[PATCH v4 1/5] hwmon: (aquacomputer_d5next) Avoid truncating scaled sensor readings

[Vas Zayarskiy <contact@vasily.cc>]

High Flow Next power is reported in watts. Multiplying the 16-bit value
by one million can overflow both the signed intermediate and the u32
cache. Store power in long, perform the conversion in u64, and clamp to
LONG_MAX. The other existing power conversions fit in a signed 32-bit
value. Return -ENODATA for unavailable power instead of exposing the
stored error as a reading.

Widen the shared current cache to u32. The Aquastream XT conversion to
milliamperes can exceed 65535 mA; clamp its negative conversion results
to zero before assigning to the unsigned cache. This also permits devices
with scaled aggregate currents to store milliamperes directly.

Assisted-by: LLM sparse
Signed-off-by: Vas Zayarskiy <contact@vasily.cc>
---
 drivers/hwmon/aquacomputer_d5next.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/aquacomputer_d5next.c b/drivers/hwmon/aquacomputer_d5next.c
index 1ca70e726..9178ac4cb 100644
--- a/drivers/hwmon/aquacomputer_d5next.c
+++ b/drivers/hwmon/aquacomputer_d5next.c
@@ -19,6 +19,7 @@
 #include <linux/hwmon.h>
 #include <linux/jiffies.h>
 #include <linux/ktime.h>
+#include <linux/limits.h>
 #include <linux/module.h>
 #include <linux/seq_file.h>
 #include <linux/unaligned.h>
@@ -599,9 +600,9 @@ struct aqc_data {
 	u32 speed_input_min[1];
 	u32 speed_input_target[1];
 	u32 speed_input_max[1];
-	u32 power_input[8];
+	long power_input[8];
 	u16 voltage_input[8];
-	u16 current_input[8];
+	u32 current_input[8];
 
 	/* Label values */
 	const char *const *temp_label;
@@ -976,7 +977,7 @@ static int aqc_legacy_read(struct aqc_data *priv)
 
 		/* Calculation derived from linear regression */
 		sensor_value = get_unaligned_le16(priv->buffer + AQUASTREAMXT_PUMP_CURR_OFFSET);
-		priv->current_input[0] = DIV_ROUND_CLOSEST(sensor_value * 176, 100) - 52;
+		priv->current_input[0] = max(DIV_ROUND_CLOSEST(sensor_value * 176, 100) - 52, 0);
 
 		sensor_value = get_unaligned_le16(priv->buffer + AQUASTREAMXT_PUMP_VOLTAGE_OFFSET);
 		priv->voltage_input[0] = DIV_ROUND_CLOSEST(sensor_value * 1000, 61);
@@ -1070,6 +1071,8 @@ static int aqc_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
 		}
 		break;
 	case hwmon_power:
+		if (priv->power_input[channel] == -ENODATA)
+			return -ENODATA;
 		*val = priv->power_input[channel];
 		break;
 	case hwmon_pwm:
@@ -1426,7 +1429,8 @@ static int aqc_raw_event(struct hid_device *hdev, struct hid_report *report, u8
 			priv->power_input[0] = -ENODATA;
 		else
 			priv->power_input[0] =
-			    get_unaligned_be16(data + HIGHFLOWNEXT_POWER) * 1000000;
+			    min_t(u64, get_unaligned_be16(data + HIGHFLOWNEXT_POWER) * 1000000ULL,
+				  LONG_MAX);
 
 		priv->voltage_input[0] = get_unaligned_be16(data + HIGHFLOWNEXT_5V_VOLTAGE) * 10;
 		priv->voltage_input[1] =