util: add DontTouch trait with dontTouchPorts method

src/main/scala/system/ExampleRocketSystem.scala

@@ -6,6 +6,7 @@ import Chisel._
 import freechips.rocketchip.config.Parameters
 import freechips.rocketchip.coreplex._
 import freechips.rocketchip.devices.tilelink._
+import freechips.rocketchip.util.DontTouch
 
 /** Example Top with periphery devices and ports, and a Rocket coreplex */
 class ExampleRocketSystem(implicit p: Parameters) extends RocketCoreplex
@@ -25,3 +26,4 @@ class ExampleRocketSystemModule[+L <: ExampleRocketSystem](_outer: L) extends Ro
     with HasMasterAXI4MMIOPortModuleImp
     with HasSlaveAXI4PortModuleImp
     with HasPeripheryBootROMModuleImp
+    with DontTouch

src/main/scala/system/TestHarness.scala

@@ -14,6 +14,7 @@ class TestHarness()(implicit p: Parameters) extends Module {
   val dut = Module(LazyModule(new ExampleRocketSystem).module)
   dut.reset := reset | dut.debug.ndreset
 
+  dut.dontTouchPorts()
   dut.tieOffInterrupts()
   dut.connectSimAXIMem()
   dut.connectSimAXIMMIO()

src/main/scala/util/Misc.scala

@@ -4,6 +4,7 @@
 package freechips.rocketchip.util
 
 import Chisel._
+import chisel3.experimental.{dontTouch, RawModule}
 import freechips.rocketchip.config.Parameters
 import scala.math._
 
@@ -21,6 +22,21 @@ class ParameterizedBundle(implicit p: Parameters) extends Bundle {
   }
 }
 
+// TODO: replace this with an implicit class when @chisel unprotects dontTouchPorts
+trait DontTouch {
+  self: RawModule =>
+
+  /** Marks every port as don't touch
+    *
+    * @note This method can only be called after the Module has been fully constructed
+    *   (after Module(...))
+    */
+  def dontTouchPorts(): this.type = {
+    self.getModulePorts.foreach(dontTouch(_))
+    self
+  }
+}
+
 trait Clocked extends Bundle {
   val clock = Clock()
   val reset = Bool()