diff --git a/include/circt/Dialect/Ibis/CMakeLists.txt b/include/circt/Dialect/Ibis/CMakeLists.txt
index d45735b8ea..51d1012fd5 100644
--- a/include/circt/Dialect/Ibis/CMakeLists.txt
+++ b/include/circt/Dialect/Ibis/CMakeLists.txt
@@ -11,3 +11,9 @@ mlir_tablegen(IbisInterfaces.h.inc -gen-op-interface-decls)
 mlir_tablegen(IbisInterfaces.cpp.inc -gen-op-interface-defs)
 add_public_tablegen_target(MLIRIbisInterfacIbisncGen)
 add_dependencies(circt-headers MLIRIbisInterfacIbisncGen)
+
+set(LLVM_TARGET_DEFINITIONS Ibis.td)
+mlir_tablegen(IbisEnums.h.inc -gen-enum-decls)
+mlir_tablegen(IbisEnums.cpp.inc -gen-enum-defs)
+add_public_tablegen_target(MLIRIbisEnumsIncGen)
+add_dependencies(circt-headers MLIRIbisEnumsIncGen)
diff --git a/include/circt/Dialect/Ibis/IbisDialect.h b/include/circt/Dialect/Ibis/IbisDialect.h
index da0016d732..7607eeb4eb 100644
--- a/include/circt/Dialect/Ibis/IbisDialect.h
+++ b/include/circt/Dialect/Ibis/IbisDialect.h
@@ -14,4 +14,7 @@
 // Pull in the dialect definition.
 #include "circt/Dialect/Ibis/IbisDialect.h.inc"
 
+// Pull in all enum type definitions and utility function declarations.
+#include "circt/Dialect/Ibis/IbisEnums.h.inc"
+
 #endif // CIRCT_DIALECT_IBIS_IBISDIALECT_H
diff --git a/include/circt/Dialect/Ibis/IbisOps.td b/include/circt/Dialect/Ibis/IbisOps.td
index b7064acb51..dc311363b7 100644
--- a/include/circt/Dialect/Ibis/IbisOps.td
+++ b/include/circt/Dialect/Ibis/IbisOps.td
@@ -346,7 +346,7 @@ def PortReadOp : IbisOp<"port.read", [
 
 class InnerTypeToPortRefTypeConstraint<string lhs, string rhs>
   : TypesMatchWith<"the type of the lhs value dictates the rhs portref type",
-    lhs, rhs, "PortRefType::get($_ctxt, $_self)">;
+    lhs, rhs, "PortRefType::get($_ctxt, $_self, ibis::Direction::Input)">;
 
 def PortWriteOp : IbisOp<"port.write", [
       InnerTypeToPortRefTypeConstraint<"value", "port">
diff --git a/include/circt/Dialect/Ibis/IbisTypes.h b/include/circt/Dialect/Ibis/IbisTypes.h
index 7835a0c241..63f6e7af90 100644
--- a/include/circt/Dialect/Ibis/IbisTypes.h
+++ b/include/circt/Dialect/Ibis/IbisTypes.h
@@ -9,6 +9,7 @@
 #ifndef CIRCT_DIALECT_IBIS_IBISTYPES_H
 #define CIRCT_DIALECT_IBIS_IBISTYPES_H
 
+#include "circt/Dialect/Ibis/IbisDialect.h"
 #include "circt/Support/LLVM.h"
 #include "mlir/IR/BuiltinAttributes.h"
 #include "mlir/IR/Types.h"
diff --git a/include/circt/Dialect/Ibis/IbisTypes.td b/include/circt/Dialect/Ibis/IbisTypes.td
index 4cb11593ad..530f883e07 100644
--- a/include/circt/Dialect/Ibis/IbisTypes.td
+++ b/include/circt/Dialect/Ibis/IbisTypes.td
@@ -11,6 +11,7 @@
 
 include "circt/Dialect/Ibis/IbisDialect.td"
 include "mlir/IR/AttrTypeBase.td"
+include "mlir/IR/EnumAttr.td"
 
 class IbisTypeDef<string name> : TypeDef<IbisDialect, name> { }
 
@@ -52,10 +53,17 @@ def OpaqueScopeRefType : Type<
   BuildableType<"$_builder.getType<ibis::ScopeRefType>()"> {
 }
 
