This is a separate question related to a problem I'm facing with my monitor when using DisplayPort cable. For those interested in the full discussion on that you can find it here:

https://www.bleepingcomputer.com/for...ng-displayport

The gist of the situation and my question now: My monitor won't work properly when connected to a DisplayPort cable. HDMI works without any issue but has a major limitation that's been forcing me back to DP: It only runs at 120 Hz instead of the 144 Hz supported by the monitor. When I looked at this I remember reading it's a hardware limitation, due to my model using an older HDMI version which doesn't allow the bandwidth needed to do 144 Hz @ 1080p resolution. My monitor is a Viewsonic VX2458-C-MHD, here's its official page and the product page of the store I ordered it from:

https://www.viewsonic.com/us/vx2458-...m-monitor.html

https://www.emag.ro/monitor-gaming-l...d/pd/DG678QBBM

I'm now questioning this statement after someone who has the same monitor told me you can in fact do 144 Hz on HDMI not just DP. I was told the 120 Hz cap would be a mere limitation in the AMD driver instead. This would help me greatly as I no longer need to keep trying to use DisplayPort and risk damaging my hardware if that's the case.

But how do I lift this limit? Specifically how do I do it on Linux? I haven't used Windows for a decade and don't plan on touching it again, my OS is Manjaro. The KDE display settings offer me 144 Hz on the problematic DisplayPort but only 120 Hz on HDMI. Is there a command I can use on either the X11 or Wayland session to force the system to let me try the full refresh rate and see if it works? I know xrandr lets you do weird things on X but no idea if I can use it to force the full resolution. Could someone please post the steps required to try this? Thank you.

An update: I tried fixing it with xrandr following an Arch guide but sadly no success.

https://wiki.archlinux.org/title/Xra...ed_resolutions

cvt 1920 1080 144
xrandr --newmode "1920x1080_144.00" 452.50 1920 2088 2296 2672 1080 1083 1088 1177 -hsync +vsync
xrandr --addmode HDMI-A-0 1920x1080_144.00
xrandr --output HDMI-A-0 --mode 1920x1080_144.00

Following the final command the monitor fell in an endless loop of going to sleep, waking up, saying there's no signal, going to sleep again. The 144 Hz option appeared in the system settings as well but had the same result. What do you think is causing that?

https://www.viewsonicglobal.com/publ...mhd_UG_ENG.pdf

As this guide shows my monitor is in fact meant to support 144 Hz even on HDMI. My HDMI cable is 2.0 compatible so it shouldn't be a version limitation either.

Solution found and it is working! Cheers to MichaelDeets on Reddit for his help. The issue with the xrandr command is that cvt and gtf produce excessive clocks by default. In their place I used this calculator and came up with a safe minimum that actually works:

The messy workaround should be simple: Just add this and the other xrandr commands to ~/.profile and the whole thing will be automatically applied on login. But why is this even needed, why can't the system automatically detect the proper settings for 144 Hz as it does for 120 Hz and below... is this a bug worth reporting with the Linux kernel or AMD developers?

Another important question: Eventually there may come that faithful day when KDE users can use the Plasma Wayland session bug free. What's the equivalent to xrandr for Wayland? What commands do I use in its case to set and use a custom mode in the same way?

Do you believe manual mode calculators should be able to better calculate than X itself. With many wacko displays over more than 30 years I've never needed to resort to manual modeline calculation. I give X the data it needs, then let it perform its own automagic calculating. That data, which goes in /etc/X11/xorg.conf.d/*.conf or /etc/X11/xorg.conf, is:

1. HorizSync
2. VertRefresh
3. PreferredMode

Did you ever try the method? I haven't had the opportunity for your situation, as I've never had access to any display supporting 144Hz, nor a GPU supporting more than 60Hz connected to any display supporting more than 60Hz. My eyes aren't good enough to pursue more than 2k.

Can you better explain how the rule in xorg.conf.d is supposed to look please? I'd appreciate the full file as parameters there are often times fiddly. This definitely sounds better if possible!

It should be pretty simple. Make sure display configuration settings anywhere else are purged, particularly those your DE may save in your homedir anywhere, then create /etc/X11/xorg.conf.d/50-monitor.conf containing:man xorg.conf

Do you have the latest motherboard BIOS installed? Is there a firmware upgrade available for the Viewsonic? Have you complained to Viewsonic?

Have you tried using the modesetting DIX display driver instead of amdgpu DDX display driver?

If Taoki is you on that bleepingcomputer page, this smells like an interplay issue between display and PC and/or GPU BIOS. Some motherboard BIOS just don't play nice with some display firmware. I have one NEC display with DVI, HDMI, DP & VGA inputs that simply doesn't like to light up reliably at POST with some motherboards' IGPs using the DP output connection, some using the HDMI, and some using either DP or HDMI, but never a problem with DVI or VGA. I have an Acer that sometimes works fine the first time I log into X, then on logout return to DM greeter it claims unsupported mode, with only some OS/GPU combinations. Getting X output back sometimes requires a reboot, even after Ctrl-Alt-Fn produces a perfectly working vtty. IOW, modern displays just don't get enough testing before being unleashed for sale to the public. If yours is under warranty, I'd get seriously interactive with Viewsonic, and whoever manufactured your AMD GPU card.

Thanks, I shall give that a try! Could be: Mine doesn't play nice with DisplayPort and only HDMI is stable, but HDMI comes with this pesky 120 Hz limit by default.

I'm waiting for the next BIOS to come out of beta already, just upgraded it two weeks ago when they decided to launch a new wave for older boards. I looked and those monitors can't be firmware upgraded, no USB connection and it would probably require Windows too which I no longer have or want to touch. Someone taught me how to use the modesetting driver and override the AMD one, I gave that a try and could confirm it works but it still doesn't make 144 Hz on HDMI show up OOTB.

With amdgpu DDX, using xrandr --output HDMI-A-0 --mode 1920x1080 --rate 144 or just xrandr --output HDMI-A-0 --rate 144 gets ignored, or turns the screen black?

I tried that as well yesterday. Unless I use "xrandr --newmode" then switch to that mode, using just "xrandr --output HDMI-A-0 --rate 144" does nothing: I believe the screen went black for a second then came back on but at 60 Hz.