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I've installed ubuntu 19.10 on Lenovo Yoga S940 and it has some problems with refreshing the screen where it leaves multiple cursor traces when you move it, it doesn't redraw the input when you type something and similar stuff, so overall it creates a "laggish" impression (same on the preinstalled Windows btw, but this can be fixed there with some settings in the intel app).

What I've noticed is that when I boot from LifeUSB in safe graphics mode, everything works just perfect (well, except poweroff and suspension problems).

Seems like some graphic driver setting might cause the problem.

There are a lot of suggestions out there for similar problem but none of them worked for me so far and I'm wondering if anyone experienced this problem on this particular (or similar) configuration and might now a possible fix?

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Figured that finally out.

The problem was caused by Panel Self Refresh feature from intel. As described in this post:

Panel Self Refresh (PSR), a power saving feature used by Intel iGPUs is known to cause flickering in some instances FS#49628 FS#49371 FS#50605. A temporary solution is to disable this feature using the kernel parameter i915.enable_psr=0.

So to disable it and to fix the redraw problem without side effects (as far as I can tell as of now) I added it to kernel boot parameters (where i915 is the name of the loaded graphic driver):

i915.enable_psr=0

To do that, in terminal:

  1. sudo -i
  2. gedit /etc/default/grub
  3. locate the line that says GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
  4. change it to GRUB_CMDLINE_LINUX_DEFAULT="quiet splash i915.enable_psr=0"
  5. update-grub
  6. exit
  7. reboot

So as long as it's a "temporal" solution, I guess a permanent one would be to have the fix from intel. But as far as intel forum goes, this problem exists for at least 2 years already so seems like this one is permanent in reality.

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