+def Input : I32EnumAttrCase<"Input", 0, "in">;
+def Output : I32EnumAttrCase<"Output", 1, "out">;
+def Direction : I32EnumAttr<"Direction", "Ibis port direction",
+  [Input, Output]> {
+  let cppNamespace = "::circt::ibis";
+}
+
 def PortRefType : IbisTypeDef<"PortRef"> {
   let mnemonic = "portref";
-  let parameters = (ins "TypeAttr":$portTypeAttr);
-  let assemblyFormat = "`<` $portTypeAttr  `>`";
+  let parameters = (ins "TypeAttr":$portTypeAttr, "ibis::Direction":$direction);
+  let assemblyFormat = "`<` $direction $portTypeAttr  `>`";
   let description = [{
     A reference to an Ibis port.
   }];
@@ -67,8 +75,8 @@ def PortRefType : IbisTypeDef<"PortRef"> {
   }];
 
   let builders = [
-    TypeBuilder<(ins "Type":$t), [{
-      return $_get($_ctxt, TypeAttr::get(t));
+    TypeBuilder<(ins "Type":$t, "ibis::Direction":$d), [{
+      return $_get($_ctxt, TypeAttr::get(t), d);
     }]>
   ];
 }
diff --git a/lib/Dialect/Ibis/IbisDialect.cpp b/lib/Dialect/Ibis/IbisDialect.cpp
index 2d7e573b3d..f5ba970739 100644
--- a/lib/Dialect/Ibis/IbisDialect.cpp
+++ b/lib/Dialect/Ibis/IbisDialect.cpp
@@ -24,3 +24,6 @@ void IbisDialect::initialize() {
 #include "circt/Dialect/Ibis/Ibis.cpp.inc"
       >();
 }
+
+// Provide implementations for the enums we use.
+#include "circt/Dialect/Ibis/IbisEnums.cpp.inc"
diff --git a/test/Dialect/Ibis/errors.mlir b/test/Dialect/Ibis/errors.mlir
index a4de7f8a82..0e703a7373 100644
--- a/test/Dialect/Ibis/errors.mlir
+++ b/test/Dialect/Ibis/errors.mlir
@@ -34,7 +34,7 @@ ibis.class @C {
 ibis.class @MissingPort {
   %this = ibis.this @MissingPort
   // expected-error @+1 {{'ibis.get_port' op port '@C_in' does not exist in MissingPort}}
-  %c_in = ibis.get_port %this, @C_in : !ibis.scoperef<@MissingPort> -> !ibis.portref<i1>
+  %c_in = ibis.get_port %this, @C_in : !ibis.scoperef<@MissingPort> -> !ibis.portref<in i1>
 }
 
 // -----
@@ -43,7 +43,7 @@ ibis.class @PortTypeMismatch {
   %this = ibis.this @PortTypeMismatch
   ibis.port.input @in : i1
   // expected-error @+1 {{'ibis.get_port' op symbol '@in' refers to a port of type 'i1', but this op has type 'i2'}}
-  %c_in = ibis.get_port %this, @in : !ibis.scoperef<@PortTypeMismatch> -> !ibis.portref<i2>
+  %c_in = ibis.get_port %this, @in : !ibis.scoperef<@PortTypeMismatch> -> !ibis.portref<in i2>
 }
 
