[Intel-gfx] [PATCH v8 1/6] drm/i915: Add per context timelines to fence object

[John.C.Harrison at Intel.com]

From: John Harrison <John.C.Harrison at Intel.com>

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).

v8: Moved to earlier in patch series so no longer needs to remove the
quick hack timeline that was being added before.

For: VIZ-5190
Signed-off-by: John Harrison <John.C.Harrison at Intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
---
 drivers/gpu/drm/i915/i915_drv.h         | 14 ++++++++++++
 drivers/gpu/drm/i915/i915_gem.c         | 40 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_context.c | 14 ++++++++++++
 drivers/gpu/drm/i915/intel_lrc.c        |  8 +++++++
 4 files changed, 76 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d5496ab..520480b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -818,6 +818,19 @@ 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;
+};
+
+int i915_create_fence_timeline(struct drm_device *dev,
+			       struct intel_context *ctx,
+			       struct intel_engine_cs *ring);
+
 /* This must match up with the value previously used for execbuf2.rsvd1. */
 #define DEFAULT_CONTEXT_HANDLE 0
 
@@ -869,6 +882,7 @@ struct intel_context {
 		u64 lrc_desc;
 		uint32_t *lrc_reg_state;
 		bool initialised;
+		struct i915_fence_timeline fence_timeline;
 	} engine[I915_NUM_ENGINES];
 
 	struct list_head link;
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c2548bd..99bd470 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2723,6 +2723,46 @@ void i915_gem_request_free(struct kref *req_ref)
 	kmem_cache_free(req->i915->requests, req);
 }
 
+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;
+}
+
+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,
diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index de8d878..e90762e 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -311,6 +311,20 @@ 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 d876352..5e15fbe 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -2526,6 +2526,14 @@ static int execlists_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;
 	ctx->engine[engine->id].initialised = engine->init_context == NULL;
-- 
1.9.1