Support temperature trips by HWMON core and LM90 driver

Hi,

It's typical for embedded devices to use LM90-compatible sensor for monitoring of CPU core and skin temperatures. The sensor is often used by thermal zone that performs passive cooling and emergency shutdown on overheat, hence it's more optimal to use interrupt for a faster notification about temperature changes. Thermal framework provides set_trips() callback for programming of temperature trips, let's support it by HWMON.

Changelog:

v4: - Extended commit message of the set_trips() patch, saying that
it has no effect on sensors that can't set trips. This was suggested by Guenter Roeck.

- The channels are now iterated starting from 0 instead of 1 in the set_trips() callback. This was suggested by Guenter Roeck.

- Moved out declaration of the err variable into the upper scope of set_trips(), like it was suggested by Guenter Roeck. The checkpatch normally warns about missing empty line after a declaration, but it couldn't detect this case here.

- Replaced the err < 0 comparisons with err != 0, since write callback of the chip ops isn't supposed to return positive values. This was suggested by Guenter Roeck.

v3: - Improved patch that fixes integer overflows by fixing the hysteresis
underflow and improving the commit message, telling that min/max/crit fixes are only related to the LM99 sensor. Thanks to Guenter Roeck for the suggestion.

v2: - Reworked set_trips() by making it generic. Now callback invokes
the min/max temperature write method directly, instead of using additional new hwmon callback. This was suggested by Guenter Roeck.

- Added new patch that fixes integer overflows in the LM90 driver. The fixes are necessary for supporting set_trips().

Dmitry Osipenko (2):
hwmon: (lm90) Prevent integer underflows of temperature calculations
hwmon: Support set_trips() of thermal device ops

 drivers/hwmon/hwmon.c | 33 +++++++++++++++++++++++++++++++++
 drivers/hwmon/lm90.c  |  9 +++++++++
 2 files changed, 42 insertions(+)

2.30.2

The min/max/crit and all other temperature values that are passed to the driver are unlimited and value that is close to INT_MIN results in integer underflow of the temperature calculations made by the driver for LM99 sensor. Temperature hysteresis is among those values that need to be limited, but limiting of hysteresis is independent from the sensor version. Add the missing limits.

---
 drivers/hwmon/lm90.c | 9 +++++++++
 1 file changed, 9 insertions(+)

index b53f17511b05..ee6b8190f08e 100644
@@ -1028,6 +1028,9 @@ static int lm90_set_temp11(struct lm90_data *data, int index, long val)
 	struct reg *regp = &reg[index];
 	int err;
 
+	/* prevent integer underflow */
+	val = max(val, -128000l);
+
 	/* +16 degrees offset for temp2 for the LM99 */
 	if (data->kind == lm99 && index <= 2)
 		val -= 16000;

@@ -1088,6 +1091,9 @@ static int lm90_set_temp8(struct lm90_data *data, int index, long val)
 	struct i2c_client *client = data->client;
 	int err;
 
+	/* prevent integer underflow */
+	val = max(val, -128000l);
+
 	/* +16 degrees offset for temp2 for the LM99 */
 	if (data->kind == lm99 && index == 3)
 		val -= 16000;

@@ -1130,6 +1136,9 @@ static int lm90_set_temphyst(struct lm90_data *data, long val)
 	int temp;
 	int err;
 
+	/* prevent integer underflow */
+	val = max(val, -128000l);
+
 	if (data->kind == adt7461 || data->kind == tmp451)
 		temp = temp_from_u8_adt7461(data, data->temp8[LOCAL_CRIT]);
 	else if (data->kind == max6646)

2.30.2

Support set_trips() callback of thermal device ops. This allows HWMON device to operatively notify thermal core about temperature changes, which is very handy to have in a case where HWMON sensor is used by CPU thermal zone that performs passive cooling and emergency shutdown on overheat. Thermal core will be able to react faster to temperature changes.

The set_trips() callback is entirely optional. If HWMON sensor doesn't support setting thermal trips, then the callback is a NO-OP. The dummy callback has no effect on the thermal core. The temperature trips are either complement the temperature polling mechanism of thermal core or replace the polling if sensor can set the trips and polling is disabled by a particular device in a device-tree.

---
 drivers/hwmon/hwmon.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

index fd47ab4e6892..9cb9d814cb88 100644
@@ -153,8 +153,41 @@ static int hwmon_thermal_get_temp(void *data, int *temp)
 	return 0;
 }
 
+static int hwmon_thermal_set_trips(void *data, int low, int high)
+{
+	struct hwmon_thermal_data *tdata = data;
+	struct hwmon_device *hwdev = to_hwmon_device(tdata->dev);
+	const struct hwmon_chip_info *chip = hwdev->chip;
+	const struct hwmon_channel_info **info = chip->info;
+	unsigned int i;
+	int err;
+
+	if (!chip->ops->write)
+		return 0;
+
+	for (i = 0; info[i] && info[i]->type != hwmon_temp; i++)
+		continue;
+
+	if (info[i] && info[i]->config[tdata->index] & HWMON_T_MIN) {
+		err = chip->ops->write(tdata->dev, hwmon_temp,
+				       hwmon_temp_min, tdata->index, low);
+		if (err && err != -EOPNOTSUPP)
+			return err;
+	}
+
+	if (info[i] && info[i]->config[tdata->index] & HWMON_T_MAX) {
+		err = chip->ops->write(tdata->dev, hwmon_temp,
+				       hwmon_temp_max, tdata->index, high);
+		if (err && err != -EOPNOTSUPP)
+			return err;
+	}
+
+	return 0;
+}
+
 static const struct thermal_zone_of_device_ops hwmon_thermal_ops = {
 	.get_temp = hwmon_thermal_get_temp,
+	.set_trips = hwmon_thermal_set_trips,
 };
 
 static void hwmon_thermal_remove_sensor(void *data)

2.30.2