CONFIG_DRM_TTM is used by many DRM drivers. It is now does not have name in Kconfig, so it only could be autoselected by other drivers. User can't select it with "menu menuconfig" Virtualbox driver (vboxvideo) uses it, so when I compile new kernel I can't enable this option unless I enable any other driver that I do not need. I suggest to give it a name, for example "GPU TTM". I can create patch for that:)
Sounds rather like vboxvideo needs to autoselect TTM as well.
Virtualbox is not part of Linux source tree. Threre is an .iso file for each VBox version that contains sources and script to compile it against your kernel
Arguably not a bug in kernel.
Not a bug at all. I'd call it "usability problem") User can't enable TTM (which is required for virtualbox) unless she enables some redundant driver.