drm/i915: Introduce context->enter() and context->exit()

We wish to start segregating the power management into different control
domains, both with respect to the hardware and the user interface. The
first step is that at the lowest level flow of requests, we want to
process a context event (and not a global GEM operation). In this patch,
we introduce the context callbacks that in future patches will be
redirected to per-engine interfaces leading to global operations as
required.

The intent is that this will be guarded by the timeline->mutex, except
that retiring has not quite finished transitioning over from being
guarded by struct_mutex. So at the moment it is protected by
struct_mutex with a reminded to switch.

v2: Rename default handlers to intel_context_enter_engine.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190424200717.1686-3-chris@chris-wilson.co.uk

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

@@ -266,3 +266,20 @@ int __init i915_global_context_init(void)
 	i915_global_register(&global.base);
 	return 0;
 }
+
+void intel_context_enter_engine(struct intel_context *ce)
+{
+	struct drm_i915_private *i915 = ce->gem_context->i915;
+
+	if (!i915->gt.active_requests++)
+		i915_gem_unpark(i915);
+}
+
+void intel_context_exit_engine(struct intel_context *ce)
+{
+	struct drm_i915_private *i915 = ce->gem_context->i915;
+
+	GEM_BUG_ON(!i915->gt.active_requests);
+	if (!--i915->gt.active_requests)
+		i915_gem_park(i915);
+}

drivers/gpu/drm/i915/gt/intel_context.h

@@ -73,6 +73,27 @@ static inline void __intel_context_pin(struct intel_context *ce)
 
 void intel_context_unpin(struct intel_context *ce);
 
+void intel_context_enter_engine(struct intel_context *ce);
+void intel_context_exit_engine(struct intel_context *ce);
+
+static inline void intel_context_enter(struct intel_context *ce)
+{
+	if (!ce->active_count++)
+		ce->ops->enter(ce);
+}
+
+static inline void intel_context_mark_active(struct intel_context *ce)
+{
+	++ce->active_count;
+}
+
+static inline void intel_context_exit(struct intel_context *ce)
+{
+	GEM_BUG_ON(!ce->active_count);
+	if (!--ce->active_count)
+		ce->ops->exit(ce);
+}
+
 static inline struct intel_context *intel_context_get(struct intel_context *ce)
 {
 	kref_get(&ce->ref);

drivers/gpu/drm/i915/gt/intel_context_types.h

@@ -25,6 +25,9 @@ struct intel_context_ops {
 	int (*pin)(struct intel_context *ce);
 	void (*unpin)(struct intel_context *ce);
 
+	void (*enter)(struct intel_context *ce);
+	void (*exit)(struct intel_context *ce);
+
 	void (*reset)(struct intel_context *ce);
 	void (*destroy)(struct kref *kref);
 };
@@ -46,6 +49,8 @@ struct intel_context {
 	u32 *lrc_reg_state;
 	u64 lrc_desc;
 
+	unsigned int active_count; /* notionally protected by timeline->mutex */
+
 	atomic_t pin_count;
 	struct mutex pin_mutex; /* guards pinning and associated on-gpuing */
 

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

@@ -1315,6 +1315,9 @@ static const struct intel_context_ops execlists_context_ops = {
 	.pin = execlists_context_pin,
 	.unpin = execlists_context_unpin,
 
+	.enter = intel_context_enter_engine,
+	.exit = intel_context_exit_engine,
+
 	.reset = execlists_context_reset,
 	.destroy = execlists_context_destroy,
 };

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

@@ -1510,6 +1510,9 @@ static const struct intel_context_ops ring_context_ops = {
 	.pin = ring_context_pin,
 	.unpin = ring_context_unpin,
 
+	.enter = intel_context_enter_engine,
+	.exit = intel_context_exit_engine,
+
 	.reset = ring_context_reset,
 	.destroy = ring_context_destroy,
 };

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

@@ -157,6 +157,9 @@ static const struct intel_context_ops mock_context_ops = {
 	.pin = mock_context_pin,
 	.unpin = mock_context_unpin,
 
+	.enter = intel_context_enter_engine,
+	.exit = intel_context_exit_engine,
+
 	.destroy = mock_context_destroy,
 };
 

drivers/gpu/drm/i915/i915_request.c

@@ -131,19 +131,6 @@ i915_request_remove_from_client(struct i915_request *request)
 	spin_unlock(&file_priv->mm.lock);
 }
 
-static void reserve_gt(struct drm_i915_private *i915)
-{
-	if (!i915->gt.active_requests++)
-		i915_gem_unpark(i915);
-}
-
-static void unreserve_gt(struct drm_i915_private *i915)
-{
-	GEM_BUG_ON(!i915->gt.active_requests);
-	if (!--i915->gt.active_requests)
-		i915_gem_park(i915);
-}
-
 static void advance_ring(struct i915_request *request)
 {
 	struct intel_ring *ring = request->ring;
@@ -301,11 +288,10 @@ static void i915_request_retire(struct i915_request *request)
 
 	i915_request_remove_from_client(request);
 
-	intel_context_unpin(request->hw_context);
-
 	__retire_engine_upto(request->engine, request);
 
-	unreserve_gt(request->i915);
+	intel_context_exit(request->hw_context);
+	intel_context_unpin(request->hw_context);
 
 	i915_sched_node_fini(&request->sched);
 	i915_request_put(request);
@@ -659,8 +645,8 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
 	if (IS_ERR(ce))
 		return ERR_CAST(ce);
 
-	reserve_gt(i915);
 	mutex_lock(&ce->ring->timeline->mutex);
+	intel_context_enter(ce);
 
 	/* Move our oldest request to the slab-cache (if not in use!) */
 	rq = list_first_entry(&ce->ring->request_list, typeof(*rq), ring_link);
@@ -791,8 +777,8 @@ i915_request_alloc(struct intel_engine_cs *engine, struct i915_gem_context *ctx)
 err_free:
 	kmem_cache_free(global.slab_requests, rq);
 err_unreserve:
+	intel_context_exit(ce);
 	mutex_unlock(&ce->ring->timeline->mutex);
-	unreserve_gt(i915);
 	intel_context_unpin(ce);
 	return ERR_PTR(ret);
 }