drm/i915/selftests: Set vm->gt backpointer for mock_ppgtt

Add the backpointer to ppgtt and i915->gt so that we can traverse across
the device hierarchy.
Reported-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191022095851.23442-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/selftests/mock_gem_device.c

@@ -181,6 +181,7 @@ struct drm_i915_private *mock_gem_device(void)
 	intel_timelines_init(i915);
 
 	mock_init_ggtt(i915, &i915->ggtt);
+	i915->gt.ggtt = &i915->ggtt;
 
 	mkwrite_device_info(i915)->engine_mask = BIT(0);
 

drivers/gpu/drm/i915/selftests/mock_gtt.c

@@ -63,6 +63,7 @@ struct i915_ppgtt *mock_ppgtt(struct drm_i915_private *i915, const char *name)
 	if (!ppgtt)
 		return NULL;
 
+	ppgtt->vm.gt = &i915->gt;
 	ppgtt->vm.i915 = i915;
 	ppgtt->vm.total = round_down(U64_MAX, PAGE_SIZE);
 	ppgtt->vm.file = ERR_PTR(-ENODEV);