Just tested Kernel 4.0-rc1 – announced here:  http://lkml.iu.edu/hypermail/linux/kernel/1502.2/04059.html

As you will see – not much actual detail on what has changed, and I have already run into a couple of ‘issues’…

The Radeon drm driver on my laptop refuses to load, and the boot hangs immediately with

drm r600_ring_test [radeon] *ERROR* radeon: ring 0 test failed (scratch(0x8504)=0xFFFFFFFF)
radeon 0000:01:00.0: disabling GPU acceleration

The workaround is to disable the drm driver, and just use the framebuffer one, for the time being..

VMware 11.1.0 – with the vmnet patches – loads and runs OK..

NVIDIA driver 346.35 fails to compile:

/home/rgadsdon/NVIDIA-Linux-x86_64-346.35/kernel/nv-pat.c: In function ‘nv_disable_caches’:
/home/rgadsdon/NVIDIA-Linux-x86_64-346.35/kernel/nv-pat.c:38:5: error: implicit declaration of function ‘read_cr4’ [-Werror=implicit-function-declaration]
 *cr4 = read_cr4();
 ^
/home/rgadsdon/NVIDIA-Linux-x86_64-346.35/kernel/nv-pat.c:39:5: error: implicit declaration of function ‘write_cr4’ [-Werror=implicit-function-declaration]
 if (*cr4 & 0x80) write_cr4(*cr4 & ~0x80);
 ^
cc1: some warnings being treated as errors

Thanks to juston_li at the NVIDIA DevZone forums, there is a simple fix, but the example is – as is mentioned – only for 4.0 and later, and needs to have kernel version tests added, to leave the code as-is for pre-4.0 kernels..

https://devtalk.nvidia.com/default/topic/813458/linux/linux-4-0-rc1-346-35-build-error-_cr4-functions-fix/

More test are needed, but at least it booted OK, after the above ‘workarounds’..

$ uname -a
Linux rg6830l 4.0.0-rc1 #1 SMP Sun Feb 22 23:51:39 PST 2015 x86_64 x86_64 x86_64 GNU/Linux

Robert Gadsdon.   February 22, 2015.