drm/i915: Re-arrange execbuf so context is known before engine

Needed for a following patch.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190301140404.26690-23-chris@chris-wilson.co.ukSigned-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_gem_execbuffer.c

@@ -2312,10 +2312,6 @@ i915_gem_do_execbuffer(struct drm_device *dev,
 	if (args->flags & I915_EXEC_IS_PINNED)
 		eb.batch_flags |= I915_DISPATCH_PINNED;
 
-	eb.engine = eb_select_engine(eb.i915, file, args);
-	if (!eb.engine)
-		return -EINVAL;
-
 	if (args->flags & I915_EXEC_FENCE_IN) {
 		in_fence = sync_file_get_fence(lower_32_bits(args->rsvd2));
 		if (!in_fence)
@@ -2340,6 +2336,12 @@ i915_gem_do_execbuffer(struct drm_device *dev,
 	if (unlikely(err))
 		goto err_destroy;
 
+	eb.engine = eb_select_engine(eb.i915, file, args);
+	if (!eb.engine) {
+		err = -EINVAL;
+		goto err_engine;
+	}
+
 	/*
 	 * Take a local wakeref for preparing to dispatch the execbuf as
 	 * we expect to access the hardware fairly frequently in the
@@ -2505,6 +2507,7 @@ i915_gem_do_execbuffer(struct drm_device *dev,
 	mutex_unlock(&dev->struct_mutex);
 err_rpm:
 	intel_runtime_pm_put(eb.i915, wakeref);
+err_engine:
 	i915_gem_context_put(eb.ctx);
 err_destroy:
 	eb_destroy(&eb);