Comment 15 for bug 1114370

ppa:mainline is not strictly a repo, but an archive of daily snapshots of the upstream kernel. They don't want to make it a repo to avoid the kernel and inadvertent breakage. Hmm, seems it is out of date. You can just clone the upstream kernel, pull in drm-intel-next and build that using your ubuntu config, all it takes is a little bit of time.

I don't think there is a fix in there, which it makes it even more important that you can build upstream kernels so that you can apply patches to test.