drm/i915/execlists: Leave tell-tales as to why pending[] is bad

Before we BUG out with bad pending state, leave a telltale as to which
test failed.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010071434.31195-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -1089,25 +1089,45 @@ assert_pending_valid(const struct intel_engine_execlists *execlists,
 
 	trace_ports(execlists, msg, execlists->pending);
 
-	if (!execlists->pending[0])
+	if (!execlists->pending[0]) {
+		GEM_TRACE_ERR("Nothing pending for promotion!\n");
 		return false;
+	}
 
-	if (execlists->pending[execlists_num_ports(execlists)])
+	if (execlists->pending[execlists_num_ports(execlists)]) {
+		GEM_TRACE_ERR("Excess pending[%d] for promotion!\n",
+			      execlists_num_ports(execlists));
 		return false;
+	}
 
 	for (port = execlists->pending; (rq = *port); port++) {
-		if (ce == rq->hw_context)
+		if (ce == rq->hw_context) {
+			GEM_TRACE_ERR("Duplicate context in pending[%zd]\n",
+				      port - execlists->pending);
 			return false;
+		}
 
 		ce = rq->hw_context;
 		if (i915_request_completed(rq))
 			continue;
 
-		if (i915_active_is_idle(&ce->active))
+		if (i915_active_is_idle(&ce->active)) {
+			GEM_TRACE_ERR("Inactive context in pending[%zd]\n",
+				      port - execlists->pending);
+			return false;
+		}
+
+		if (!i915_vma_is_pinned(ce->state)) {
+			GEM_TRACE_ERR("Unpinned context in pending[%zd]\n",
+				      port - execlists->pending);
 			return false;
+		}
 
-		if (!i915_vma_is_pinned(ce->state))
+		if (!i915_vma_is_pinned(ce->ring->vma)) {
+			GEM_TRACE_ERR("Unpinned ringbuffer in pending[%zd]\n",
+				      port - execlists->pending);
 			return false;
+		}
 	}
 
 	return ce;

drivers/gpu/drm/i915/i915_gem.h

@@ -37,10 +37,8 @@ struct drm_i915_private;
 #define GEM_SHOW_DEBUG() (drm_debug & DRM_UT_DRIVER)
 
 #define GEM_BUG_ON(condition) do { if (unlikely((condition))) {	\
-		pr_err("%s:%d GEM_BUG_ON(%s)\n", \
-		       __func__, __LINE__, __stringify(condition)); \
-		GEM_TRACE("%s:%d GEM_BUG_ON(%s)\n", \
-			  __func__, __LINE__, __stringify(condition)); \
+		GEM_TRACE_ERR("%s:%d GEM_BUG_ON(%s)\n", \
+			      __func__, __LINE__, __stringify(condition)); \
 		BUG(); \
 		} \
 	} while(0)
@@ -66,11 +64,16 @@ struct drm_i915_private;
 
 #if IS_ENABLED(CONFIG_DRM_I915_TRACE_GEM)
 #define GEM_TRACE(...) trace_printk(__VA_ARGS__)
+#define GEM_TRACE_ERR(...) do {						\
+	pr_err(__VA_ARGS__);						\
+	trace_printk(__VA_ARGS__);					\
+} while (0)
 #define GEM_TRACE_DUMP() ftrace_dump(DUMP_ALL)
 #define GEM_TRACE_DUMP_ON(expr) \
 	do { if (expr) ftrace_dump(DUMP_ALL); } while (0)
 #else
 #define GEM_TRACE(...) do { } while (0)
+#define GEM_TRACE_ERR(...) do { } while (0)
 #define GEM_TRACE_DUMP() do { } while (0)
 #define GEM_TRACE_DUMP_ON(expr) BUILD_BUG_ON_INVALID(expr)
 #endif