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I am new to this forum and i apologize if this has been already answered and sorry if the i couldn't explain it better but I need help with using a custom resolution for my monitor in Ubuntu(19.10) linux.

My monitor is a bit damaged i guess and cannot output at 1080p 60hz (but somehow can @65hz and 62hz) so in my windows i used amd's custom resolution setting to apply a 65 and 62hz refresh rate (which work flawlessly) at 1080p on windows. On linux I used both cvt and gtf commands to output a modeline and use it with xrandr but none work. I'm trying to figure out what exact settings does the amd driver put to make the monitor work, and some settings it does provide info on I can't seem to make them work on linux. Here are the settings i took from the amd radeon settings on windows I hope they can be of help:

-Horizontal Res: 1920px -Vertical res: 1080px -Refresh rate: 62Hz -Progressive

-Timing Standard:Manual G.Pixel Clock:153450(kHz) G.Refresh Rate: 62.000(Hz)

H.Timing Total: 2200 H.Timing Display: 1920 H.Timing Front Porch: 88 H.Timing sync Width: 44

V.Timing Total: 1125 V.Timing Display: 1080 V.Timing Front Porch: 4 V.Timing sync Width: 5

H.Timing Polarity && V.Timing Polarity are Positive

These are the the settings i guess that work on windows but I can't seem to be able to use this on linux. If someone can help me be able to use this or maybe knows how to get more info on windows that would be greatly appreciated

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I'm no expert, but I think you can achieve this custom resolution/refresh rate with the following steps:

1. Get the modeline

For this, you will have to install a software called umc Universal Modeline Calculator. Sadly this software isn't available through the repositories so you have to install it manually. Download the latest version and follow the install steps found in the INSTALL file (duh) ... or you could copy-paste the following commands if you trust me already:

tar -zxvf umc-0.2.tar.gz
cd umc-0.2/
./configure
make
sudo make install

If correctly installed, you should see an output like this if you type umc in the console:

Try `umc --help' for more information.

Now open the terminal and type umc to get the actual modeline that will work with your monitor and GPU.

$ umc <width> <height> <refresh rate> --rbt

For you it'll be something like this:

$ umc 1920 1080 62 --rbt

It will probably output something like this:

    # 1920x1080x61.99 @ 63.915kHz
    Modeline "1920x1080x61.99"  [a bunch of numbers] +HSync -VSync
Side note: I found that the reason of this working in this thread.

Using the cvt utility to generate a reduced blanking mode only works for refresh rates that are multiples of 60. I used umc (univesal modeline calculator - not available through the repositories) to generate this mode.

2. Define modeline

Copy the line after the word Modeline of the previous output and then use xrandr to add a new mode:

xrandr --newmode "1920x1080x61.99"  [a bunch of numbers] +HSync -VSync

3. Add mode to monitor

Then use xrandr again to add the mode to your current monitor.

Side note:

If you don't know the identifier of your monitor check xrandr output for the words before connected primary. For me it is HDMI-A-0 since my monitor is connected via HDMI.

xrandr --addmode <monitor> 1920x1080x61.99

4. Change mode

After this was successful we then can switch to this new mode.

BUT FIRST let's have a backup plan if anything goes wrong.

Type in the following command but we use the current mode.

xrandr --output <monitor> --mode <current mode>

Then we can run the command but with the desired mode:

xrandr --output <monitor> --mode 1920x1080x61.99

This way, if ─ for example ─ your screen turns black and you can't see anything, press the up arrow (), and then enter () you should be able to switch to the mode that was working before.

If that doesn't work. Try the old trick: unplugging (your monitor) and plugging again. It usually works. LOL. Now seriously, you should follow this steps carefully. At this point, I don't know if changing any values of the modeline will help, I wouldn't recommend doing that, so I really hope that you can make your monitor work with the steps above.


Sources of inspiration:

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