Early Intel Skylake Linux Users May Run Into A Silly Issue
Earlier today I wrote about the Intel Core i5 6600K "Skylake" running fine on Ubuntu Linux compared to the issues encountered when running the i7-5775C Broadwell processor. This Intel Skylake CPU is running fine so far on Linux but there is a minor workaround that many users will experience if upgrading to a Skylake processor in the next few months.
When installing Fedora 22 or switching away from the default kernel on Ubuntu 15.04 (say to the current Linux 4.2 mainline kernel PPA) or run likely any other modern distribution out there, you won't get kernel mode-setting support and working 3D acceleration for Skylake's HD Graphics... You'll get a low resolution display and fall-back to the LLVMpipe Gallium3D driver. Yes, even with modern kernels.
This issue is due to Skylake being considered of "preliminary hardware support" by the Intel DRM kernel driver. Skylake still falls under this "feature" introduced in 2012 where Intel is hiding early support for new hardware by default until it's stabilized.
So when booting Fedora 22 out-of-the-box or upgrading on Ubuntu to the latest mainline kernel (they're stock kernel avoids this issue) you need to append to your kernel command-line: i915.preliminary_hw_support=1. When adding that to your kernel command-line in GRUB (or editing your GRUB configuration for it to be persistent) the i915 DRM driver initialized fine on these kernels and lit up the i5-6600K's HD Graphics 530 just fine. With Linux 3.19, 4.0, and 4.2 are the kernels tested so far.
This is the first time where at the release of a new Intel hardware platform I've run into this problem running a modern kernel... I have to wonder whether this preliminary hardware support flag makes sense or leads to a better user experience. While having preliminary hardware support there by default could lead to some display-related issues, if the user hits such problems, they could always just pass nomodeset to the kernel command-line. Instead the default behavior is no preliminary hardware support whereby instead you get a low resolution display (and LLVMpipe software acceleration). So far this "preliminary" hardware support seems fine. On an unrelated note, in Mesa 11.0-devel Git with the i5-6600K HD Graphics I have encountered some hangs that are regressions compared to Mesa 10.5~10.6.
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