I have been using Ubuntu 16.04LTS on this machine http://www.amazon.in/Lenovo-80NT00PAIN-15-6-inch-i7-6500U-Graphics/dp/B01B1AD32E/ for quite some tim.
It has a dedicated graphics unit AMD Radeon R7 M360 with 4GB memory, but it never showed up in the system settings. I always get the Intel chip as the graphics processer.

$ lspci -nn | grep VGA # Intel Corporation HD Graphics 520 [8086:1916]

I know amdgpu drivers in 16.04 do not support all the Radeon cards as of now, but I was hell bent on trying to make it work.
Found somewhere that it was related to outdated Linux Kernel. I was on 4.4.0-47-generic, so I updated to 4.6-*. I had kernel panics then, so I just reverted back to the previous kernel.
Then I tried with 4.8.6 stable release. The kernel worked, but still the same card. So I compiled the latest mesa drivers and installed.
Since I did that, I am stuck at the login screen. It never starts the X server. And I get this error in my syslog

[drm] PCIE GART of 4096M enabled (table at 0x0000000000040000)
[drm:gfx_v8_0_hw_init [amdgpu]] *ERROR* amdgpu: cp failed to lock ring (-2)
[drm:gfx_v8_0_ring_test_ring [amdgpu]] *ERROR* amdgpu: cp failed to lock ring 0 (-2)
[drm:amdgpu_resume [amdgpu]] *ERROR* resume 4 failed -2
[drm:amdgpu_resume_kms [amdgpu]] *ERROR* amdgpu_resume failed (-2)

I also get lightdm errors (I tried reconfiguring lightdm without success)

gnome-session-binary[12188]: CRITICAL: We failed, but the fail whale is dead. Sorry....
** (lightdm:1249): CRITICAL **: session_get_login1_session_id: assertion 'session != NULL' failed
[drm:amdgpu_sched_run_job [amdgpu]] *ERROR* Error scheduling IBs (-22)
[drm:amd_sched_main [amdgpu]] *ERROR* Failed to run job!