drm/i915/gt: Mark up the nested engine-pm timeline lock as irqsafe

We use a fake timeline->mutex lock to reassure lockdep that the timeline
is always locked when emitting requests. However, the use inside
__engine_park() may be inside hardirq and so lockdep now complains about
the mixed irq-state of the nested locked. Disable irqs around the
lockdep tracking to keep it happy.

Fixes: 6c69a45 ("drm/i915/gt: Mark context->active_count as protected by timeline->mutex")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190819075835.20065-3-chris@chris-wilson.co.uk

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

@@ -37,16 +37,34 @@ static int __engine_unpark(struct intel_wakeref *wf)
 	return 0;
 }
 
+#if IS_ENABLED(CONFIG_LOCKDEP)
+
 static inline void __timeline_mark_lock(struct intel_context *ce)
 {
+	unsigned long flags;
+
+	local_irq_save(flags);
 	mutex_acquire(&ce->timeline->mutex.dep_map, 2, 0, _THIS_IP_);
+	local_irq_restore(flags);
 }
 
 static inline void __timeline_mark_unlock(struct intel_context *ce)
 {
 	mutex_release(&ce->timeline->mutex.dep_map, 0, _THIS_IP_);
 }
 
+#else
+
+static inline void __timeline_mark_lock(struct intel_context *ce)
+{
+}
+
+static inline void __timeline_mark_unlock(struct intel_context *ce)
+{
+}
+
+#endif /* !IS_ENABLED(CONFIG_LOCKDEP) */
+
 static bool switch_to_kernel_context(struct intel_engine_cs *engine)
 {
 	struct i915_request *rq;