Comment 31 for bug 1542939

This bug affects the 4.4 kernel, including the xenial kernel and the lts-xenial kernel in trusty.

The linked freedesktop bug report mentions that the bug was fixed in the 4.5 kernel with the following commit,

http://kernel.ubuntu.com/git/ubuntu/linux.git/commit/?id=92826fcdfc147a7d16766e987c12a9dfe1860c3f

The commit was not backported to the 4.4 kernel, and is not present in the xenial kernel.

I initially tested the 4.5 mainline kernel and found that it does fix the bug.

I then attempted to apply the aforementioned commit to the xenial kernel and found that it does not apply cleanly. By including two earlier patches I was able to get it to apply (with minor porting). But the resultant kernel did not fix the bug.

Details:
The two earlier patches are:

drm/i915/ivb: Move WaCxSRDisabledForSpriteScaling w/a to atomic check, d21fbe87ce18297af0a9b7cc0cd545fd9ac28d33

drm/i915: Move disable_cxsr to the crtc_state,
ab1d3a0e5a44f5b1a8d1f811e925c8519b56fba4