https://bugzilla.kernel.org/show_bug.cgi?id=75401
Bug ID: 75401 Summary: vgaswtitcheroo doesn't work for AMD Radeon 8870m (possibly due to "wrong" PCI class) Product: Drivers Version: 2.5 Kernel Version: 3.11.10 Hardware: All OS: Linux Tree: Mainline Status: NEW Severity: low Priority: P1 Component: Video(DRI - non Intel) Assignee: drivers_video-dri@kernel-bugs.osdl.org Reporter: drill87@gmail.com Regression: No
I've got Samsung 870Z5E notebook equipped with AMD Radeon 8870m video card (and Intel HD 4000 graphics). I always failed to use vgaswitcheroo to disable the discrete card -- there wasn't even its entry in debugfs.
After a little investigetion of radeon module's source code I found, that the problem happens, possibly, due to "unusual" PCI class of my Radeon 8870m. According to command "lspci -nn" Radeon 8870m has PCI class id 0380, which is corresponds to PCI_CLASS_DISPLAY_OTHER (in pci_ids.h). On the other hand, when radeon module check number of videocards, it excepts them to have class PCI_CLASS_DISPLAY_VGA (0300). Thus module concludes that I have only 1 videocard (Intel HD, which has 0300 class id) and decides, that there's no need for vgaswitcheroo to be initialized.
I tried to edit radeon kernel module by adding additional checks for PCI_CLASS_DISPLAY_OTHER class id (in 2 places). After that vgaswitcheroo started to work -- the entry appeared in debugfs and I could disable the discrete graphics card. Though I'm not sure if everything went right because I failed to use radeon card for actual rendering through DRI PRIME even in the newest kernel stable version (3.14.2) -- X server crashes even if I try to issues glxinfo command.