drm/i915/icl: Ringbuffer interrupt handling

On Gen11 interrupt masks need to be clear to allow C6 entry.
We keep them all enabled knowing that we generate extra
interrupts.

v2: Rebase.
v3: Remove gen 11 extra check in logical_render_ring_init.
v4: Rebase fixes.
v5: Rebase/refactor.
v6: Rebase.
v7: Rebase.
v8: Update comment and commit message (Daniele)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180302161501.28594-1-mika.kuoppala@linux.intel.com
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index a8369064..094f010 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -168,17 +168,21 @@ static void irq_enable(struct intel_engine_cs *engine)
 	set_bit(ENGINE_IRQ_BREADCRUMB, &engine->irq_posted);
 
 	/* Caller disables interrupts */
-	spin_lock(&engine->i915->irq_lock);
-	engine->irq_enable(engine);
-	spin_unlock(&engine->i915->irq_lock);
+	if (engine->irq_enable) {
+		spin_lock(&engine->i915->irq_lock);
+		engine->irq_enable(engine);
+		spin_unlock(&engine->i915->irq_lock);
+	}
 }
 
 static void irq_disable(struct intel_engine_cs *engine)
 {
 	/* Caller disables interrupts */
-	spin_lock(&engine->i915->irq_lock);
-	engine->irq_disable(engine);
-	spin_unlock(&engine->i915->irq_lock);
+	if (engine->irq_disable) {
+		spin_lock(&engine->i915->irq_lock);
+		engine->irq_disable(engine);
+		spin_unlock(&engine->i915->irq_lock);
+	}
 }
 
 void __intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine)