fwk: create the temperature filter driver

Create the temperature filter driver to calculate the virtual
temperature.

example:
/ {
	named-temp-sensors {
		virtual_temp_sensor_memory: virtual-memory-f75303 {
			temp_host_warn = <108>;
			temp_host_high = <108>;
			temp_host_halt = <127>;
			temp_host_release_warn = <60>;
			temp_host_release_high = <60>;
			temp_host_release_halt = <122>;
			power-good-pin = <&gpio_slp_s3_l>;
			sensor = <&virtual_memory_f75303>;
			coefficients = <15 31 15 16384 (-31313) 14991>;
		};
	};
};

&i2c7_0 {
	virtual_memory_f75303: virtual_memory_f75303@4d {
		compatible = "cros-ec,temp-sensor-f75303";
		temperature-type = "F75303_IDX_REMOTE1";
		reg = <0x4d>;
	};
};

BRANCH=fwk-dogwood-27111
BUG=None
TEST=zmake build pass
TEST=add the virtual sensor node in the devicetree, can print
     the value in the ec console via command "temps"

Signed-off-by: Josh Tsai <Josh_Tsai@compal.com>

Author: Josh-Tsai

include/ec_commands.h

@@ -3778,6 +3778,12 @@ struct ec_thermal_config {
 	uint32_t temp_host_release[EC_TEMP_THRESH_COUNT]; /* release levels */
 	uint32_t temp_fan_off; /* no active cooling needed */
 	uint32_t temp_fan_max; /* max active cooling needed */
+	/**
+	 * (bug: 86ett7kn7)
+	 * TODO: should not add the new variable in host command struct
+	 * without cmd version
+	 */
+	int32_t coefficients[6]; /* coefficients to calculate the virtual temperature */
 } __ec_align4;
 
 /* Version 1 - get config for one sensor. */

zephyr/dts/bindings/temp/cros-ec,temp-sensors.yaml

@@ -72,3 +72,10 @@ child-binding:
       type: int
       description:
         Temperature release threshold in degrees C of thermal shutdown
+
+    coefficients:
+      type: array
+      description:
+        thermal_filter_update() uses six coefficients (b0, b1, b2, a0, a1, a2)
+        to calculate the virtual temperature.
+        Array values are all zero to disable virtual temperature.

zephyr/shim/include/temperature_filter.h

@@ -0,0 +1,38 @@
+/* Copyright 2022 The ChromiumOS Authors
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Low pass filter for on die temperature
+ */
+#ifndef __CROS_EC_TEMPERATURE_FILTER_H
+#define __CROS_EC_TEMPERATURE_FILTER_H
+
+#include "temp_sensor/temp_sensor.h"
+
+/**
+ * Check whether the temp sensor coefficients is zero or not.
+ *
+ * @param id temp sensor id
+ * @return true if support (coefficients none zero)
+ */
+bool temperature_filter_is_support(enum temp_sensor_id id);
+
+/**
+ * Return the virtual temperature.
+ *
+ * @param id temp sensor id
+ * @param temp_ptr the actual temperature value from the physical sensor
+ * @return true if support (coefficients none zero)
+ */
+void temperature_filter_get_temp(enum temp_sensor_id id, int *temp_ptr);
+
+/**
+ * Calculate the virtual temperature with the coefficients.
+ *
+ * @param id temp sensor id
+ * @param temp_ptr the actual temperature value from the physical sensor
+ * @return true if support (coefficients none zero)
+ */
+void temperature_filter_update_temp(enum temp_sensor_id id, int temp_ptr);
+
+#endif /* __CROS_EC_TEMPERATURE_FILTER_H */

zephyr/shim/src/CMakeLists.txt

@@ -79,7 +79,8 @@ zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_SWITCHCAP_GPIO
 zephyr_library_sources_ifdef(CONFIG_CROS_EC_SWITCHCAP_LN9310
 							    switchcap_ln9310.c)
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_TEMP_SENSOR temp_sensors.c
-                                                            thermal.c)
+                                                            thermal.c
+                                                            temperature_filter.c)
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_TIMER       hwtimer.c)
 zephyr_library_sources_ifdef(CONFIG_PLATFORM_EC_I2C         i2c.c)
 zephyr_library_sources_ifdef(CONFIG_SHIMMED_TASKS           tasks.c)

zephyr/shim/src/temp_sensors.c

@@ -23,6 +23,7 @@
 #include "temp_sensor/temp_sensor.h"
 #include "temp_sensor/thermistor.h"
 #include "temp_sensor/tmp112.h"
+#include "temperature_filter.h"
 
 #ifdef CONFIG_PLATFORM_EC_CUSTOMIZED_DESIGN
 #include "lotus/amd_r23m.h"
@@ -449,6 +450,7 @@ static bool temp_sensor_check_power(const struct temp_sensor_t *sensor)
 int temp_sensor_read(enum temp_sensor_id id, int *temp_ptr)
 {
 	const struct temp_sensor_t *sensor;
+	int rv = EC_SUCCESS;
 
 	if (id < 0 || id >= TEMP_SENSOR_COUNT)
 		return EC_ERROR_INVAL;
@@ -457,7 +459,12 @@ int temp_sensor_read(enum temp_sensor_id id, int *temp_ptr)
 	if (!temp_sensor_check_power(sensor))
 		return EC_ERROR_NOT_POWERED;
 
