[Intel-gfx] [PATCH] drm/i915/gem: Wait until the context is finally retired before releasing engines

[Chris Wilson]

If we want to percolate information back from the HW, up through the GEM
context, we need to wait until the intel_context is scheduled out for
the last time. This is handled by the retirement of the intel_context's
barrier, i.e. by listening to the pulse after the notional unpin. So
wait until the intel_context is finally retired before releasing the
engine, so that we can inspect the final context state and pass it on.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
---
 drivers/gpu/drm/i915/gem/i915_gem_context.c | 16 +++---
 drivers/gpu/drm/i915/i915_active.c          | 57 ++++++++++++++++++++-
 drivers/gpu/drm/i915/i915_active.h          |  3 +-
 3 files changed, 64 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index dffe0daee0d2..55f7879f6db4 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -570,23 +570,19 @@ static void engines_idle_release(struct i915_gem_context *ctx,
 	engines->ctx = i915_gem_context_get(ctx);
 
 	for_each_gem_engine(ce, engines, it) {
-		struct dma_fence *fence;
-		int err = 0;
+		int err;
 
 		/* serialises with execbuf */
 		set_bit(CONTEXT_CLOSED_BIT, &ce->flags);
 		if (!intel_context_pin_if_active(ce))
 			continue;
 
-		fence = i915_active_fence_get(&ce->timeline->last_request);
-		if (fence) {
-			err = i915_sw_fence_await_dma_fence(&engines->fence,
-							    fence, 0,
-							    GFP_KERNEL);
-			dma_fence_put(fence);
-		}
+		/* Wait until context is finally scheduled out and retired */
+		err = i915_sw_fence_await_active(&engines->fence,
+						 &ce->active,
+						 I915_ACTIVE_AWAIT_BARRIER);
 		intel_context_unpin(ce);
-		if (err < 0)
+		if (err)
 			goto kill;
 	}
 
diff --git a/drivers/gpu/drm/i915/i915_active.c b/drivers/gpu/drm/i915/i915_active.c
index 7b685032cc1e..c01bf25c8e5e 100644
--- a/drivers/gpu/drm/i915/i915_active.c
+++ b/drivers/gpu/drm/i915/i915_active.c
@@ -542,6 +542,54 @@ static int __await_active(struct i915_active_fence *active,
 	return 0;
 }
 
+struct wait_barrier {
+	struct wait_queue_entry base;
+	struct i915_active *ref;
+};
+
+static int
+barrier_wake(wait_queue_entry_t *wq, unsigned mode, int flags, void *key)
+{
+	struct wait_barrier *wb = container_of(wq, typeof(*wb), base);
+
+	if (i915_active_is_idle(wb->ref)) { /* shared waitqueue, must check! */
+		list_del(&wq->entry);
+		i915_sw_fence_complete(wq->private);
+		kfree(wq);
+	}
+
+	return 0;
+}
+
+static int __await_barrier(struct i915_active *ref, struct i915_sw_fence *fence)
+{
+	struct wait_barrier *wb;
+
+	wb = kmalloc(sizeof(*wb), GFP_NOWAIT | __GFP_NOWARN);
+	if (unlikely(!wb))
+		return -ENOMEM;
+
+	if (!i915_active_acquire_if_busy(ref)) {
+		kfree(wb);
+		return 0;
+	}
+
+	if (!i915_sw_fence_await(fence)) {
+		kfree(wb);
+		i915_active_release(ref);
+		return -EINVAL;
+	}
+
+	wb->base.flags = 0;
+	wb->base.func = barrier_wake;
+	wb->base.private = fence;
+
+	add_wait_queue(__var_waitqueue(ref), &wb->base);
+
+	i915_active_release(ref);
+	return 0;
+}
+
 static int await_active(struct i915_active *ref,
 			unsigned int flags,
 			int (*fn)(void *arg, struct dma_fence *fence),
@@ -556,7 +604,8 @@ static int await_active(struct i915_active *ref,
 			return err;
 	}
 
-	if (flags & I915_ACTIVE_AWAIT_ALL && i915_active_acquire_if_busy(ref)) {
+	if (flags & I915_ACTIVE_AWAIT_ACTIVE &&
+	    i915_active_acquire_if_busy(ref)) {
 		struct active_node *it, *n;
 
 		rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
@@ -569,6 +618,12 @@ static int await_active(struct i915_active *ref,
 			return err;
 	}
 
+	if (flags & I915_ACTIVE_AWAIT_BARRIER) {
+		err = __await_barrier(ref, arg);
+		if (err)
+			return err;
+	}
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/i915_active.h b/drivers/gpu/drm/i915/i915_active.h
index 4f9aa7bab514..c7d54d2302a2 100644
--- a/drivers/gpu/drm/i915/i915_active.h
+++ b/drivers/gpu/drm/i915/i915_active.h
@@ -193,7 +193,8 @@ int i915_sw_fence_await_active(struct i915_sw_fence *fence,
 int i915_request_await_active(struct i915_request *rq,
 			      struct i915_active *ref,
 			      unsigned int flags);
-#define I915_ACTIVE_AWAIT_ALL BIT(0)
+#define I915_ACTIVE_AWAIT_ACTIVE BIT(0)
+#define I915_ACTIVE_AWAIT_BARRIER BIT(1)
 
 int i915_active_acquire(struct i915_active *ref);
 bool i915_active_acquire_if_busy(struct i915_active *ref);
-- 
2.20.1