Comment 61 for bug 1570653

If you want to build your own kernel, you can get the source from https://launchpad.net/ubuntu/+source/linux/4.4.0-47.68

Have a look at the file drivers/gpu/drm/radeon/si_dpm.c
Use the following commit as an example https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=ea039f927524e36c15b5905b4c9469d788591932

Note the line _above_ the line in green. That is your graphics card. Try changing it from

{ PCI_VENDOR_ID_ATI, 0x6811, 0x174b, 0xe271, 0, 120000 }

to

{ PCI_VENDOR_ID_ATI, 0x6811, 0x174b, 0xe271, 85000, 90000 }

and also try removing that line altogether.