Created attachment 60762 [details] kernel log of oopses. Trying to switch to the Discrete Radeon 0x6740 adaptor from the integrated Intel Sandybridge causes kernel oops. This happened on a DV7-6015tx. Interestingly the oops seemed to cause my running ssh session froze, and I couldn't establish another ssh session, but it the laptop did appear to obey either ctrl-alt-delete or the power-button and proceeded to shut down.
Created attachment 60772 [details] lspci -vvv output
Sorry should have mentioned it happened on a Hewlett Packard Pavilion DV7-6015tx laptop (17.3" Widescreen with after market ram upgrade to 8GB and Intel 160GB MLC SSD. Also, to clarify, the order of events was: 1) issued "echo DDIS > /sys/kernel/debug/vgaswitcheroo/switch" in ssh remote terminal. 2) issued "/etc/init.d/gdm3 restart" 3) gdm shutdown and the lcd screen went blank and my ssh session froze. 4) attempted to establish another ssh session. This failed too. 5) attempted ctrl-alt-delete followed by pressing the power button. I currently only have remote (ssh) access to the machine and rely on others to be the eyes and ears. I'm trying to get the ability to switch between the Integrated intel graphics and the Discrete AMD/ATI radeon graphics devices. Keen to help debug this further. Daniel.
I'm gonna blame radeon on this one ;-) Especially since the hang seems to only happen when we start rendering on the radeon gpu (gdm3 starting), and at that point drm/i915 shouldn't interfere with anything anymore at all ...
Most recent hybrid laptops are muxless so the laptop panel is not actually connected to the discrete chip. Most likely X is failing to start on radeon since the are no connected displays. The only way to support these systems is with fairly major changes to the X server to support decoupled display and rendering. Work has begun on these changes, but they are not ready for end users yet. Can you attach your full dmesg and xorg log after trying to switch to radeon?