whiterun: Implement unit test for custom fan duty control

Whiterun uses a custom fan duty control logic.
Implement a unit test for it.
Two global structures that describe fan and its state were mocked.
The test makes a really simple fan pseudo-emulation, i.e. after fan duty
is change the RPM is adjusted taking inertia into account.

BUG=b:279493434
TEST=./twister -i -T zephyr/test/skyrim/

Change-Id: Id32dd8c8ee76420a83de25b23837b8df35ecabbb
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/4479372
Tested-by: Kornel Dulęba <korneld@google.com>
Reviewed-by: Keith Short <keithshort@chromium.org>
Commit-Queue: Kornel Dulęba <korneld@google.com>

3 files changed, 173 insertions, 1 deletions

diff --git a/zephyr/test/skyrim/testcase.yaml b/zephyr/test/skyrim/testcase.yaml
index 403b8f7e6c..1dfae464cf 100644
--- a/zephyr/test/skyrim/testcase.yaml
+++ b/zephyr/test/skyrim/testcase.yaml
@@ -126,3 +126,9 @@ tests:
     extra_configs:
     - CONFIG_TEST_BOARD_WINTERHOLD=y
     - CONFIG_TEST_BOARD_USB_MUX_CONFIG_CUSTOM=y
+
+  skyrim.winterhold.fan:
+    extra_configs:
+    - CONFIG_TEST_BOARD_WINTERHOLD=y
+    - CONFIG_TEST_BOARD_FAN=y
+    - CONFIG_TEST_BOARD_FAN_CUSTOM=y
diff --git a/zephyr/test/skyrim/tests/winterhold/CMakeLists.txt b/zephyr/test/skyrim/tests/winterhold/CMakeLists.txt
index 673b09bdcd..39ded69058 100644
--- a/zephyr/test/skyrim/tests/winterhold/CMakeLists.txt
+++ b/zephyr/test/skyrim/tests/winterhold/CMakeLists.txt
@@ -3,4 +3,5 @@
 # found in the LICENSE file.
 
