drm/i915: Add per context timelines to fence object

The fence object used inside the request structure requires a sequence
number. Although this is not used by the i915 driver itself, it could
potentially be used by non-i915 code if the fence is passed outside of
the driver. This is the intention as it allows external kernel drivers
and user applications to wait on batch buffer completion
asynchronously via the dma-buff fence API.

To ensure that such external users are not confused by strange things
happening with the seqno, this patch adds in a per context timeline
that can provide a guaranteed in-order seqno value for the fence. This
is safe because the scheduler will not re-order batch buffers within a
context - they are considered to be mutually dependent.

v2: New patch in series.

v3: Renamed/retyped timeline structure fields after review comments by
Tvrtko Ursulin.

Added context information to the timeline's name string for better
identification in debugfs output.

v5: Line wrapping and other white space fixes to keep style checker
happy.

v7: Updated to newer nightly (lots of ring -> engine renaming).

For: VIZ-5190
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

5 files changed, 114 insertions, 17 deletions

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index bb18b8997319..1c3a1caf4f40 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -813,6 +813,15 @@ struct i915_ctx_hang_stats {
 	bool banned;
 };
 
+struct i915_fence_timeline {
+	char        name[32];
+	unsigned    fence_context;
+	unsigned    next;
+
+	struct intel_context *ctx;
+	struct intel_engine_cs *engine;
+};
+
 /* This must match up with the value previously used for execbuf2.rsvd1. */
 #define DEFAULT_CONTEXT_HANDLE 0
 
@@ -860,6 +869,7 @@ struct intel_context {
 		struct i915_vma *lrc_vma;
 		u64 lrc_desc;
 		uint32_t *lrc_reg_state;
+		struct i915_fence_timeline fence_timeline;
 	} engine[I915_NUM_ENGINES];
 
 	struct list_head link;
@@ -2245,13 +2255,10 @@ void i915_gem_track_fb(struct drm_i915_gem_object *old,
 struct drm_i915_gem_request {
 	/**
 	 * Underlying object for implementing the signal/wait stuff.
-	 * NB: Never call fence_later() or return this fence object to user
-	 * land! Due to lazy allocation, scheduler re-ordering, pre-emption,
-	 * etc., there is no guarantee at all about the validity or
-	 * sequentiality of the fence's seqno! It is also unsafe to let
-	 * anything outside of the i915 driver get hold of the fence object
-	 * as the clean up when decrementing the reference count requires
-	 * holding the driver mutex lock.
+	 * NB: Never return this fence object to user land! It is unsafe to
+	 * let anything outside of the i915 driver get hold of the fence
+	 * object as the clean up when decrementing the reference count
+	 * requires holding the driver mutex lock.
 	 */
 	struct fence fence;
 
@@ -2340,6 +2347,10 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
 		       struct intel_context *ctx);
 void i915_gem_request_cancel(struct drm_i915_gem_request *req);
 
+int i915_create_fence_timeline(struct drm_device *dev,
+			       struct intel_context *ctx,
+			       struct intel_engine_cs *ring);
+
 static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
 {
 	return fence_is_signaled(&req->fence);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d20c58104f06..5f4bc4e41312 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2776,9 +2776,35 @@ static const char *i915_gem_request_get_driver_name(struct fence *req_fence)
 
 static const char *i915_gem_request_get_timeline_name(struct fence *req_fence)
 {
-	struct drm_i915_gem_request *req = container_of(req_fence,
-						 typeof(*req), fence);
-	return req->engine->name;
+	struct drm_i915_gem_request *req;
+	struct i915_fence_timeline *timeline;
+
+	req = container_of(req_fence, typeof(*req), fence);
+	timeline = &req->ctx->engine[req->engine->id].fence_timeline;
+
+	return timeline->name;
+}
+
+static void i915_gem_request_timeline_value_str(struct fence *req_fence,
+						char *str, int size)
+{
+	struct drm_i915_gem_request *req;
+
+	req = container_of(req_fence, typeof(*req), fence);
+
+	/* Last signalled timeline value ??? */
+	snprintf(str, size, "? [%d]"/*, timeline->value*/,
+		 req->engine->get_seqno(req->engine));
+}
+
+static void i915_gem_request_fence_value_str(struct fence *req_fence,
+					     char *str, int size)
+{
+	struct drm_i915_gem_request *req;
+
+	req = container_of(req_fence, typeof(*req), fence);
+
+	snprintf(str, size, "%d [%d]", req->fence.seqno, req->seqno);
 }
 
 static const struct fence_ops i915_gem_request_fops = {
@@ -2788,8 +2814,50 @@ static const struct fence_ops i915_gem_request_fops = {
 	.release		= i915_gem_request_free,
 	.get_driver_name	= i915_gem_request_get_driver_name,
 	.get_timeline_name	= i915_gem_request_get_timeline_name,
+	.fence_value_str	= i915_gem_request_fence_value_str,
+	.timeline_value_str	= i915_gem_request_timeline_value_str,
 };
 
