tests/kernel: Add test for CONFIG_SMP_BOOT_DELAY

This feature is in tree and used by the SOF app, but we don't have a
local test for it.  Add one, including a case to track regressions in
a known failure mode (where the second CPU wouldn't get its IDC
interrupts set up correctly if spawned at runtime).

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>

tests/kernel/smp_boot_delay/CMakeLists.txt

@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.20.0)
+find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
+project(smp_boot_delay)
+
+target_sources(app PRIVATE src/main.c)

tests/kernel/smp_boot_delay/prj.conf

@@ -0,0 +1,3 @@
+CONFIG_ZTEST=y
+CONFIG_SMP=y
+CONFIG_SMP_BOOT_DELAY=y

tests/kernel/smp_boot_delay/src/main.c

@@ -0,0 +1,84 @@
+/* Copyright (c) 2021 Intel Corporation.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr.h>
+#include <ztest.h>
+
+/* Experimentally 10ms is enough time to get the second CPU to run on
+ * all known platforms.
+ */
+#define CPU_START_DELAY 10000
+
+/* IPIs happen  much faster than CPU startup */
+#define CPU_IPI_DELAY 100
+
+BUILD_ASSERT(CONFIG_SMP);
+BUILD_ASSERT(CONFIG_SMP_BOOT_DELAY);
+BUILD_ASSERT(CONFIG_KERNEL_COHERENCE);
+BUILD_ASSERT(CONFIG_MP_NUM_CPUS > 1);
+
+#define STACKSZ 2048
+char stack[STACKSZ];
+
+volatile bool mp_flag;
+
+struct k_thread cpu1_thr;
+K_THREAD_STACK_DEFINE(thr_stack, STACKSZ);
+
+extern void z_smp_start_cpu(int id);
+
+static void thread_fn(void *a, void *b, void *c)
+{
+	mp_flag = true;
+}
+
+void test_smp_boot_delay(void)
+{
+	/* Create a thread of lower priority.  This could run on
+	 * another CPU if it was available, but will not preempt us
+	 * unless we block (which we do not).
+	 */
+	k_thread_create(&cpu1_thr, thr_stack, K_THREAD_STACK_SIZEOF(thr_stack),
+			thread_fn, NULL, NULL, NULL,
+			1, 0, K_NO_WAIT);
+
+	/* Make sure that thread has not run (because the cpu is halted) */
+	k_busy_wait(CPU_START_DELAY);
+	zassert_false(mp_flag, "CPU1 must not be running yet");
+
+	/* Start the second CPU */
+	z_smp_start_cpu(1);
+
+	/* Verify the thread ran */
+	k_busy_wait(CPU_START_DELAY);
+	zassert_true(mp_flag, "CPU1 did not start");
+
+	k_thread_abort(&cpu1_thr);
+}
+
+void test_post_boot_ipi(void)
+{
+	/* Spawn the same thread to do the same thing, but this time
+	 * expect that the thread is going to run synchronously on the
+	 * other CPU as soon as its created.  Intended to test whether
+	 * IPIs were correctly set up on the runtime-launched CPU.
+	 */
+	mp_flag = false;
+	k_thread_create(&cpu1_thr, thr_stack, K_THREAD_STACK_SIZEOF(thr_stack),
+			thread_fn, NULL, NULL, NULL,
+			1, 0, K_NO_WAIT);
+
+	k_busy_wait(CPU_IPI_DELAY);
+	zassert_true(mp_flag, "CPU1 did not start thread via IPI");
+}
+
+void test_main(void)
+{
+	ztest_test_suite(smp_boot_delay,
+			 ztest_unit_test(test_smp_boot_delay),
+			 ztest_unit_test(test_post_boot_ipi)
+			 );
+
+	ztest_run_test_suite(smp_boot_delay);
+}

tests/kernel/smp_boot_delay/testcase.yaml

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+tests:
+  kernel.multiprocessing.smp_boot_delay:
+    tags: kernel smp
+    platform_allow: intel_adsp_cavs15 intel_adsp_cavs18 intel_adsp_cavs20 intel_adsp_cavs25