[PATCH v3 1/1] hwmon: (asus-ec-sensors) detect unconnected physical sensors

[Eugene Shalygin <eugene.shalygin@gmail.com>]

When there is no physical sensor connected to the motherboard
socket,reading EC register returns one of the special values
(-62, -60, -40). Test for them  and return -ENODATA to hwmon.

Signed-off-by: Eugene Shalygin <eugene.shalygin@gmail.com>
---
 drivers/hwmon/asus-ec-sensors.c | 49 ++++++++++++++++++++++++++++++---
 1 file changed, 45 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/asus-ec-sensors.c b/drivers/hwmon/asus-ec-sensors.c
index 29a23484cbe7..3936006adeb6 100644
--- a/drivers/hwmon/asus-ec-sensors.c
+++ b/drivers/hwmon/asus-ec-sensors.c
@@ -185,6 +185,20 @@ enum ec_sensors {
 #define SENSOR_TEMP_SENSOR_EXTRA_2 BIT(ec_sensor_temp_sensor_extra_2)
 #define SENSOR_TEMP_SENSOR_EXTRA_3 BIT(ec_sensor_temp_sensor_extra_3)
 
+/*
+ * The values for temperature sensor readings without physical sensors connected.
+ * The value varies across generations and is seemingly defined by the EC chip
+ * used in the given board.
+ */
+static const s32 temperature_blank_values[] = {-62, -60, -40};
+
+static const s32 environment_temp_sensors =
+	SENSOR_TEMP_T_SENSOR | SENSOR_TEMP_T_SENSOR_ALT1 |
+	SENSOR_TEMP_WATER_IN | SENSOR_TEMP_WATER_OUT |
+	SENSOR_TEMP_WATER_BLOCK_IN | SENSOR_TEMP_WATER_BLOCK_OUT |
+	SENSOR_TEMP_T_SENSOR_2 | SENSOR_TEMP_SENSOR_EXTRA_1 |
+	SENSOR_TEMP_SENSOR_EXTRA_2 | SENSOR_TEMP_SENSOR_EXTRA_3;
+
 enum board_family {
 	family_unknown,
 	family_amd_400_series,
@@ -955,6 +969,7 @@ static const struct dmi_system_id dmi_table[] = {
 };
 
 struct ec_sensor {
+	/* this is ec_sensors enum value */
 	unsigned int info_index;
 	s32 cached_value;
 };
@@ -1047,6 +1062,12 @@ get_sensor_info(const struct ec_sensors_data *state, int index)
 	return state->sensors_info + state->sensors[index].info_index;
 }
 
+static enum ec_sensors
+get_ec_sensor_type(const struct ec_sensors_data *state, int index)
+{
+	return state->sensors[index].info_index;
+}
+
 static int find_ec_sensor_index(const struct ec_sensors_data *ec,
 				enum hwmon_sensor_types type, int channel)
 {
@@ -1291,6 +1312,17 @@ static int get_cached_value_or_update(const struct device *dev,
 	return 0;
 }
 
+static bool is_blank_temperature_value(s32 value)
+{
+	size_t i;
+
+	for (i = 0; i < ARRAY_SIZE(temperature_blank_values); ++i) {
+		if (value == temperature_blank_values[i])
+			return true;
+	}
+	return false;
+}
+
 /*
  * Now follow the functions that implement the hwmon interface
  */
@@ -1298,6 +1330,8 @@ static int get_cached_value_or_update(const struct device *dev,
 static int asus_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
 			      u32 attr, int channel, long *val)
 {
+	const struct ec_sensor_info *sensor_info;
+	enum ec_sensors ec_sensor;
 	int ret;
 	s32 value = 0;
 
@@ -1309,12 +1343,19 @@ static int asus_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
 	}
 
 	ret = get_cached_value_or_update(dev, sidx, state, &value);
-	if (!ret) {
-		*val = scale_sensor_value(value,
-					  get_sensor_info(state, sidx)->type);
+	if (ret)
+		return ret;
+
+	sensor_info = get_sensor_info(state, sidx);
+	if (sensor_info->type == hwmon_temp) {
+		ec_sensor = get_ec_sensor_type(state, sidx);
+		if ((environment_temp_sensors & BIT(ec_sensor)) &&
+		    is_blank_temperature_value(value))
+			return -ENODATA;
 	}
+	*val = scale_sensor_value(value, sensor_info->type);
 
-	return ret;
+	return 0;
 }
 
 static int asus_ec_hwmon_read_string(struct device *dev,
-- 
2.55.0