[PATCH v4 0/2] 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.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/hwmon/lm90.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/hwmon/lm90.c b/drivers/hwmon/lm90.c
index b53f17511b05..ee6b8190f08e 100644
--- a/drivers/hwmon/lm90.c
+++ b/drivers/hwmon/lm90.c

@@ -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.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
---
 drivers/hwmon/hwmon.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/drivers/hwmon/hwmon.c b/drivers/hwmon/hwmon.c
index fd47ab4e6892..9cb9d814cb88 100644
--- a/drivers/hwmon/hwmon.c
+++ b/drivers/hwmon/hwmon.c

@@ -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

On Tue, Jun 22, 2021 at 12:31:52AM +0300, Dmitry Osipenko wrote:

This and the adjustment below can be moved into the if() statement for lm99.
There is no need to affect other chips.

Please move this further below, just before val is used, to better
show the context why it is needed.

Thanks,
Guenter

 	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

On Tue, Jun 22, 2021 at 12:31:53AM +0300, Dmitry Osipenko wrote:

Please add
	if (!info[i])
		return 0;
here and drop the two checks for info[i] below.

Thanks,
Guenter

+	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