[Intel-gfx] [PATCH 01/16] drm/i915: Introduce i915_gem_active_wait_unlocked()

[Chris Wilson]

It is useful to be able to wait on pending rendering without grabbing
the struct_mutex. We can do this by using the i915_gem_active_get_rcu()
primitive to acquire a reference to the pending request without
requiring struct_mutex, just the RCU read lock, and then call
i915_wait_request().

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_request.h | 36 +++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
index 48382ac401fd..d077b023a89f 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.h
+++ b/drivers/gpu/drm/i915/i915_gem_request.h
@@ -546,6 +546,42 @@ i915_gem_active_wait(const struct i915_gem_active *active, struct mutex *mutex)
 }
 
 /**
+ * i915_gem_active_wait_unlocked - waits until the request is completed
+ * @active - the active request on which to wait
+ * @interruptible - whether the wait can be woken by a userspace signal
+ * @timeout - how long to wait at most
+ * @rps - userspace client to charge for a waitboost
+ *
+ * i915_gem_active_wait_unlocked() waits until the request is completed before
+ * returning, without requiring any locks to be held. Note that it does not
+ * retire any requests before returning.
+ *
+ * This function wraps i915_wait_request(), see it for the full details.
+ *
+ * Returns 0 if successful, or a negative error code.
+ */
+static inline int
+i915_gem_active_wait_unlocked(const struct i915_gem_active *active,
+			      bool interruptible,
+			      s64 *timeout,
+			      struct intel_rps_client *rps)
+{
+	struct drm_i915_gem_request *request;
+	int ret = 0;
+
+	rcu_read_lock();
+	request = i915_gem_active_get_rcu(active);
+	rcu_read_unlock();
+
+	if (request) {
+		ret = i915_wait_request(request, interruptible, timeout, rps);
+		i915_gem_request_put(request);
+	}
+
+	return ret;
+}
+
+/**
  * i915_gem_active_retire - waits until the request is retired
  * @active - the active request on which to wait
  *
-- 
2.8.1