zephyr: tests: userspace: add test for cache ops via syscalls

Add simple tests that call cache invalidate and flush from a user-space
thread.

This does not currently have any negative tests (attempt to invalidate
an buffer the user space thread does not have access to), as these
currently result in kernel oops on xtensa.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

Author: kv2019i

zephyr/test/CMakeLists.txt

@@ -6,6 +6,7 @@ endif()
 
 if (CONFIG_ACE_VERSION_3_0)
 	zephyr_library_sources_ifdef(CONFIG_SOF_BOOT_TEST
+		userspace/cache.c
 		userspace/local_lock.c
 	)
 endif()

zephyr/test/userspace/cache.c

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Copyright(c) 2025 Intel Corporation.
+ */
+
+#include <sof/boot_test.h>
+
+#include <zephyr/kernel.h>
+#include <rtos/cache.h>
+#include <zephyr/ztest.h>
+#include <zephyr/logging/log.h>
+
+LOG_MODULE_DECLARE(sof_boot_test, LOG_LEVEL_DBG);
+
+#define USER_STACKSIZE	2048
+
+static struct k_thread user_thread;
+static K_THREAD_STACK_DEFINE(user_stack, USER_STACKSIZE);
+
+static void user_function(void *p1, void *p2, void *p3)
+{
+	char stack_buf[64];
+
+	__ASSERT(k_is_user_context(), "isn't user");
+
+	LOG_INF("SOF thread %s (%s)",
+		k_is_user_context() ? "UserSpace!" : "privileged mode.",
+		CONFIG_BOARD_TARGET);
+
+	/*
+	 * Use rtos/cache.h calls as these are also used by
+	 * src/audio code.
+	 */
+
+	dcache_writeback_region(stack_buf, sizeof(stack_buf));
+
+	dcache_invalidate_region(stack_buf, sizeof(stack_buf));
+}
+
+static void test_user_thread_cache(void)
+{
+	k_thread_create(&user_thread, user_stack, USER_STACKSIZE,
+			user_function, NULL, NULL, NULL,
+			-1, K_USER, K_MSEC(0));
+	k_thread_join(&user_thread, K_FOREVER);
+}
+
+ZTEST(sof_boot, user_space_cache)
+{
+	test_user_thread_cache();
+
+	ztest_test_pass();
+}