From 0dabe8a56f772f0ece46d2597799f412c277d874 Mon Sep 17 00:00:00 2001 From: Guenter Roeck Date: Tue, 4 Aug 2026 14:12:31 -0700 Subject: [PATCH] hwmon: (pmbus/lm25066) Fix PMBus coefficient calculations In lm25066_probe(), the PMBus coefficients for current and power are scaled based on the shunt resistor value. The calculation evaluates the multiplication using 32-bit arithmetic because info->m is an int and shunt is a u32: static int lm25066_probe(struct i2c_client *client) { ... info->m[PSC_CURRENT_IN] = info->m[PSC_CURRENT_IN] * shunt / 1000; info->m[PSC_POWER] = info->m[PSC_POWER] * shunt / 1000; ... } For large coefficients like 26882 (LM25056) or 15076 (LM5066i), a device tree shunt-resistor-micro-ohms value exceeding approximately 159,000 (159 mOhm, which is physically valid for low-current applications) causes the intermediate product to exceed UINT_MAX (4,294,967,295). This results in a silent wraparound before the division by 1000. Furthermore, if the wrapped value has the most significant bit set, converting it back to the signed int info->m results in negative coefficients. This logic error leads to drastically corrupted current and power readings, which can cause erratic thermal or power management behavior in the system. Fix the problem by using 64-bit operations for the multiply/divide operations. This can still overflow, but only for unreasonably large shunt resistor values. Reported-by: Sashiko Fixes: 94ee5fcc240fe ("hwmon: (pmbus/lm25066) Support configurable sense resistor values") Signed-off-by: Guenter Roeck --- drivers/hwmon/pmbus/lm25066.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/hwmon/pmbus/lm25066.c b/drivers/hwmon/pmbus/lm25066.c index 2be50cf1bbdea..c797e2e8258fd 100644 --- a/drivers/hwmon/pmbus/lm25066.c +++ b/drivers/hwmon/pmbus/lm25066.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include "pmbus.h" @@ -542,8 +543,8 @@ static int lm25066_probe(struct i2c_client *client) if (of_property_read_u32(client->dev.of_node, "shunt-resistor-micro-ohms", &shunt)) shunt = 1000; - info->m[PSC_CURRENT_IN] = info->m[PSC_CURRENT_IN] * shunt / 1000; - info->m[PSC_POWER] = info->m[PSC_POWER] * shunt / 1000; + info->m[PSC_CURRENT_IN] = DIV_ROUND_CLOSEST_ULL((u64)info->m[PSC_CURRENT_IN] * shunt, 1000); + info->m[PSC_POWER] = DIV_ROUND_CLOSEST_ULL((u64)info->m[PSC_POWER] * shunt, 1000); #if IS_ENABLED(CONFIG_SENSORS_LM25066_REGULATOR) /* LM25056 doesn't support OPERATION */ -- 2.47.3