[nvidia] Display content "overflows" when using Xorg fractional scaling

[Bin Li]

On ThinkStation with Nvidia T400.

1. Enter os,and enter Settings -> Displays
2. Change the Scale from 100% to 200% and aplly keep changes
3. Turn on the Fractional scaling
4. Turn off the Fractional scaling
5. Turn on and off again and again, each time the screen size is doubled.

Screen 0: minimum 8 x 8, current 1920 x 1080, maximum 32767 x 32767

Screen 0: minimum 8 x 8, current 3840 x 2160, maximum 32767 x 32767

Screen 0: minimum 8 x 8, current 7680 x 4320, maximum 32767 x 32767

[Bin Li (binli)]

When I did below operation it could show the full desktop.

For 3840 x 2160
$ xrandr --output DP-5 --scale 2x2

For 7680 x 4320
$ xrandr --output DP-5 --scale 4x4

[Daniel van Vugt (vanvugt)]

See also bug 1942653. Maybe also bookmark https://bugs.launchpad.net/ubuntu/+bugs?field.tag=xrandr-scaling.

[Bin Li (binli)]

@daniel,

 Thanks, I will verify that patch, reply you later.

[Daniel van Vugt (vanvugt)]

The patch is what you're already using to get fractional scaling in Xorg sessions. There is nothing to test or verify.

But we know it has issues (https://bugs.launchpad.net/ubuntu/+bugs?field.tag=xrandr-scaling) and so defaulting to Wayland, even for Nvidia, in jammy is a priority. Because Wayland sessions support fractional scaling without using the patch.

[jeremyszu (os369510)]

This issue comes from OEM partner which certifying with Ubuntu 20.04.
We may still need to consider a fix in X for 20.04 or switching to X from gdm in 22.04.