drm/i915: abolish separate per-ring default_context pointers

Now that we've eliminated a lot of uses of ring->default_context,
we can eliminate the pointer itself.

All the engines share the same default intel_context, so we can just
keep a single reference to it in the dev_priv structure rather than one
in each of the engine[] elements. This make refcounting more sensible
too, as we now have a refcount of one for the one pointer, rather than
a refcount of one but multiple pointers.

From an idea by Chris Wilson.

v2:	transform an extra instance of ring->default_context introduced by
    42f1cae8c drm/i915: Restore inhibiting the load of the default context
    That patch's commentary includes:
	v2: Mark the global default context as uninitialized on GPU reset so
	    that the context-local workarounds are reloaded upon re-enabling
    The code implementing that now also benefits from the replacement of
    the multiple (per-ring) pointers to the default context with a single
    pointer to the unique kernel context.

v4:	Rebased, remove underused local (Nick Hoath)

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Nick Hoath <nicholas.hoath@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1453230175-19330-3-git-send-email-david.s.gordon@intel.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1961,7 +1961,7 @@ static int i915_context_status(struct seq_file *m, void *unused)
 		seq_puts(m, "HW context ");
 		describe_ctx(m, ctx);
 		for_each_ring(ring, dev_priv, i) {
-			if (ring->default_context == ctx)
+			if (dev_priv->kernel_context == ctx)
 				seq_printf(m, "(default context %s) ",
 					   ring->name);
 		}
@@ -2058,7 +2058,7 @@ static int i915_dump_lrc(struct seq_file *m, void *unused)
 
 	list_for_each_entry(ctx, &dev_priv->context_list, link) {
 		for_each_ring(ring, dev_priv, i) {
-			if (ring->default_context != ctx)
+			if (dev_priv->kernel_context != ctx)
 				i915_dump_lrc_obj(m, ctx, ring);
 		}
 	}

drivers/gpu/drm/i915/i915_drv.h

@@ -1948,6 +1948,8 @@ struct drm_i915_private {
 		void (*stop_ring)(struct intel_engine_cs *ring);
 	} gt;
 
+	struct intel_context *kernel_context;
+
 	bool edp_low_vswing;
 
 	/* perform PHY state sanity checks? */

drivers/gpu/drm/i915/i915_gem.c

@@ -2680,7 +2680,7 @@ void i915_gem_request_free(struct kref *req_ref)
 
 	if (ctx) {
 		if (i915.enable_execlists) {
-			if (ctx != req->ring->default_context)
+			if (ctx != req->i915->kernel_context)
 				intel_lr_context_unpin(req);
 		}
 
@@ -2776,7 +2776,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 	int err;
 
 	if (ctx == NULL)
-		ctx = engine->default_context;
+		ctx = to_i915(engine->dev)->kernel_context;
 	err = __i915_gem_request_alloc(engine, ctx, &req);
 	return err ? ERR_PTR(err) : req;
 }
@@ -4864,7 +4864,7 @@ i915_gem_init_hw(struct drm_device *dev)
 	 */
 	init_unused_rings(dev);
 
-	BUG_ON(!dev_priv->ring[RCS].default_context);
+	BUG_ON(!dev_priv->kernel_context);
 
 	ret = i915_ppgtt_init_hw(dev);
 	if (ret) {

drivers/gpu/drm/i915/i915_gem_context.c

@@ -347,22 +347,20 @@ void i915_gem_context_reset(struct drm_device *dev)
 			i915_gem_context_unreference(lctx);
 			ring->last_context = NULL;
 		}
-
-		/* Force the GPU state to be reinitialised on enabling */
-		if (ring->default_context)
-			ring->default_context->legacy_hw_ctx.initialized = false;
 	}
+
+	/* Force the GPU state to be reinitialised on enabling */
+	dev_priv->kernel_context->legacy_hw_ctx.initialized = false;
 }
 
 int i915_gem_context_init(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_context *ctx;
-	int i;
 
