[PATCH v2 0/1] hwmon: (asus-ec-sensors) detect unconnected physical sensors

[PATCH v2 0/1] hwmon: (asus-ec-sensors) detect unconnected physical sensors

[Eugene Shalygin]

v2 changes: make temperature_blank_values array const.

Eugene Shalygin (1):
  hwmon: (asus-ec-sensors) detect unconnected physical sensors

 drivers/hwmon/asus-ec-sensors.c | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

-- 
2.55.0

[PATCH v2 1/1] hwmon: (asus-ec-sensors) detect unconnected physical sensors

[Eugene Shalygin]

When there is no temperature sensor connected, 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 | 27 +++++++++++++++++++++++++--
 1 file changed, 25 insertions(+), 2 deletions(-)

diff --git a/drivers/hwmon/asus-ec-sensors.c b/drivers/hwmon/asus-ec-sensors.c
index 29a23484cbe7..d805de5da7b2 100644
--- a/drivers/hwmon/asus-ec-sensors.c
+++ b/drivers/hwmon/asus-ec-sensors.c
@@ -67,6 +67,13 @@ static char *mutex_path_override;
 /* Moniker for the ACPI global lock (':' is not allowed in ASL identifiers) */
 #define ACPI_GLOBAL_LOCK_PSEUDO_PATH	":GLOBAL_LOCK"
 
+/*
+ * 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};
+
 typedef union {
 	u32 value;
 	struct {
@@ -1291,6 +1298,17 @@ 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 +1316,7 @@ 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;
 	int ret;
 	s32 value = 0;
 
@@ -1310,8 +1329,12 @@ 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);
+		sensor_info = get_sensor_info(state, sidx);
+		if (sensor_info->type == hwmon_temp &&
+		    is_blank_temperature_value(value)) {
+			return -ENODATA;
+		}
+		*val = scale_sensor_value(value, sensor_info->type);
 	}
 
 	return ret;
-- 
2.55.0

Re: [PATCH v2 1/1] hwmon: (asus-ec-sensors) detect unconnected physical sensors

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Blank temperature check applies to all thermal sensors, causing false `-ENODATA` errors during extreme subzero cooling.
--

--- Patch [1]: [PATCH v2 1/1] hwmon: (asus-ec-sensors) detect unconnected physical sensors ---
commit a1732d7627cd4596df1c72251d94e446dc0be771
Author: Eugene Shalygin <eugene.shalygin@gmail.com>

hwmon: (asus-ec-sensors) detect unconnected physical sensors

This commit adds a check for specific special values (-62, -60, -40)
returned by the EC when a temperature sensor is unconnected. When these
values are detected, the driver now returns -ENODATA instead of the raw
value to the hwmon subsystem.

> diff --git a/drivers/hwmon/asus-ec-sensors.c b/drivers/hwmon/asus-ec-sensors.c
> index 29a23484cbe7b..d805de5da7b24 100644
> --- a/drivers/hwmon/asus-ec-sensors.c
> +++ b/drivers/hwmon/asus-ec-sensors.c

[ ... ]

> @@ -1310,8 +1329,12 @@ 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);
> +		sensor_info = get_sensor_info(state, sidx);
> +		if (sensor_info->type == hwmon_temp &&
> +		    is_blank_temperature_value(value)) {
> +			return -ENODATA;
> +		}

[Severity: Medium]
Could this check inadvertently cause false read errors for legitimate subzero
temperatures?

Because this filter applies broadly to all hwmon_temp sensors in
asus_ec_hwmon_read(), it appears it would intercept valid extreme negative
temperatures, such as those seen during Liquid Nitrogen cooling setups. For
fixed onboard sensors like the CPU and VRM, values like -40, -60, or -62
might represent either genuine readings or the minimum clamped value of the
sensor's thermistor table.

Does this code risk disrupting monitoring tools and fan control daemons
during extreme subzero cooling by returning -ENODATA instead of the valid
clamped temperature?

> +		*val = scale_sensor_value(value, sensor_info->type);
>  	}
>  
>  	return ret;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260711101143.571191-2-eugene.shalygin@gmail.com?part=1