drm/i915: Treat kernel context as initialised

The kernel context exists simply as a placeholder and should never be
executed with a render context. It does not need the golden render
state, as that will always be applied to a user context. By skipping the
initialisation we can avoid issues in attempting to program the golden
render context when trying to make the hardware idle.

v2: Rebase

Testcase: igt/drm_module_reload_basic #byt
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95634
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466776558-21516-3-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -472,13 +472,17 @@ void i915_gem_context_lost(struct drm_i915_private *dev_priv)
 			i915_gem_context_unpin(engine->last_context, engine);
 			engine->last_context = NULL;
 		}
-
-		/* Force the GPU state to be reinitialised on enabling */
-		dev_priv->kernel_context->engine[engine->id].initialised =
-			engine->init_context == NULL;
 	}
 
-	/* Force the GPU state to be reinitialised on enabling */
+	/* Force the GPU state to be restored on enabling */
+	if (!i915.enable_execlists) {
+		for_each_engine(engine, dev_priv) {
+			struct intel_context *kce =
+				&dev_priv->kernel_context->engine[engine->id];
+
+			kce->initialised = true;
+		}
+	}
 	dev_priv->kernel_context->remap_slice = ALL_L3_SLICES(dev_priv);
 }
 

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -2338,6 +2338,16 @@ static int intel_ring_context_pin(struct i915_gem_context *ctx,
 			goto error;
 	}
 
+	/* The kernel context is only used as a placeholder for flushing the
+	 * active context. It is never used for submitting user rendering and
+	 * as such never requires the golden render context, and so we can skip
+	 * emitting it when we switch to the kernel context. This is required
+	 * as during eviction we cannot allocate and pin the renderstate in
+	 * order to initialise the context.
+	 */
+	if (ctx == ctx->i915->kernel_context)
+		ce->initialised = true;
+
 	i915_gem_context_reference(ctx);
 	return 0;