vgaswitcheroo is not working on kernel 3.12 because /sys/kernel/debug/vgaswitcheroo is missing. As a consequence, it is not possible to control the discrete graphics card.
This seems to be due to a driver conflict between shpchp and another pci acpi hotplug driver (which is compiled into the kernel by default). Recompiling the kernel with
# CONFIG_HOTPLUG_PCI_ACPI is not set
fixes the issue (see comment 13 in linked bug report).
Affected packages: kernel-3.12.5-302.fc20.x86_64 and earlier 3.12 kernels
Was working fine on 2.11 kernel (Fedora 19).
At least this patch seems to be needed. Although I am not 100% sure it will be enough:
Can you give the patch a try and report back?
I'm away for a couple of days, I'll test the patch when I'm back. Thanks!
Created attachment 845836 [details]
patch from https://lkml.org/lkml/2013/12/31/162 changed for kernel 3.12.6
I patched kernel 3.12.6 with the patch you provided and /sys/kernel/debug/vgaswitcheroo is now present and works as expected.
I had to slightly change the patch so it would apply to 3.12.6 so I attached the new patch.
Perfect. Thanks for testing. I'll let the kernel team see if it makes
sense picking it up before it trickles down via linux-stable.
Greg is working on importing patches for 3.12.7 right now. Let's wait for a couple days and see if he grabs this one and includes it. If not, we can apply it ourselves.
3.12.7 is in updates-testing now.
Works with kernel 3.12.7 which is now available through updates.