zephyr: test: userspace: add test_mailbox for sof/mailbox.h

Add a user-space test for sof/mailbox.h interface usage. The test covers
current usage of mailbox by SOF audio pipeline code.

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

Author: kv2019i

zephyr/test/CMakeLists.txt

@@ -15,3 +15,7 @@ if (CONFIG_SOF_BOOT_TEST_STANDALONE AND CONFIG_SOF_USERSPACE_INTERFACE_DMA)
               zephyr_library_sources(userspace/test_intel_ssp_dai.c)
        endif()
 endif()
+
+if (CONFIG_SOF_BOOT_TEST_STANDALONE AND CONFIG_USERSPACE)
+  zephyr_library_sources(userspace/test_mailbox.c)
+endif()

zephyr/test/userspace/README.md

@@ -12,6 +12,8 @@ Available tests:
    - Test Zephyr DAI interface, together with SOF DMA
      wrapper from a user thread. Mimics the call flows done in
      sof/src/audio/dai-zephyr.c. Use cavstool.py as host runner.
+- test_mailbox.c
+   - Test use of sof/mailbox.h interface from a Zephyr user thread.
 
 Building for Intel Panther Lake:
 ./scripts/xtensa-build-zephyr.py --cmake-args=-DCONFIG_SOF_BOOT_TEST_STANDALONE=y \

zephyr/test/userspace/test_mailbox.c

@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Copyright(c) 2026 Intel Corporation.
+ */
+
+/*
+ * Test case for sof/mailbox.h interface use from a Zephyr user
+ * thread.
+ */
+
+#include <sof/boot_test.h>
+#include <sof/lib/mailbox.h>
+#include <rtos/userspace_helper.h>
+
+#include <zephyr/kernel.h>
+#include <zephyr/ztest.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/app_memory/app_memdomain.h>
+
+#include <ipc4/fw_reg.h> /* mailbox definitions */
+
+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 mailbox_write_to_pipeline_regs(void)
+{
+	unsigned int offset = offsetof(struct ipc4_fw_registers, pipeline_regs);
+	struct ipc4_pipeline_registers pipe_reg;
+
+	/*
+	 * IPC4 pipe_reg struct used for test, but this test also
+	 * works for IPC3 targets.
+	 */
+	pipe_reg.stream_start_offset = (uint64_t)-1;
+	pipe_reg.stream_end_offset = (uint64_t)-1;
+
+	LOG_INF("Write to sw_regs mailbox at offset %u", offset);
+
+	mailbox_sw_regs_write(offset, &pipe_reg, sizeof(pipe_reg));
+}
+
+static void mailbox_test_thread(void *p1, void *p2, void *p3)
+{
+	zassert_true(k_is_user_context(), "isn't user");
+
+	LOG_INF("SOF thread %s (%s)",
+		k_is_user_context() ? "UserSpace!" : "privileged mode.",
+		CONFIG_BOARD_TARGET);
+
+	mailbox_write_to_pipeline_regs();
+}
+
+static void mailbox_test(void)
+{
+	struct k_mem_domain domain;
+	int ret = k_mem_domain_init(&domain, 0, NULL);
+
+	zassert_equal(ret, 0);
+
+	k_thread_create(&user_thread, user_stack, USER_STACKSIZE,
+			mailbox_test_thread, NULL, NULL, NULL,
+			-1, K_USER, K_FOREVER);
+
+	LOG_INF("set up user access to mailbox");
+
+	ret = user_access_to_mailbox(&domain, &user_thread);
+	zassert_equal(ret, 0);
+
+	k_thread_start(&user_thread);
+
+	LOG_INF("user started, waiting in kernel until test complete");
+
+	k_thread_join(&user_thread, K_FOREVER);
+}
+
+ZTEST(userspace_mailbox, mailbox_test)
+{
+	/* first test from kernel */
+	mailbox_write_to_pipeline_regs();
+
+	/* then full test in userspace */
+	mailbox_test();
+
+	ztest_test_pass();
+}
+
+ZTEST_SUITE(userspace_mailbox, NULL, NULL, NULL, NULL, NULL);
+
+/**
+ * SOF main has booted up and IPC handling is stopped.
+ * Run test suites with ztest_run_all.
+ */
+static int run_tests(void)
+{
+	ztest_run_test_suite(userspace_mailbox, false, 1, 1, NULL);
+	return 0;
+}
+
+SYS_INIT(run_tests, APPLICATION, 99);