On Fri, Dec 09, 2016 at 02:56:56PM +0100, Daniel Vetter wrote:
We thought that no userspace is using them, but oops libdrm is using them to figure out whether a driver supports modesetting. Check out drmCheckModesettingSupported but maybe don't because it's horrible and totally runs counter to where we want to go with libdrm device handling. The function looks in the device hierarchy for whether controlD* exist using the following format string:
/sys/bus/pci/devices/%04x:%02x:%02x.%d/drm/controlD%d
The "/drm" subdirectory is the glue directory from the sysfs class stuff, and the only way to get at it seems to through kdev->kobj.parent (when kdev is represents e.g. the card0 chardev instance in sysfs). Git grep says we're not the only ones touching that, so I hope it's ok we dig into such internals - I couldn't find a proper interface for getting at the glue directory.
Quick git grep shows that at least -amdgpu, -ati are using this. -modesetting do not, and on -intel it's only about the 4th fallback path for device lookup, which is why this didn't blow up earlier.
Oh well, we need to keep it working, and the simplest way is to add a symlink at the right place in sysfs from controlD* to card*.
v2:
- Fix error path handling by adding if (!minor) return checks (David)
- Fix the controlD* numbers to match what's been there (David)
- Add a comment what exactly userspace minimally needs.
- Correct the analysis for -intel (Chris).
Fixes: 8a357d10043c ("drm: Nerf DRM_CONTROL nodes") Cc: Dave Airlie airlied@gmail.com Reported-by: Alex Deucher alexander.deucher@amd.com Cc: Alex Deucher alexander.deucher@amd.com Cc: David Herrmann dh.herrmann@gmail.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com
Acked-by: Greg Kroah-Hartman gregkh@linuxfoundation.org