[tests] Verify ability to sleep the CPU

The self-test suite does not currently ever attempt to sleep the CPU.
This is an operation that may fail (e.g. by attempting to execute a
privileged instruction while running as a Linux userspace binary, or
by halting the CPU with all interrupts disabled).

Add a trivial self-test to exercise the ability to sleep the CPU
without crashing or halting forever.

Inspired-by: Xiaotian Wu <wuxiaotian@loongson.cn>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/tests/nap_test.c

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2023 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
+
+/** @file
+ *
+ * CPU sleeping test
+ *
+ */
+
+/* Forcibly enable assertions */
+#undef NDEBUG
+
+#include <ipxe/nap.h>
+#include <ipxe/test.h>
+
+/**
+ * Perform CPU sleeping self-test
+ *
+ */
+static void nap_test_exec ( void ) {
+
+	/* Check that we can sleep without crashing or halting forever */
+	cpu_nap();
+	ok ( 1 );
+}
+
+/** CPU sleeping self-test */
+struct self_test nap_test __self_test = {
+	.name = "nap",
+	.exec = nap_test_exec,
+};

src/tests/tests.c

@@ -80,3 +80,4 @@ REQUIRE_OBJECT ( acpi_test );
 REQUIRE_OBJECT ( hmac_test );
 REQUIRE_OBJECT ( dhe_test );
 REQUIRE_OBJECT ( gcm_test );
+REQUIRE_OBJECT ( nap_test );