+ *
+ * Return:
+ * 0 on success, or an error on failing to expand the array.
+ */
+int drm_sched_job_prealloc_dependency_slots(struct drm_sched_job
*job,
+					    unsigned int num_deps)
+{
+	struct dma_fence *fence;
+	u32 id = 0;
+	int ret;
+
+	while (num_deps--) {
+		fence = dma_fence_get_stub();
+		ret = xa_alloc(&job->dependencies, &id, fence,
xa_limit_32b,
+			       GFP_KERNEL);

So this would fill the xarr with already signaled fences which then
later will be replaced with unsignaled fences?

Yes, exactly that's the idea.

Help me out here: would it also work to add NULL instead of that stub-
fence?

Good question, idk. That's an implementation detail of the xarray.

Tvrtko also correctly pointed out that it is most likely a bad idea to use dma_fence_is_signaled() in the critical code path.

I will try to dig through the xarray behavior up and update the patch if possible.

Thanks,
Christian.