 	/* Init should only be called once per module load. Eventually the
 	 * restriction on the context_disabled check can be loosened. */
-	if (WARN_ON(dev_priv->ring[RCS].default_context))
+	if (WARN_ON(dev_priv->kernel_context))
 		return 0;
 
 	if (intel_vgpu_active(dev) && HAS_LOGICAL_RING_CONTEXTS(dev)) {
@@ -392,12 +390,7 @@ int i915_gem_context_init(struct drm_device *dev)
 		return PTR_ERR(ctx);
 	}
 
-	for (i = 0; i < I915_NUM_RINGS; i++) {
-		struct intel_engine_cs *ring = &dev_priv->ring[i];
-
-		/* NB: RCS will hold a ref for all rings */
-		ring->default_context = ctx;
-	}
+	dev_priv->kernel_context = ctx;
 
 	DRM_DEBUG_DRIVER("%s context support initialized\n",
 			i915.enable_execlists ? "LR" :
@@ -408,7 +401,7 @@ int i915_gem_context_init(struct drm_device *dev)
 void i915_gem_context_fini(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_context *dctx = dev_priv->ring[RCS].default_context;
+	struct intel_context *dctx = dev_priv->kernel_context;
 	int i;
 
 	if (dctx->legacy_hw_ctx.rcs_state) {
@@ -435,17 +428,17 @@ void i915_gem_context_fini(struct drm_device *dev)
 		i915_gem_object_ggtt_unpin(dctx->legacy_hw_ctx.rcs_state);
 	}
 
-	for (i = 0; i < I915_NUM_RINGS; i++) {
+	for (i = I915_NUM_RINGS; --i >= 0;) {
 		struct intel_engine_cs *ring = &dev_priv->ring[i];
 
-		if (ring->last_context)
+		if (ring->last_context) {
 			i915_gem_context_unreference(ring->last_context);
-
-		ring->default_context = NULL;
-		ring->last_context = NULL;
+			ring->last_context = NULL;
+		}
 	}
 
 	i915_gem_context_unreference(dctx);
+	dev_priv->kernel_context = NULL;
 }
 
 int i915_gem_context_enable(struct drm_i915_gem_request *req)

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -1050,7 +1050,7 @@ static void i915_gem_record_rings(struct drm_device *dev,
 			if (request)
 				rbuf = request->ctx->engine[ring->id].ringbuf;
 			else
-				rbuf = ring->default_context->engine[ring->id].ringbuf;
+				rbuf = dev_priv->kernel_context->engine[ring->id].ringbuf;
 		} else
 			rbuf = ring->buffer;
 

drivers/gpu/drm/i915/i915_guc_submission.c

@@ -964,7 +964,7 @@ int i915_guc_submission_enable(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_guc *guc = &dev_priv->guc;
-	struct intel_context *ctx = dev_priv->ring[RCS].default_context;
+	struct intel_context *ctx = dev_priv->kernel_context;
 	struct i915_guc_client *client;
 
 	/* client for execbuf submission */
@@ -1021,7 +1021,7 @@ int intel_guc_suspend(struct drm_device *dev)
 	if (!i915.enable_guc_submission)
 		return 0;
 
-	ctx = dev_priv->ring[RCS].default_context;
+	ctx = dev_priv->kernel_context;
 
 	data[0] = HOST2GUC_ACTION_ENTER_S_STATE;
 	/* any value greater than GUC_POWER_D0 */
@@ -1047,7 +1047,7 @@ int intel_guc_resume(struct drm_device *dev)
 	if (!i915.enable_guc_submission)
 		return 0;
 
-	ctx = dev_priv->ring[RCS].default_context;
+	ctx = dev_priv->kernel_context;
 
 	data[0] = HOST2GUC_ACTION_EXIT_S_STATE;
 	data[1] = GUC_POWER_D0;

drivers/gpu/drm/i915/intel_lrc.c

@@ -598,7 +598,7 @@ static int execlists_context_queue(struct drm_i915_gem_request *request)
 	struct drm_i915_gem_request *cursor;
 	int num_elements = 0;
 
