drm/i915: Fix up the inverse mapping for default ctx->engines[]

The order in which we store the engines inside default_engines() for the
legacy ctx->engines[] has to match the legacy I915_EXEC_RING selector
mapping in execbuf::user_map. If we present VCS2 as being the second
instance of the video engine, legacy userspace calls that I915_EXEC_BSD2
and so we need to insert it into the second video slot.

v2: Record the legacy mapping (hopefully we can remove this need in the
future)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111328
Fixes: 2edda80d ("drm/i915: Rename engines to match their user interface")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com> #v1
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190808110612.23539-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -159,7 +159,7 @@ lookup_user_engine(struct i915_gem_context *ctx,
 		if (!engine)
 			return ERR_PTR(-EINVAL);
 
-		idx = engine->id;
+		idx = engine->legacy_idx;
 	} else {
 		idx = ci->engine_instance;
 	}
@@ -279,6 +279,7 @@ static void free_engines_rcu(struct rcu_head *rcu)
 
 static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
 {
+	const struct intel_gt *gt = &ctx->i915->gt;
 	struct intel_engine_cs *engine;
 	struct i915_gem_engines *e;
 	enum intel_engine_id id;
@@ -288,7 +289,7 @@ static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
 		return ERR_PTR(-ENOMEM);
 
 	init_rcu_head(&e->rcu);
-	for_each_engine(engine, ctx->i915, id) {
+	for_each_engine(engine, gt, id) {
 		struct intel_context *ce;
 
 		ce = intel_context_create(ctx, engine);
@@ -298,8 +299,8 @@ static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
 		}
 
 		e->engines[id] = ce;
+		e->num_engines = id + 1;
 	}
-	e->num_engines = id;
 
 	return e;
 }

drivers/gpu/drm/i915/gem/selftests/igt_gem_utils.c

@@ -23,7 +23,7 @@ igt_request_alloc(struct i915_gem_context *ctx, struct intel_engine_cs *engine)
 	 * GGTT space, so do this first before we reserve a seqno for
 	 * ourselves.
 	 */
-	ce = i915_gem_context_get_engine(ctx, engine->id);
+	ce = i915_gem_context_get_engine(ctx, engine->legacy_idx);
 	if (IS_ERR(ce))
 		return ERR_CAST(ce);
 

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

@@ -264,8 +264,11 @@ struct intel_engine_cs {
 	char name[INTEL_ENGINE_CS_MAX_NAME];
 
 	enum intel_engine_id id;
+	enum intel_engine_id legacy_idx;
+
 	unsigned int hw_id;
 	unsigned int guc_id;
+
 	intel_engine_mask_t mask;
 
 	u8 class;

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

@@ -142,8 +142,57 @@ const char *intel_engine_class_repr(u8 class)
 	return uabi_names[class];
 }
 
+struct legacy_ring {
+	struct intel_gt *gt;
+	u8 class;
+	u8 instance;
+};
+
+static int legacy_ring_idx(const struct legacy_ring *ring)
+{
+	static const struct {
+		u8 base, max;
+	} map[] = {
+		[RENDER_CLASS] = { RCS0, 1 },
+		[COPY_ENGINE_CLASS] = { BCS0, 1 },
+		[VIDEO_DECODE_CLASS] = { VCS0, I915_MAX_VCS },
+		[VIDEO_ENHANCEMENT_CLASS] = { VECS0, I915_MAX_VECS },
+	};
+
+	if (GEM_DEBUG_WARN_ON(ring->class >= ARRAY_SIZE(map)))
+		return -1;
+
+	if (GEM_DEBUG_WARN_ON(ring->instance >= map[ring->class].max))
+		return -1;
+
+	return map[ring->class].base + ring->instance;
+}
+
+static void add_legacy_ring(struct legacy_ring *ring,
+			    struct intel_engine_cs *engine)
+{
+	int idx;
+
+	if (engine->gt != ring->gt || engine->class != ring->class) {
+		ring->gt = engine->gt;
+		ring->class = engine->class;
+		ring->instance = 0;
+	}
+
+	idx = legacy_ring_idx(ring);
+	if (unlikely(idx == -1))
+		return;
+
+	GEM_BUG_ON(idx >= ARRAY_SIZE(ring->gt->engine));
+	ring->gt->engine[idx] = engine;
+	ring->instance++;
+
+	engine->legacy_idx = idx;
+}
+
 void intel_engines_driver_register(struct drm_i915_private *i915)
 {
+	struct legacy_ring ring = {};
 	u8 uabi_instances[4] = {};
 	struct list_head *it, *next;
 	struct rb_node **p, *prev;
@@ -179,6 +228,9 @@ void intel_engines_driver_register(struct drm_i915_private *i915)
 						    engine->uabi_class,
 						    engine->uabi_instance) != engine);
 
+		/* Fix up the mapping to match default execbuf::user_map[] */
+		add_legacy_ring(&ring, engine);
+
 		prev = &engine->uabi_node;
 		p = &prev->rb_right;
 	}

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

@@ -78,6 +78,7 @@ struct intel_gt {
 
 	u32 pm_guc_events;
 
+	struct intel_engine_cs *engine[I915_NUM_ENGINES];
 	struct intel_engine_cs *engine_class[MAX_ENGINE_CLASS + 1]
 					    [MAX_ENGINE_INSTANCE + 1];
 };

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

@@ -490,7 +490,7 @@ spinner_create_request(struct igt_spinner *spin,
 	struct intel_context *ce;
 	struct i915_request *rq;
 
-	ce = i915_gem_context_get_engine(ctx, engine->id);
+	ce = i915_gem_context_get_engine(ctx, engine->legacy_idx);
 	if (IS_ERR(ce))
 		return ERR_CAST(ce);
 

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

@@ -250,7 +250,7 @@ switch_to_scratch_context(struct intel_engine_cs *engine,
 
 	GEM_BUG_ON(i915_gem_context_is_bannable(ctx));
 
-	ce = i915_gem_context_get_engine(ctx, engine->id);
+	ce = i915_gem_context_get_engine(ctx, engine->legacy_idx);
 	GEM_BUG_ON(IS_ERR(ce));
 
 	rq = ERR_PTR(-ENODEV);