Ubuntu: Hibernate/Suspend to disk: Resume problem with ATI Radeon R7

On a new Lenovo laptop i had some issues with supsend/resume.
I installed tux on ice and the suspend process worked, but the resume just freezed after some seconds.

First step to solve this problem was to stop the graphics (/etc/init.d/lightdm stop) and try it again.

This attempt worked without a problem, so it was clear: the resume problem is a issue with the graphic card:

laptop:~$ lspci
[...]
01:00.0 Display controller: Advanced Micro Devices, Inc. [AMD/ATI] Topaz XT [Radeon R7 M260/M265] (rev ff9)
[...]

So i tried to disable the modesettings with grub. I changed in /etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sda9 quiet splash"

to

 GRUB_CMDLINE_LINUX_DEFAULT="resume=/dev/sda9 quiet splash  nomodeset"

and then the command

update-grub

And after that everything worked...



Here an explanation from https://ubuntuforums.org/showthread.php?t=1613132:
nomodeset
The newest kernels have moved the video mode setting into the kernel. So all the programming of the hardware specific clock rates and registers on the video card happen in the kernel rather than in the X driver when the X server starts.. This makes it possible to have high resolution nice looking splash (boot) screens and flicker free transitions from boot splash to login screen. Unfortunately, on some cards this doesnt work properly and you end up with a black screen. Adding the nomodeset parameter instructs the kernel to not load video drivers and use BIOS modes instead until X is loaded.

Note that this option is sometimes needed for nVidia cards when using the default "nouveau" drivers. Installing proprietary nvidia drivers usually makes this option no longer necessary, so it may not be needed to make this option permanent, just for one boot until you installed the nvidia drivers.