[PATCH v2 3/6] drm/i915: Treat kernel context as initialised

[Chris Wilson <chris@chris-wilson.co.uk>]

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.

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>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 13 ++++++++-----
 drivers/gpu/drm/i915/intel_ringbuffer.c |  9 ++++++++-
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index c620fe6c9d96..46cb2c7fd158 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -434,13 +434,16 @@ 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 */
+	for_each_engine(engine, dev_priv) {
+		struct intel_context *ce =
+			&dev_priv->kernel_context->engine[engine->id];
+
+		ce->initialised =
+			!i915.enable_execlists || engine->init_context == NULL;
+	}
 	dev_priv->kernel_context->remap_slice = ALL_L3_SLICES(dev_priv);
 }
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 4e0aa7e9d5da..203b7952052a 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2278,7 +2278,14 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 		if (ret)
 			goto error;
 
-		ce->initialised = false;
+		/* The kernel context is only used as a placeholder
+		 * for flushing the active context. It is never used
+		 * for submitting rendering and as such never requires
+		 * the golden render context, and so we can skip
+		 * emitting it when we switch to the kernel context
+		 * (during eviction).
+		 */
+		ce->initialised = true;
 	}
 
 	ringbuf = intel_engine_create_ringbuffer(engine, 32 * PAGE_SIZE);
-- 
2.8.1

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