so I only have mesa installed and am NOT using the amdgpu drivers. (The Prodesk was an Intel based computer - so I thought it might be a video driver issue, but it doesn't seem like it)

I read some related threads like : https://bbs.archlinux.org/viewtopic.php?id=260159 but that seems to be an issue with X11 and not wayland.

I am unable to understand why this happens. Any pointers?

Last edited by Inxsible (2023-12-24 19:16:49)


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#2 2023-09-18 15:29:27

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

Re: [SOLVED]Multiple monitor issue on Wayland

I tested this by setting a very low value for the timeout for swayidle but the monitor was responsive and took in my password and brought back the desktop. Even manually setting dpms off and then setting it back on (blindly) works as expected. So I don't think this is an issue with the dpms.
Here's my swayidle config just in case:

 exec swayidle -w \
          timeout 900 'swaylock -f -c 000000' \
          timeout 1200 'swaymsg "output * dpms off"' \
               resume 'swaymsg "output * dpms on"' \
          before-sleep 'swaylock -f -c 000000'

Only when I turn the monitor's power switch off, the problem arises. I used the same monitors with the Prodesk and didn't have any issues. For testing, I reconnected the Prodesk to the same monitors and had no issues. It seems that the thin client kills the signal to the DP cables if the monitors are switched off and for whatever reason cannot reset back when the monitors are switched back on.

If I connect only 1 monitor to the HP thin client, I have ZERO issues and everything works as expected, even when power switching the monitor off and then on again.

Any help here please??


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#3 2023-09-19 02:34:49

Skidout
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Registered: 2023-05-26
Posts: 37

Re: [SOLVED]Multiple monitor issue on Wayland

The only thing I can think of is to try using the linux-drm-tip-git kernel and see if that fixes it, but it seems like it might actually be an issue with Sway.

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#4 2023-09-19 14:23:31

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

Re: [SOLVED]Multiple monitor issue on Wayland

Skidout wrote:

The only thing I can think of is to try using the linux-drm-tip-git kernel and see if that fixes it, but it seems like it might actually be an issue with Sway.

It wouldn't work with the Prodesk either in that case. It's probably a combination of a few things in my opinion. amd vs intel, dpms, sway.

Right now I have resorted to just using a single monitor, even though I have 3 sitting on my workdesk.


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#5 2023-09-19 14:37:17

Lone_Wolf
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From: Netherlands, Europe
Registered: 2005-10-04
Posts: 12,181

Re: [SOLVED]Multiple monitor issue on Wayland

Do your monitors support DisplayPort Multi Stream Transport aka MST aka daisy-chaining  ?

If so, make sure it is set to disabled on every monitor except ones that are using it.


Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.


(A works at time B)  && (time C > time B ) ≠  (A works at time C)

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#6 2023-09-27 01:05:55

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

Re: [SOLVED]Multiple monitor issue on Wayland

Lone_Wolf wrote:

Do your monitors support DisplayPort Multi Stream Transport aka MST aka daisy-chaining  ?

If so, make sure it is set to disabled on every monitor except ones that are using it.

No, I don't think they support daisy-chaining. In any case, I was connecting the monitors directly to the hp t730 DP ports.


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#7 2023-12-22 23:46:38

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

Re: [SOLVED]Multiple monitor issue on Wayland

Upping this again.

I found that computer seems to be responding when I turn on both the monitors but the screens remain gray. I just ran

swaymsg -t get_outputs

command unseen and then turned both monitors off, and then turned on only 1. The command had displayed the result for both the monitors indicating that the computer seems to be recognizing both monitors but for some reason the screen display doesn't work.

What else can I look into? I am basically switching off the monitors to save power when I am not around the desktop. Would letting dpms do it's job be the same thing in terms of power consumption?

Last edited by Inxsible (2023-12-22 23:48:13)


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#8 2023-12-24 15:34:01

seth
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Registered: 2012-09-03
Posts: 53,421

Re: [SOLVED]Multiple monitor issue on Wayland

Would letting dpms do it's job be the same thing in terms of power consumption?

Most of it, obviously the monitor is still "active" (it can respond to events and you maybe also have a bezel light?) but in an ideal world the power consumption is drastically reduced during dpms standby/off and almost™ as good as a hardware power switch.
1. "almost"
2. "ideal world" - the monitors tech sheet will likely indicate this and there some EU reg… ok, Chicago isn't exactly in the EU.
But to really know, you'll have to measure the consumption anyway.

The poweroff switch will unregister the monitor and then the handshake fails when you toggle it on again - does it show up if you
- switch to a different VT?
- change the display resolution?

Is it always the same monitor or the same DP output that fails or is this totally random?
(What happens if you switch the outputs ie. plug M1 into DP2 and vv?)

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#9 2023-12-24 18:35:35

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

Re: [SOLVED]Multiple monitor issue on Wayland

seth wrote:

Would letting dpms do it's job be the same thing in terms of power consumption?

