drm/xe: Introduce xe_engine_is_idle()

Introduce xe_engine_is_idle, and replace the static function in
xe_migrate.c.
The latter had two flaws. First the seqno == 1 test might return a false
true value each time the seqno counter wrapped, Second, the
cur_seqno == next_seqno test would never return true.
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_engine.c

@@ -683,6 +683,29 @@ static void engine_kill_compute(struct xe_engine *e)
 	up_write(&e->vm->lock);
 }
 
+/**
+ * xe_engine_is_idle() - Whether an engine is idle.
+ * @engine: The engine
+ *
+ * FIXME: Need to determine what to use as the short-lived
+ * timeline lock for the engines, so that the return value
+ * of this function becomes more than just an advisory
+ * snapshot in time. The timeline lock must protect the
+ * seqno from racing submissions on the same engine.
+ * Typically vm->resv, but user-created timeline locks use the migrate vm
+ * and never grabs the migrate vm->resv so we have a race there.
+ *
+ * Return: True if the engine is idle, false otherwise.
+ */
+bool xe_engine_is_idle(struct xe_engine *engine)
+{
+	if (XE_WARN_ON(xe_engine_is_parallel(engine)))
+		return false;
+
+	return xe_lrc_seqno(&engine->lrc[0]) ==
+		engine->lrc[0].fence_ctx.next_seqno - 1;
+}
+
 void xe_engine_kill(struct xe_engine *e)
 {
 	struct xe_engine *engine = e, *next;

drivers/gpu/drm/xe/xe_engine.h

@@ -42,6 +42,8 @@ static inline bool xe_engine_is_parallel(struct xe_engine *engine)
 	return engine->width > 1;
 }
 
+bool xe_engine_is_idle(struct xe_engine *engine);
+
 void xe_engine_kill(struct xe_engine *e);
 
 int xe_engine_create_ioctl(struct drm_device *dev, void *data,

drivers/gpu/drm/xe/xe_migrate.c

@@ -1024,12 +1024,6 @@ static bool no_in_syncs(struct xe_sync_entry *syncs, u32 num_syncs)
 	return true;
 }
 
-static bool engine_is_idle(struct xe_engine *e)
-{
-	return !e || e->lrc[0].fence_ctx.next_seqno == 1 ||
-		xe_lrc_seqno(&e->lrc[0]) == e->lrc[0].fence_ctx.next_seqno;
-}
-
 /**
  * xe_migrate_update_pgtables() - Pipelined page-table update
  * @m: The migrate context.
@@ -1082,7 +1076,7 @@ xe_migrate_update_pgtables(struct xe_migrate *m,
 	bool first_munmap_rebind = vma && vma->first_munmap_rebind;
 
 	/* Use the CPU if no in syncs and engine is idle */
-	if (no_in_syncs(syncs, num_syncs) && engine_is_idle(eng)) {
+	if (no_in_syncs(syncs, num_syncs) && (!eng || xe_engine_is_idle(eng))) {
 		fence =  xe_migrate_update_pgtables_cpu(m, vm, bo, updates,
 							num_updates,
 							first_munmap_rebind,