drm/i915: Disable waitboosting for fence_wait()

We want to restrict waitboosting to known process contexts, where we can
track which clients are receiving waitboosts and prevent excessive power
wasting. For fence_wait() we do not have any client tracking and so that
leaves it open to abuse.

v2: Hide the IS_ERR_OR_NULL testing for special clients
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469002875-2335-5-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_request.c

@@ -70,7 +70,7 @@ static signed long i915_fence_wait(struct fence *fence,
 
 	ret = __i915_wait_request(to_request(fence),
 				  interruptible, timeout,
-				  NULL);
+				  NO_WAITBOOST);
 	if (ret == -ETIME)
 		return 0;
 
@@ -642,7 +642,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	 * forcing the clocks too high for the whole system, we only allow
 	 * each client to waitboost once in a busy period.
 	 */
-	if (INTEL_GEN(req->i915) >= 6)
+	if (IS_RPS_CLIENT(rps) && INTEL_GEN(req->i915) >= 6)
 		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
 	/* Optimistic spin for the next ~jiffie before touching IRQs */
@@ -713,7 +713,8 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 			*timeout = 0;
 	}
 
-	if (rps && req->fence.seqno == req->engine->last_submitted_seqno) {
+	if (IS_RPS_USER(rps) &&
+	    req->fence.seqno == req->engine->last_submitted_seqno) {
 		/* The GPU is now idle and this client has stalled.
 		 * Since no other client has submitted a request in the
 		 * meantime, assume that this client is the only one

drivers/gpu/drm/i915/i915_gem_request.h

@@ -206,6 +206,9 @@ void __i915_add_request(struct drm_i915_gem_request *req,
 	__i915_add_request(req, NULL, false)
 
 struct intel_rps_client;
+#define NO_WAITBOOST ERR_PTR(-1)
+#define IS_RPS_CLIENT(p) (!IS_ERR(p))
+#define IS_RPS_USER(p) (!IS_ERR_OR_NULL(p))
 
 int __i915_wait_request(struct drm_i915_gem_request *req,
 			bool interruptible,