Most of it, obviously the monitor is still "active" (it can respond to events and you maybe also have a bezel light?) but in an ideal world the power consumption is drastically reduced during dpms standby/off and almost™ as good as a hardware power switch.
1. "almost"
2. "ideal world" - the monitors tech sheet will likely indicate this and there some EU reg… ok, Chicago isn't exactly in the EU.
But to really know, you'll have to measure the consumption anyway.

Thanks for giving me something to test. Yes the monitor's power switch has a small LED light indicating power, although, the monitor also has a setting to keep that LED off even when powered on.

seth wrote:

The poweroff switch will unregister the monitor and then the handshake fails when you toggle it on again - does it show up if you
- switch to a different VT?

No the monitors don't show anything on screen. I do notice that the backlight goes off and then on again indicating that it switched the VT but nothing can be seen on screen except the backlight. Switching off all monitors and then switching on only 1 confirms this because I am on a different VT at that point.

seth wrote:

- change the display resolution?

Same result

seth wrote:

Is it always the same monitor or the same DP output that fails or is this totally random?

No, I have 3 similar monitors and I have tried different combinations (the t730 has 4 DP. I have tried all combinations and permutations. When rebooting the computer, the monitors work fine It even works with 3 displays. But once the dpms kicks in -- or if I power switch the monitors off, then the multiple screens never come back on again unless I reboot.

seth wrote:

(What happens if you switch the outputs ie. plug M1 into DP2 and vv?)

No change. Once the monitors go blank, even if I change the DP ports behind the unit, it still makes no difference as long as more than 1 monitor is "on". If I power switch off ALL but one, then that single monitor displays and works just fine.

As per the HP t730 specs, the built in AMD Radeon HD 9000 is capable of driving 4 monitors:  https://h20195.www2.hp.com/v2/getpdf.aspx/c04743502.pdf  (Page 4)

Native support for up to four (4) displays @ Ultra HD/4K (3840 x 2160) resolution. System provides four (4) DisplayPort 1.2
digital video output ports at the back of the unit
The HP t730 Thin Client supports a 60 Hz screen refresh rate for up to two Ultra HD displays set for UHD/4K resolution; when
three or four Ultra HD displays set for UHD/4K resolution are connected the maximum screen refresh rate supported for all
displays is 30 Hz. All displays set for resolutions lower than UHD/4K support a maximum screen refresh rate of 60 Hz.

Moreover, all my monitors are just 1080P, so it should be able to drive all 4 at 60Hz as far as I understand.

Last edited by Inxsible (2023-12-24 18:43:33)


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#10 2023-12-24 19:02:36

Inxsible
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Re: [SOLVED]Multiple monitor issue on Wayland

Tested some more and I think it's related to the dpms.
I changed my swayidle setting to

 exec swayidle -w \
          timeout 9 'swaylock -f -c 000000' \
          timeout 900 'swaymsg "output * dpms off"' \
               resume 'swaymsg "output * dpms on"' \
          before-sleep 'swaylock -f -c 000000'

So basically I am locking the screen in 6 seconds, but not turning off dpms immediately. In this case, once the swayidle kicked in after 6 seconds, I was still able to utilize all 3 screens, Swaylock would display on all 3 screens and once logged in, I am able to use all 3 screen as well.

I think it's the "swaymsg output * dpms off" command is causing the issue. However, this used to work flawlessly when I was using a different hardware unit (prodesk 600). I will try and change the dpms for the individual monitors and see if that affects anything.


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#11 2023-12-24 19:14:43

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

Re: [SOLVED]Multiple monitor issue on Wayland

That was it.
I changed the final swayidle config to :

 exec swayidle -w \
          timeout 6 'swaylock -f -c 000000' \
          timeout 9 'swaymsg "output DP-1 dpms off"' \
          timeout 9 'swaymsg "output DP-2 dpms off"' \
          timeout 9 'swaymsg "output DP-3 dpms off"' \
               resume 'swaymsg "output * dpms on"' \
          before-sleep 'swaylock -f -c 000000'

This then allows me to utilize all the monitors correctly. Turning of dpms on * was somehow causing an issue where the resume * wasn't able to restart it correctly. With explicitly turning off dpms on each individual monitor, the resume * works fine. But again I think this is probably hardware dependent too since the * used to work fine with my other archlinux desktops.

I'll change the timeouts back to some decent values -- say 600 for swaylock & 900 for dpms

Thanks.

Last edited by Inxsible (2023-12-24 19:15:40)


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#12 2023-12-25 22:43:54

Inxsible
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From: Chicago
Registered: 2008-06-09
Posts: 9,183

Re: [SOLVED]Multiple monitor issue on Wayland

Seems like I spoke too soon. Turning off dpms definitely doesn't jive well with this particular box. So I have resorted to simply locking the screen and changed my swayidle command to

exec swayidle -w \
         timeout 600 'swaylock -f -c 000000'\
         before-sleep 'swaylock -f -c 000000'

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