 target_sources(app PRIVATE src/common.c)
-target_sources_ifdef(CONFIG_TEST_BOARD_PPC_CONFIG app PRIVATE src/ppc_config.c)
\ No newline at end of file
+target_sources_ifdef(CONFIG_TEST_BOARD_PPC_CONFIG app PRIVATE src/ppc_config.c)
+target_sources_ifdef(CONFIG_TEST_BOARD_FAN_CUSTOM app PRIVATE src/fan.c)
diff --git a/zephyr/test/skyrim/tests/winterhold/src/fan.c b/zephyr/test/skyrim/tests/winterhold/src/fan.c
new file mode 100644
index 0000000000..a7af0d2da1
--- /dev/null
+++ b/zephyr/test/skyrim/tests/winterhold/src/fan.c
@@ -0,0 +1,165 @@
+/* Copyright 2023 The ChromiumOS Authors
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include <zephyr/fff.h>
+#include <zephyr/kernel.h>
+#include <zephyr/logging/log.h>
+#include <zephyr/ztest.h>
+
+#include <cros_board_info.h>
+#include <cros_cbi.h>
+#include <fan.h>
+#include <hooks.h>
+
+FAKE_VOID_FUNC(fan_set_duty, int, int);
+FAKE_VALUE_FUNC(int, fan_get_duty, int);
+
+struct fan_conf conf;
+struct fan_rpm rpm;
+
+const struct fan_t fans[1] = { { .conf = &conf, .rpm = &rpm } };
+struct fan_data fan_data[1];
+
+K_TIMER_DEFINE(ktimer, NULL, NULL);
+
+static void fan_set_duty_mock(int ch, int duty)
+{
+	zassert_equal(ch, 0);
+	zassert_between_inclusive(duty, 0, 100);
+
+	fan_data[ch].pwm_percent = duty;
+}
+
+static int fan_get_duty_mock(int ch)
+{
+	zassert_equal(ch, 0);
+	zassert_between_inclusive(fan_data[ch].pwm_percent, 0, 100);
+
+	return fan_data[ch].pwm_percent;
+}
+
+static int duty_to_rpm(int duty)
+{
+	const float ratio = 0.015;
+
+	zassert_between_inclusive(duty, 0, 100);
+
+	return (int)((float)duty / ratio);
+}
+
+static void fan_tick(void)
+{
+	int rpm_diff;
+	int duty;
+
+	duty = fan_data[0].pwm_percent;
+
+	rpm_diff = duty_to_rpm(duty) - fan_data[0].rpm_actual;
+
+	/* Clamp rpm_diff. This essentially emulates fan inertia. */
+	if (rpm_diff > 0)
+		rpm_diff = MIN(rpm_diff, 500);
+	if (rpm_diff < 0)
+		rpm_diff = MAX(rpm_diff, -500);
+
+	fan_data[0].rpm_actual += rpm_diff;
+}
+
+static void fan_test_begin(void *fixture)
+{
+	ARG_UNUSED(fixture);
+	RESET_FAKE(fan_set_duty);
+	RESET_FAKE(fan_get_duty);
+
+	fan_set_duty_fake.custom_fake = fan_set_duty_mock;
+	fan_get_duty_fake.custom_fake = fan_get_duty_mock;
+
+	/*
+	 * This is normally read from DT.
+	 * The problem is that we don't want to pull the entire fan framework
+	 * for this test. Instead initialize it here.
+	 * All the values come from
+	 * zephyr/program/skyrim/winterhold/project.overlay.
+	 */
+	memset(&conf, 0, sizeof(conf));
+	memset(&rpm, 0, sizeof(rpm));
+
+	rpm.rpm_max = 4800;
+	rpm.rpm_deviation = 3;
+
+	memset(&fan_data[0], 0, sizeof(fan_data[0]));
+}
+
+/* Only FAN 0 should be supported. */
+ZTEST(fan, test_fan_invalid_arg)
+{
+	enum fan_status status;
+
+	status = board_override_fan_control_duty(1);
+	zassert_equal(status, FAN_STATUS_FRUSTRATED);
+}
+
+/*
+ * Check whether we can ramp up into rpm_max in 5s.
+ * The time limit is selected on a per board basis.
+ * It depends on the thermal capacity of the radiator and CPU TDP.
+ * Basically we want to ensure that fan ramps up fast enough
+ * to prevent the CPU from thermal throttling.
+ */
+ZTEST(fan, test_fan_max_rpm)
+{
+	enum fan_status status;
+	int deviation;
+
+	fan_data[0].rpm_target = rpm.rpm_max;
+	k_timer_start(&ktimer, K_SECONDS(5), K_NO_WAIT);
+
+	while (k_timer_remaining_ticks(&ktimer) != 0) {
+		status = board_override_fan_control_duty(0);
+		zassert_not_equal(status, FAN_STATUS_FRUSTRATED);
+		fan_tick();
+		k_sleep(K_TICKS(1));
+	}
+
+	deviation = rpm.rpm_deviation * rpm.rpm_max / 100;
+	zassert_true(fan_set_duty_fake.call_count > 1);
+	zassert_within(fan_data[0].rpm_actual, rpm.rpm_max, deviation);
+	zassert_equal(status, FAN_STATUS_LOCKED);
+}
+
+/* Check for FAN_STATUS_STOPPED when the fan is in fact stopped. */
+ZTEST(fan, test_fan_off)
+{
+	enum fan_status status;
+
+	status = board_override_fan_control_duty(0);
+	zassert_equal(status, FAN_STATUS_STOPPED);
+	zassert_equal(fan_set_duty_fake.call_count, 0);
+}
+
+/* If we can't achieve selected RPM, FAN_STATUS_FRUSTRATED is expected. */
+ZTEST(fan, test_fan_frustrated_max)
+{
+	enum fan_status status;
+
+	/*
+	 * 10 seconds should be more than enough for implementation to realize
+	 * that it can't get up to 10k RPM
+	 */
+	fan_data[0].rpm_target = 10000;
+	k_timer_start(&ktimer, K_SECONDS(10), K_NO_WAIT);
+
+	while (k_timer_remaining_ticks(&ktimer) != 0) {
+		status = board_override_fan_control_duty(0);
+		if (status == FAN_STATUS_FRUSTRATED)
+			break;
+
+		fan_tick();
+		k_sleep(K_TICKS(1));
+	}
+	zassert_true(fan_set_duty_fake.call_count > 1);
+	zassert_equal(status, FAN_STATUS_FRUSTRATED);
+}
+
+ZTEST_SUITE(fan, NULL, NULL, fan_test_begin, NULL, NULL);