-	if (request->ctx != ring->default_context)
+	if (request->ctx != request->i915->kernel_context)
 		intel_lr_context_pin(request);
 
 	i915_gem_request_reference(request);
@@ -690,7 +690,7 @@ int intel_logical_ring_alloc_request_extras(struct drm_i915_gem_request *request
 
 	request->ringbuf = request->ctx->engine[request->ring->id].ringbuf;
 
-	if (request->ctx != request->ring->default_context) {
+	if (request->ctx != request->i915->kernel_context) {
 		ret = intel_lr_context_pin(request);
 		if (ret)
 			return ret;
@@ -1006,7 +1006,7 @@ void intel_execlists_retire_requests(struct intel_engine_cs *ring)
 		struct drm_i915_gem_object *ctx_obj =
 				ctx->engine[ring->id].state;
 
-		if (ctx_obj && (ctx != ring->default_context))
+		if (ctx_obj && (ctx != req->i915->kernel_context))
 			intel_lr_context_unpin(req);
 		list_del(&req->execlist_link);
 		i915_gem_request_unreference(req);
@@ -1529,7 +1529,7 @@ static int gen8_init_common_ring(struct intel_engine_cs *ring)
 	u8 next_context_status_buffer_hw;
 
 	lrc_setup_hardware_status_page(ring,
-				ring->default_context->engine[ring->id].state);
+				dev_priv->kernel_context->engine[ring->id].state);
 
 	I915_WRITE_IMR(ring, ~(ring->irq_enable_mask | ring->irq_keep_mask));
 	I915_WRITE(RING_HWSTAM(ring->mmio_base), 0xffffffff);
@@ -2005,6 +2005,7 @@ logical_ring_default_irqs(struct intel_engine_cs *ring, unsigned shift)
 static int
 logical_ring_init(struct drm_device *dev, struct intel_engine_cs *ring)
 {
+	struct intel_context *dctx = to_i915(dev)->kernel_context;
 	int ret;
 
 	/* Intentionally left blank. */
@@ -2027,12 +2028,12 @@ logical_ring_init(struct drm_device *dev, struct intel_engine_cs *ring)
 	if (ret)
 		goto error;
 
-	ret = intel_lr_context_deferred_alloc(ring->default_context, ring);
+	ret = intel_lr_context_deferred_alloc(dctx, ring);
 	if (ret)
 		goto error;
 
 	/* As this is the default context, always pin it */
-	ret = intel_lr_context_do_pin(ring, ring->default_context);
+	ret = intel_lr_context_do_pin(ring, dctx);
 	if (ret) {
 		DRM_ERROR(
 			"Failed to pin and map ringbuffer %s: %d\n",
@@ -2398,7 +2399,7 @@ void intel_lr_context_free(struct intel_context *ctx)
 					ctx->engine[i].ringbuf;
 			struct intel_engine_cs *ring = ringbuf->ring;
 
-			if (ctx == ring->default_context) {
+			if (ctx == ctx->i915->kernel_context) {
 				intel_unpin_ringbuffer_obj(ringbuf);
 				i915_gem_object_ggtt_unpin(ctx_obj);
 			}
@@ -2517,7 +2518,7 @@ int intel_lr_context_deferred_alloc(struct intel_context *ctx,
 	ctx->engine[ring->id].ringbuf = ringbuf;
 	ctx->engine[ring->id].state = ctx_obj;
 
-	if (ctx != ring->default_context && ring->init_context) {
+	if (ctx != ctx->i915->kernel_context && ring->init_context) {
 		struct drm_i915_gem_request *req;
 
 		req = i915_gem_request_alloc(ring, ctx);

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -309,7 +309,6 @@ struct  intel_engine_cs {
 
 	wait_queue_head_t irq_queue;
 
-	struct intel_context *default_context;
 	struct intel_context *last_context;
 
 	struct intel_ring_hangcheck hangcheck;