hwmon: (adm1177) fix sysfs ABI violation and current unit conversion

The adm1177 driver exposes the current alert threshold through
hwmon_curr_max_alarm. This violates the hwmon sysfs ABI, where
*_alarm attributes are read-only status flags and writable thresholds
must use currN_max.

The driver also stores the threshold internally in microamps, while
currN_max is defined in milliamps. Convert the threshold accordingly
on both the read and write paths.

Widen the cached threshold and related calculations to 64 bits so
that small shunt resistor values do not cause truncation or overflow.
Also use 64-bit arithmetic for the mA/uA conversions, clamp writes
to the range the hardware can represent, and propagate failures from
adm1177_write_alert_thr() instead of silently ignoring them.

Update the hwmon documentation to reflect the attribute rename and
the correct units returned by the driver.

Fixes: 09b08ac ("hwmon: (adm1177) Add ADM1177 Hot Swap Controller and Digital Power Monitor driver")
Signed-off-by: Sanman Pradhan <[email protected]>
Acked-by: Nuno Sá <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Guenter Roeck <[email protected]>

Author: Sanman Pradhan

Documentation/hwmon/adm1177.rst

@@ -27,10 +27,10 @@ for details.
 Sysfs entries
 -------------
 
-The following attributes are supported. Current maxim attribute
+The following attributes are supported. Current maximum attribute
 is read-write, all other attributes are read-only.
 
-in0_input		Measured voltage in microvolts.
+in0_input		Measured voltage in millivolts.
 
-curr1_input		Measured current in microamperes.
-curr1_max_alarm		Overcurrent alarm in microamperes.
+curr1_input		Measured current in milliamperes.
+curr1_max		Overcurrent shutdown threshold in milliamperes.

drivers/hwmon/adm1177.c

@@ -10,6 +10,8 @@
 #include <linux/hwmon.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
+#include <linux/math64.h>
+#include <linux/minmax.h>
 #include <linux/module.h>
 #include <linux/regulator/consumer.h>
 
@@ -33,7 +35,7 @@
 struct adm1177_state {
 	struct i2c_client	*client;
 	u32			r_sense_uohm;
-	u32			alert_threshold_ua;
+	u64			alert_threshold_ua;
 	bool			vrange_high;
 };
 
@@ -48,7 +50,7 @@ static int adm1177_write_cmd(struct adm1177_state *st, u8 cmd)
 }
 
 static int adm1177_write_alert_thr(struct adm1177_state *st,
-				   u32 alert_threshold_ua)
+				   u64 alert_threshold_ua)
 {
 	u64 val;
 	int ret;
@@ -91,8 +93,8 @@ static int adm1177_read(struct device *dev, enum hwmon_sensor_types type,
 			*val = div_u64((105840000ull * dummy),
 				       4096 * st->r_sense_uohm);
 			return 0;
-		case hwmon_curr_max_alarm:
-			*val = st->alert_threshold_ua;
+		case hwmon_curr_max:
+			*val = div_u64(st->alert_threshold_ua, 1000);
 			return 0;
 		default:
 			return -EOPNOTSUPP;
@@ -126,9 +128,10 @@ static int adm1177_write(struct device *dev, enum hwmon_sensor_types type,
 	switch (type) {
 	case hwmon_curr:
 		switch (attr) {
-		case hwmon_curr_max_alarm:
-			adm1177_write_alert_thr(st, val);
-			return 0;
+		case hwmon_curr_max:
+			val = clamp_val(val, 0,
+					div_u64(105840000ULL, st->r_sense_uohm));
+			return adm1177_write_alert_thr(st, (u64)val * 1000);
 		default:
 			return -EOPNOTSUPP;
 		}
@@ -156,7 +159,7 @@ static umode_t adm1177_is_visible(const void *data,
 			if (st->r_sense_uohm)
 				return 0444;
 			return 0;
-		case hwmon_curr_max_alarm:
+		case hwmon_curr_max:
 			if (st->r_sense_uohm)
 				return 0644;
 			return 0;
@@ -170,7 +173,7 @@ static umode_t adm1177_is_visible(const void *data,
 
 static const struct hwmon_channel_info * const adm1177_info[] = {
 	HWMON_CHANNEL_INFO(curr,
-			   HWMON_C_INPUT | HWMON_C_MAX_ALARM),
+			   HWMON_C_INPUT | HWMON_C_MAX),
 	HWMON_CHANNEL_INFO(in,
 			   HWMON_I_INPUT),
 	NULL
@@ -192,7 +195,8 @@ static int adm1177_probe(struct i2c_client *client)
 	struct device *dev = &client->dev;
 	struct device *hwmon_dev;
 	struct adm1177_state *st;
-	u32 alert_threshold_ua;
+	u64 alert_threshold_ua;
+	u32 prop;
 	int ret;
 
 	st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
@@ -208,22 +212,26 @@ static int adm1177_probe(struct i2c_client *client)
 	if (device_property_read_u32(dev, "shunt-resistor-micro-ohms",
 				     &st->r_sense_uohm))
 		st->r_sense_uohm = 0;
-	if (device_property_read_u32(dev, "adi,shutdown-threshold-microamp",
-				     &alert_threshold_ua)) {
-		if (st->r_sense_uohm)
-			/*
-			 * set maximum default value from datasheet based on
-			 * shunt-resistor
-			 */
-			alert_threshold_ua = div_u64(105840000000,
-						     st->r_sense_uohm);
-		else
-			alert_threshold_ua = 0;
+	if (!device_property_read_u32(dev, "adi,shutdown-threshold-microamp",
+				      &prop)) {
+		alert_threshold_ua = prop;
+	} else if (st->r_sense_uohm) {
+		/*
+		 * set maximum default value from datasheet based on
+		 * shunt-resistor
+		 */
+		alert_threshold_ua = div_u64(105840000000ULL,
+					     st->r_sense_uohm);
+	} else {
+		alert_threshold_ua = 0;
 	}
 	st->vrange_high = device_property_read_bool(dev,
 						    "adi,vrange-high-enable");
-	if (alert_threshold_ua && st->r_sense_uohm)
-		adm1177_write_alert_thr(st, alert_threshold_ua);
+	if (alert_threshold_ua && st->r_sense_uohm) {
+		ret = adm1177_write_alert_thr(st, alert_threshold_ua);
+		if (ret)
+			return ret;
+	}
 
 	ret = adm1177_write_cmd(st, ADM1177_CMD_V_CONT |
 				    ADM1177_CMD_I_CONT |