Comment 6 for bug 1928138

Trying to find the reason for this issue I tested kernels from https://kernel.ubuntu.com/~kernel-ppa/mainline/ on Ubuntu 14.04

v4.0.9-wily - flickering didn't happen (but that's because DRRS wasn't activated in the 4.0.y series)
v4.1-rc3-unstable - problem started here.

So it's quite possible that on a particular machine this issue is present since v4.1-rc1

I found that this is DRRS by looking at i915 commits in the 4.1.y tree.
https://github.com/gregkh/linux/commits/linux-4.1.y/drivers/gpu/drm/i915/
intel_pc.c and intel_display.c have some DRRS-related changes

I can try to revert some commits from there.
Some interesting commits:
* drm/i915: Add support for DRRS in intel_dp_set_m_n
(https://github.com/gregkh/linux/commit/fe3cd48d6b616efc76b6a4003e82e933618c788a#diff-83261d1489be7f0a6d1b8306ff0fddbeb13ceb74768ea99274b009dce13ffd2e)
* drm/i915/bdw: Add support for DRRS to switch RR
(https://github.com/gregkh/linux/commit/a4c30b1d108c1ef60667ed357af4aeabc3d05eca#diff-83261d1489be7f0a6d1b8306ff0fddbeb13ceb74768ea99274b009dce13ffd2e)