+int i915_create_fence_timeline(struct drm_device *dev,
+			       struct intel_context *ctx,
+			       struct intel_engine_cs *engine)
+{
+	struct i915_fence_timeline *timeline;
+
+	timeline = &ctx->engine[engine->id].fence_timeline;
+
+	if (timeline->engine)
+		return 0;
+
+	timeline->fence_context = fence_context_alloc(1);
+
+	/*
+	 * Start the timeline from seqno 0 as this is a special value
+	 * that is reserved for invalid sync points.
+	 */
+	timeline->next       = 1;
+	timeline->ctx        = ctx;
+	timeline->engine     = engine;
+
+	snprintf(timeline->name, sizeof(timeline->name), "%d>%s:%d",
+		 timeline->fence_context, engine->name, ctx->user_handle);
+
+	return 0;
+}
+
+static unsigned i915_fence_timeline_get_next_seqno(struct i915_fence_timeline *timeline)
+{
+	unsigned seqno;
+
+	seqno = timeline->next;
+
+	/* Reserve zero for invalid */
+	if (++timeline->next == 0)
+		timeline->next = 1;
+
+	return seqno;
+}
+
 static inline int
 __i915_gem_request_alloc(struct intel_engine_cs *engine,
 			 struct intel_context *ctx,
@@ -2827,7 +2895,8 @@ __i915_gem_request_alloc(struct intel_engine_cs *engine,
 	}
 
 	fence_init(&req->fence, &i915_gem_request_fops, &engine->fence_lock,
-		   engine->fence_context, req->seqno);
+		   ctx->engine[engine->id].fence_timeline.fence_context,
+		   i915_fence_timeline_get_next_seqno(&ctx->engine[engine->id].fence_timeline));
 
 	/*
 	 * Reserve space in the ring buffer for all the commands required to
@@ -4936,7 +5005,7 @@ i915_gem_init_hw(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_engine_cs *engine;
-	int ret, j, fence_base;
+	int ret, j;
 
 	if (INTEL_INFO(dev)->gen < 6 && !intel_enable_gtt())
 		return -EIO;
@@ -5006,14 +5075,10 @@ i915_gem_init_hw(struct drm_device *dev)
 	if (ret)
 		goto out;
 
-	fence_base = fence_context_alloc(I915_NUM_ENGINES);
-
 	/* Now it is safe to go back round and do everything else: */
 	for_each_engine(engine, dev_priv) {
 		struct drm_i915_gem_request *req;
 
-		engine->fence_context = fence_base + engine->id;
-
 		req = i915_gem_request_alloc(engine, NULL);
 		if (IS_ERR(req)) {
 			ret = PTR_ERR(req);
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 91028d9c6269..05d8f43f3533 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -279,6 +279,20 @@ i915_gem_create_context(struct drm_device *dev,
 	if (IS_ERR(ctx))
 		return ctx;
 
+	if (!i915.enable_execlists) {
+		struct intel_engine_cs *engine;
+
+		/* Create a per context timeline for fences */
+		for_each_engine(engine, to_i915(dev)) {
+			ret = i915_create_fence_timeline(dev, ctx, engine);
+			if (ret) {
+				DRM_ERROR("Fence timeline creation failed for legacy %s: %p\n",
+					  engine->name, ctx);
+				goto err_destroy;
+			}
+		}
+	}
+
 	if (is_global_default_ctx && ctx->legacy_hw_ctx.rcs_state) {
 		/* We may need to do things with the shrinker which
 		 * require us to immediately switch back to the default
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 268e024aa5a4..db74cc142f44 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -2694,6 +2694,14 @@ int intel_lr_context_deferred_alloc(struct intel_context *ctx,
 		goto error_ringbuf;
 	}
 
+	/* Create a per context timeline for fences */
+	ret = i915_create_fence_timeline(dev, ctx, engine);
+	if (ret) {
+		DRM_ERROR("Fence timeline creation failed for engine %s, ctx %p\n",
+			  engine->name, ctx);
+		goto error_ringbuf;
+	}
+
 	ctx->engine[engine->id].ringbuf = ringbuf;
 	ctx->engine[engine->id].state = ctx_obj;
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 2cd9d2c0bc0d..23e1d94d2b38 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -349,7 +349,6 @@ struct  intel_engine_cs {
 	 */
 	u32 (*get_cmd_length_mask)(u32 cmd_header);
 
-	unsigned fence_context;
 	spinlock_t fence_lock;
 };