-	return sensor->zephyr_info->read(sensor, temp_ptr);
+	if (temperature_filter_is_support(id))
+		temperature_filter_get_temp(id, temp_ptr);
+	else
+		rv = sensor->zephyr_info->read(sensor, temp_ptr);
+
+	return rv;
 }
 
 void temp_sensors_update(void)
@@ -471,6 +478,18 @@ void temp_sensors_update(void)
 		if (!temp_sensor_check_power(sensor))
 			continue;
 
+		/**
+		 * thermal filter will use the one of physical sensor, so we don't
+		 * need to update the sensor again.
+		 */
+		if (temperature_filter_is_support(i)) {
+			int temp_ptr;
+
+			if (!sensor->zephyr_info->read(sensor, &temp_ptr))
+				temperature_filter_update_temp(i, temp_ptr);
+			continue;
+		}
+
 		sensor->zephyr_info->update_temperature(sensor->idx);
 	}
 }

zephyr/shim/src/temperature_filter.c

@@ -0,0 +1,92 @@
+/* Copyright 2025 The ChromiumOS Authors
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "hooks.h"
+#include "math_util.h"
+#include "temperature_filter.h"
+#include "thermal.h"
+#include "util.h"
+
+#define Q_SCALE 14
+/* scale input up to improve filter performance */
+#define IN_SCALE 7
+
+struct temperature_filter_t {
+	int32_t state[4];
+	int32_t coeff[6];
+} filters[TEMP_SENSOR_COUNT];
+
+static void temperature_filter_reset(enum temp_sensor_id id)
+{
+	memset(&filters[id].state, 30 << IN_SCALE, sizeof(filters[id].state));
+}
+
+static int temperature_filter_update(enum temp_sensor_id id, int value)
+{
+	/* we can only accept a range in INT8*/
+	value = MIN(value, INT8_MAX);
+	value = MAX(value, INT8_MIN);
+
+	int out_scaled =
+		filters[id].coeff[0] * (value << IN_SCALE) +
+		filters[id].coeff[1] * filters[id].state[0] +
+		filters[id].coeff[2] * filters[id].state[1] -
+		filters[id].coeff[4] * filters[id].state[2] -
+		filters[id].coeff[5] * filters[id].state[3];
+	int out = out_scaled >> Q_SCALE;
+	/* update delay line */
+	filters[id].state[1] = filters[id].state[0];
+	filters[id].state[3] = filters[id].state[2];
+	filters[id].state[0] = value << IN_SCALE;
+	filters[id].state[2] = out;
+
+	return out >> IN_SCALE;
+}
+
+static int temperature_filter_get(enum temp_sensor_id id)
+{
+	return filters[id].state[2] >> IN_SCALE;
+}
+
+bool temperature_filter_is_support(enum temp_sensor_id id)
+{
+	int zero[6] = {0};
+	int rv;
+
+	rv = memcmp(thermal_params[id].coefficients, zero, 6);
+
+	/* No coefficients (zero arrays), return false */
+	return !!rv;
+}
+
+void temperature_filter_get_temp(enum temp_sensor_id id, int *temp_ptr)
+{
+	*temp_ptr = C_TO_K(temperature_filter_get(id));
+}
+
+void temperature_filter_update_temp(enum temp_sensor_id id, int temp_ptr)
+{
+	/* The virtual temp is over range if we use the Kelvin */
+	temperature_filter_update(id, K_TO_C(temp_ptr));
+}
+
+static void temperature_filter_init(void)
+{
+	for (int temp_id = 0; temp_id < TEMP_SENSOR_COUNT; temp_id++) {
+		if (temperature_filter_is_support(temp_id))
+			memcpy(filters[temp_id].coeff, thermal_params[temp_id].coefficients,
+					sizeof(filters[temp_id].coeff));
+	}
+}
+DECLARE_HOOK(HOOK_INIT, temperature_filter_init, HOOK_PRIO_DEFAULT);
+
+static void temperature_filter_resume(void)
+{
+	for (int temp_id = 0; temp_id < TEMP_SENSOR_COUNT; temp_id++) {
+		if (temperature_filter_is_support(temp_id))
+			temperature_filter_reset(temp_id);
+	}
+}
+DECLARE_HOOK(HOOK_CHIPSET_RESUME, temperature_filter_resume, HOOK_PRIO_DEFAULT);

zephyr/shim/src/thermal.c

@@ -43,6 +43,7 @@
 		.temp_fan_max = C_TO_K(DT_PROP_OR(node_id,		\
 						  temp_fan_max,	\
 						  -273)),		\
+		.coefficients = DT_PROP_OR(node_id, coefficients, {0}), \
 	}
 
 struct ec_thermal_config thermal_params[] = {