[dif] Add empty soc_proxy DIF

Thid DIF exports not function beyond the autogenerated one. It is
necessary to have it so that the isr_tstutils and the autogenerated
plic tests can compile on Darjeeling.

Signed-off-by: Amaury Pouly <[email protected]>

sw/device/lib/dif/BUILD

@@ -1344,6 +1344,27 @@ cc_test(
     ],
 )
 
+cc_library(
+    name = "soc_proxy",
+    srcs = [
+        "//sw/device/lib/dif/autogen:soc_proxy_hdr",
+        "//sw/device/lib/dif/autogen:soc_proxy_src",
+    ],
+    hdrs = [
+        "dif_soc_proxy.h",
+    ],
+    deps = [
+        ":base",
+        "//hw/top:dt_soc_proxy",
+        "//hw/top:soc_proxy_c_regs",
+        "//sw/device/lib/base:bitfield",
+        "//sw/device/lib/base:macros",
+        "//sw/device/lib/base:memory",
+        "//sw/device/lib/base:mmio",
+        "//sw/device/lib/base:multibits",
+    ],
+)
+
 cc_library(
     name = "all_difs",
     deps = flatten([

sw/device/lib/dif/defs.bzl

@@ -5,5 +5,4 @@
 # This is the list of all IPs that do not have a DIF.
 IPS_WITHOUT_DIF = [
     "ast",
-    "soc_proxy",
-]
+]

sw/device/lib/dif/dif_soc_proxy.h

@@ -0,0 +1,22 @@
+// Copyright lowRISC contributors (OpenTitan project).
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+#ifndef OPENTITAN_SW_DEVICE_LIB_DIF_DIF_SOC_PROXY_H_
+#define OPENTITAN_SW_DEVICE_LIB_DIF_DIF_SOC_PROXY_H_
+
+/**
+ * This is an empty DIF. It's sole purpose is to export the autogenerated DIF
+ * functions so that the PLIC tests and ISR testutils can use it.
+ */
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "sw/device/lib/base/macros.h"
+#include "sw/device/lib/base/mmio.h"
+#include "sw/device/lib/dif/dif_base.h"
+
+#include "sw/device/lib/dif/autogen/dif_soc_proxy_autogen.h"
+
+#endif  // OPENTITAN_SW_DEVICE_LIB_DIF_DIF_SOC_PROXY_H_