zephyr: shell: add initial SOF custom commands

One of the benefits and common ways to use the Zephyr shell
subsystem is definition of application specific commands.

This commit adds the initial SOF custom command,
"sof test_inject_sched_gap". This new command allows to inject
scheduling gaps into low-latency timer scheduler execution,
using the domain_block() SOF interface. Optional argument
can be used to specify duration of the block in micro seconds.

The intent is to stress test a SOF configuration and test how
the system behaves when audio pipeline is briefly starved.

Example log of what is observed when test_inkect_sched_gap is
run:

[    0.052431] <inf> ll_schedule: zephyr_domain_thread_fn: ll core 0 timer avg 3674, max 4326, overruns 0
[    0.052831] <inf> ll_schedule: zephyr_domain_thread_fn: ll core 0 timer avg 3673, max 4318, overruns 0
~$
~$ sof test_inject_sched_gap 12000
[    0.052968] <inf> ll_schedule: zephyr_domain_block: Blocking LL scheduler
[    0.052973] <inf> ll_schedule: zephyr_domain_unblock: Unblocking LL scheduler
[    0.052973] <inf> host_comp: host_get_copy_bytes_normal: comp:1 0x10004 no bytes to copy, available samples: 0, free_samples: 384
[    0.053231] <inf> ll_schedule: zephyr_domain_thread_fn: ll core 0 timer avg 4074, max 437230, overruns 1

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

zephyr/CMakeLists.txt

@@ -982,6 +982,10 @@ zephyr_library_sources_ifdef(CONFIG_SOF_BOOT_TEST
        boot_test.c
 )
 
+zephyr_library_sources_ifdef(CONFIG_SHELL
+       sof_shell.c
+)
+
 zephyr_library_link_libraries(SOF)
 target_link_libraries(SOF INTERFACE zephyr_interface)
 

zephyr/sof_shell.c

@@ -0,0 +1,51 @@
+// SPDX-License-Identifier: BSD-3-Clause
+/*
+ * Copyright(c) 2024 Intel Corporation.
+ *
+ * Author: Kai Vehmanen <kai.vehmanen@linux.intel.com>
+ */
+
+#include <rtos/sof.h> /* sof_get() */
+#include <sof/schedule/ll_schedule_domain.h>
+
+#include <zephyr/kernel.h>
+#include <zephyr/sys/printk.h>
+#include <zephyr/shell/shell.h>
+
+#define SOF_TEST_INJECT_SCHED_GAP_USEC 1500
+
+static int cmd_sof_test_inject_sched_gap(const struct shell *sh,
+		       size_t argc, char *argv[])
+{
+	uint32_t block_time = SOF_TEST_INJECT_SCHED_GAP_USEC;
+	char *endptr = NULL;
+
+#ifndef CONFIG_CROSS_CORE_STREAM
+	shell_fprintf(sh, SHELL_NORMAL, "Domain blocking not supported, not reliable on SMP\n");
+#endif
+
+	domain_block(sof_get()->platform_timer_domain);
+
+	if (argc > 1) {
+		block_time = strtol(argv[1], &endptr, 0);
+		if (endptr == argv[1])
+			return -EINVAL;
+	}
+
+	k_busy_wait(block_time);
+
+	domain_unblock(sof_get()->platform_timer_domain);
+
+	return 0;
+}
+
+SHELL_STATIC_SUBCMD_SET_CREATE(sof_commands,
+	SHELL_CMD(test_inject_sched_gap, NULL,
+		  "Inject a gap to audio scheduling\n",
+		  cmd_sof_test_inject_sched_gap),
+
+	SHELL_SUBCMD_SET_END
+);
+
+SHELL_CMD_REGISTER(sof, &sof_commands,
+		   "SOF application commands", NULL);