drm/i915: Introduce a context barrier callback

In the next patch, we will want to update live state within a context.
As this state may be in use by the GPU and we haven't been explicitly
tracking its activity, we instead attach it to a request we send down
the context setup with its new state and on retiring that request
cleanup the old state as we then know that it is no longer live.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190309160250.29324-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -677,6 +677,80 @@ last_request_on_engine(struct i915_timeline *timeline,
 	return NULL;
 }
 
+struct context_barrier_task {
+	struct i915_active base;
+	void (*task)(void *data);
+	void *data;
+};
+
+static void cb_retire(struct i915_active *base)
+{
+	struct context_barrier_task *cb = container_of(base, typeof(*cb), base);
+
+	if (cb->task)
+		cb->task(cb->data);
+
+	i915_active_fini(&cb->base);
+	kfree(cb);
+}
+
+I915_SELFTEST_DECLARE(static unsigned long context_barrier_inject_fault);
+static int context_barrier_task(struct i915_gem_context *ctx,
+				unsigned long engines,
+				void (*task)(void *data),
+				void *data)
+{
+	struct drm_i915_private *i915 = ctx->i915;
+	struct context_barrier_task *cb;
+	struct intel_context *ce;
+	intel_wakeref_t wakeref;
+	int err = 0;
+
+	lockdep_assert_held(&i915->drm.struct_mutex);
+	GEM_BUG_ON(!task);
+
+	cb = kmalloc(sizeof(*cb), GFP_KERNEL);
+	if (!cb)
+		return -ENOMEM;
+
+	i915_active_init(i915, &cb->base, cb_retire);
+	i915_active_acquire(&cb->base);
+
+	wakeref = intel_runtime_pm_get(i915);
+	list_for_each_entry(ce, &ctx->active_engines, active_link) {
+		struct intel_engine_cs *engine = ce->engine;
+		struct i915_request *rq;
+
+		if (!(ce->engine->mask & engines))
+			continue;
+
+		if (I915_SELFTEST_ONLY(context_barrier_inject_fault &
+				       engine->mask)) {
+			err = -ENXIO;
+			break;
+		}
+
+		rq = i915_request_alloc(engine, ctx);
+		if (IS_ERR(rq)) {
+			err = PTR_ERR(rq);
+			break;
+		}
+
+		err = i915_active_ref(&cb->base, rq->fence.context, rq);
+		i915_request_add(rq);
+		if (err)
+			break;
+	}
+	intel_runtime_pm_put(i915, wakeref);
+
+	cb->task = err ? NULL : task; /* caller needs to unwind instead */
+	cb->data = data;
+
+	i915_active_release(&cb->base);
+
+	return err;
+}
+
 int i915_gem_switch_to_kernel_context(struct drm_i915_private *i915,
 				      unsigned long mask)
 {

drivers/gpu/drm/i915/selftests/i915_gem_context.c

@@ -1594,10 +1594,116 @@ static int igt_switch_to_kernel_context(void *arg)
 	return err;
 }
 
+static void mock_barrier_task(void *data)
+{
+	unsigned int *counter = data;
+
+	++*counter;
+}
+
+static int mock_context_barrier(void *arg)
+{
+#undef pr_fmt
+#define pr_fmt(x) "context_barrier_task():" # x
+	struct drm_i915_private *i915 = arg;
+	struct i915_gem_context *ctx;
+	struct i915_request *rq;
+	intel_wakeref_t wakeref;
+	unsigned int counter;
+	int err;
+
+	/*
+	 * The context barrier provides us with a callback after it emits
+	 * a request; useful for retiring old state after loading new.
+	 */
+
+	mutex_lock(&i915->drm.struct_mutex);
+
+	ctx = mock_context(i915, "mock");
+	if (IS_ERR(ctx)) {
+		err = PTR_ERR(ctx);
+		goto unlock;
+	}
+
+	counter = 0;
+	err = context_barrier_task(ctx, 0, mock_barrier_task, &counter);
+	if (err) {
+		pr_err("Failed at line %d, err=%d\n", __LINE__, err);
+		goto out;
+	}
+	if (counter == 0) {
+		pr_err("Did not retire immediately with 0 engines\n");
+		err = -EINVAL;
+		goto out;
+	}
+
+	counter = 0;
+	err = context_barrier_task(ctx,
+				   ALL_ENGINES, mock_barrier_task, &counter);
+	if (err) {
+		pr_err("Failed at line %d, err=%d\n", __LINE__, err);
+		goto out;
+	}
+	if (counter == 0) {
+		pr_err("Did not retire immediately for all inactive engines\n");
+		err = -EINVAL;
+		goto out;
+	}
+
+	rq = ERR_PTR(-ENODEV);
+	with_intel_runtime_pm(i915, wakeref)
+		rq = i915_request_alloc(i915->engine[RCS0], ctx);
+	if (IS_ERR(rq)) {
+		pr_err("Request allocation failed!\n");
+		goto out;
+	}
+	i915_request_add(rq);
+	GEM_BUG_ON(list_empty(&ctx->active_engines));
+
+	counter = 0;
+	context_barrier_inject_fault = BIT(RCS0);
+	err = context_barrier_task(ctx,
+				   ALL_ENGINES, mock_barrier_task, &counter);
+	context_barrier_inject_fault = 0;
+	if (err == -ENXIO)
+		err = 0;
+	else
+		pr_err("Did not hit fault injection!\n");
+	if (counter != 0) {
+		pr_err("Invoked callback on error!\n");
+		err = -EIO;
+	}
+	if (err)
+		goto out;
+
+	counter = 0;
+	err = context_barrier_task(ctx,
+				   ALL_ENGINES, mock_barrier_task, &counter);
+	if (err) {
+		pr_err("Failed at line %d, err=%d\n", __LINE__, err);
+		goto out;
+	}
+	mock_device_flush(i915);
+	if (counter == 0) {
+		pr_err("Did not retire on each active engines\n");
+		err = -EINVAL;
+		goto out;
+	}
+
+out:
+	mock_context_close(ctx);
+unlock:
+	mutex_unlock(&i915->drm.struct_mutex);
+	return err;
+#undef pr_fmt
+#define pr_fmt(x) x
+}
+
 int i915_gem_context_mock_selftests(void)
 {
 	static const struct i915_subtest tests[] = {
 		SUBTEST(igt_switch_to_kernel_context),
+		SUBTEST(mock_context_barrier),
 	};
 	struct drm_i915_private *i915;
 	int err;