 // -----
diff --git a/test/Dialect/Ibis/round-trip.mlir b/test/Dialect/Ibis/round-trip.mlir
index 9ad00c6907..79b7f3af6d 100644
--- a/test/Dialect/Ibis/round-trip.mlir
+++ b/test/Dialect/Ibis/round-trip.mlir
@@ -13,21 +13,21 @@
 // CHECK-NEXT:    %1 = ibis.instance @a, @A 
 // CHECK-NEXT:    %2 = ibis.get_parent_of_ref %1 : !ibis.scoperef<@A> -> !ibis.scoperef
 // CHECK-NEXT:    %3 = ibis.get_instance_in_ref @a : @A in %0 : !ibis.scoperef<@C> 
-// CHECK-NEXT:    %4 = ibis.get_port %1, @A_in : !ibis.scoperef<@A> -> !ibis.portref<i1>
+// CHECK-NEXT:    %4 = ibis.get_port %1, @A_in : !ibis.scoperef<@A> -> !ibis.portref<in i1>
 // CHECK-NEXT:    %5 = ibis.get_instance_in_ref @a : @A in %2 : !ibis.scoperef 
 // CHECK-NEXT:    ibis.container @D {
 // CHECK-NEXT:      %6 = ibis.this @D 
 // CHECK-NEXT:      %7 = ibis.get_parent_of_ref %6 : !ibis.scoperef<@D> -> !ibis.scoperef<@C>
-// CHECK-NEXT:      %8 = ibis.get_port %7, @C_in : !ibis.scoperef<@C> -> !ibis.portref<i1>
-// CHECK-NEXT:      %9 = ibis.get_port %7, @C_out : !ibis.scoperef<@C> -> !ibis.portref<i1>
+// CHECK-NEXT:      %8 = ibis.get_port %7, @C_in : !ibis.scoperef<@C> -> !ibis.portref<in i1>
+// CHECK-NEXT:      %9 = ibis.get_port %7, @C_out : !ibis.scoperef<@C> -> !ibis.portref<out i1>
 // CHECK-NEXT:      %true = hw.constant true
-// CHECK-NEXT:      ibis.port.write %9, %true : i1
-// CHECK-NEXT:      %10 = ibis.port.read %8 : !ibis.portref<i1>
+// CHECK-NEXT:      ibis.port.write %8, %true : i1
+// CHECK-NEXT:      %10 = ibis.port.read %9 : !ibis.portref<out i1>
 // CHECK-NEXT:      %11 = ibis.get_instance_in_ref @a : @A in %7 : !ibis.scoperef<@C> 
-// CHECK-NEXT:      %12 = ibis.get_port %11, @A_in : !ibis.scoperef<@A> -> !ibis.portref<i1>
-// CHECK-NEXT:      %13 = ibis.get_port %11, @A_out : !ibis.scoperef<@A> -> !ibis.portref<i1>
+// CHECK-NEXT:      %12 = ibis.get_port %11, @A_in : !ibis.scoperef<@A> -> !ibis.portref<in i1>
+// CHECK-NEXT:      %13 = ibis.get_port %11, @A_out : !ibis.scoperef<@A> -> !ibis.portref<out i1>
 // CHECK-NEXT:      ibis.port.write %12, %10 : i1
-// CHECK-NEXT:      %14 = ibis.port.read %13 : !ibis.portref<i1>
+// CHECK-NEXT:      %14 = ibis.port.read %13 : !ibis.portref<out i1>
 // CHECK-NEXT:    }
 // CHECK-NEXT:  }
 
@@ -48,7 +48,7 @@ ibis.class @C {
   // Test get parent/child
   %parent = ibis.get_parent_of_ref %a : !ibis.scoperef<@A> -> !ibis.scoperef
   %child = ibis.get_instance_in_ref @a : @A in %this : !ibis.scoperef<@C>
-  %a_in_cp = ibis.get_port %a, @A_in : !ibis.scoperef<@A> -> !ibis.portref<i1>
+  %a_in_cp = ibis.get_port %a, @A_in : !ibis.scoperef<@A> -> !ibis.portref<in i1>
 
   // Test siblings
   %sibling = ibis.get_instance_in_ref @a : @A in %parent : !ibis.scoperef
@@ -57,17 +57,17 @@ ibis.class @C {
     %this_d = ibis.this @D
     %parent_C = ibis.get_parent_of_ref %this_d : !ibis.scoperef<@D> -> !ibis.scoperef<@C>
     // Test local read/writes
-    %c_in_p = ibis.get_port %parent_C, @C_in : !ibis.scoperef<@C> -> !ibis.portref<i1>
-    %c_out_p = ibis.get_port %parent_C, @C_out : !ibis.scoperef<@C> -> !ibis.portref<i1>
+    %c_in_p = ibis.get_port %parent_C, @C_in : !ibis.scoperef<@C> -> !ibis.portref<in i1>
+    %c_out_p = ibis.get_port %parent_C, @C_out : !ibis.scoperef<@C> -> !ibis.portref<out i1>
     %true = hw.constant true
-    ibis.port.write %c_out_p, %true : i1
-    %c_out = ibis.port.read %c_in_p : !ibis.portref<i1>
+    ibis.port.write %c_in_p, %true : i1
+    %c_out = ibis.port.read %c_out_p : !ibis.portref<out i1>
 
     // Test cross-container read/writes
     %a_in_parent = ibis.get_instance_in_ref @a : @A in %parent_C : !ibis.scoperef<@C>
-    %a_in_p = ibis.get_port %a_in_parent, @A_in : !ibis.scoperef<@A> -> !ibis.portref<i1>
-    %a_out_p = ibis.get_port %a_in_parent, @A_out : !ibis.scoperef<@A> -> !ibis.portref<i1>
+    %a_in_p = ibis.get_port %a_in_parent, @A_in : !ibis.scoperef<@A> -> !ibis.portref<in i1>
+    %a_out_p = ibis.get_port %a_in_parent, @A_out : !ibis.scoperef<@A> -> !ibis.portref<out i1>
     ibis.port.write %a_in_p, %c_out : i1
-    %a_out = ibis.port.read %a_out_p : !ibis.portref<i1>
+    %a_out = ibis.port.read %a_out_p : !ibis.portref<out i1>
   }
 }