drm/i915/gt: Only wait for GPU activity before unbinding a GGTT fence

Only GPU activity via the GGTT fence is asynchronous, we know that we
control the CPU access directly, so we only need to wait for the GPU to
stop using the fence before we relinquish it.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200401210104.15907-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c

@@ -223,6 +223,11 @@ static void fence_write(struct i915_fence_reg *fence,
 	fence->dirty = false;
 }
 
+static bool gpu_uses_fence_registers(struct i915_fence_reg *fence)
+{
+	return INTEL_GEN(fence_to_i915(fence)) < 4;
+}
+
 static int fence_update(struct i915_fence_reg *fence,
 			struct i915_vma *vma)
 {
@@ -239,15 +244,18 @@ static int fence_update(struct i915_fence_reg *fence,
 		if (!i915_vma_is_map_and_fenceable(vma))
 			return -EINVAL;
 
+		if (gpu_uses_fence_registers(fence)) {
+			/* implicit 'unfenced' GPU blits */
 			ret = i915_vma_sync(vma);
 			if (ret)
 				return ret;
 		}
+	}
 
 	old = xchg(&fence->vma, NULL);
 	if (old) {
 		/* XXX Ideally we would move the waiting to outside the mutex */
-		ret = i915_vma_sync(old);
+		ret = i915_active_wait(&fence->active);
 		if (ret) {
 			fence->vma = old;
 			return ret;
@@ -869,6 +877,7 @@ void intel_ggtt_init_fences(struct i915_ggtt *ggtt)
 	for (i = 0; i < num_fences; i++) {
 		struct i915_fence_reg *fence = &ggtt->fence_regs[i];
 
+		i915_active_init(&fence->active, NULL, NULL);
 		fence->ggtt = ggtt;
 		fence->id = i;
 		list_add_tail(&fence->link, &ggtt->fence_list);
@@ -880,6 +889,14 @@ void intel_ggtt_init_fences(struct i915_ggtt *ggtt)
 
 void intel_ggtt_fini_fences(struct i915_ggtt *ggtt)
 {
+	int i;
+
+	for (i = 0; i < ggtt->num_fences; i++) {
+		struct i915_fence_reg *fence = &ggtt->fence_regs[i];
+
+		i915_active_fini(&fence->active);
+	}
+
 	kfree(ggtt->fence_regs);
 }
 

drivers/gpu/drm/i915/gt/intel_ggtt_fencing.h

@@ -28,6 +28,8 @@
 #include <linux/list.h>
 #include <linux/types.h>
 
+#include "i915_active.h"
+
 struct drm_i915_gem_object;
 struct i915_ggtt;
 struct i915_vma;
@@ -41,6 +43,7 @@ struct i915_fence_reg {
 	struct i915_ggtt *ggtt;
 	struct i915_vma *vma;
 	atomic_t pin_count;
+	struct i915_active active;
 	int id;
 	/**
 	 * Whether the tiling parameters for the currently

drivers/gpu/drm/i915/i915_vma.c

@@ -1232,6 +1232,10 @@ int i915_vma_move_to_active(struct i915_vma *vma,
 		dma_resv_add_shared_fence(vma->resv, &rq->fence);
 		obj->write_domain = 0;
 	}
+
+	if (flags & EXEC_OBJECT_NEEDS_FENCE && vma->fence)
+		i915_active_add_request(&vma->fence->active, rq);
+
 	obj->read_domains |= I915_GEM_GPU_DOMAINS;
 	obj->mm.dirty = true;