Support temperature trips by HWMON core and LM90 driver

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.

Signed-off-by Dmitry Osipenko <[email protected]>

---
 drivers/hwmon/hwmon.c | 12 ++++++++++++
 include/linux/hwmon.h |  9 +++++++++
 2 files changed, 21 insertions(+)

drivers/hwmon/hwmon.c +12 -0

index fd47ab4e6892..4bd39ed86877 100644
@@ -153,8 +153,20 @@ 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);
+
+	if (!hwdev->chip->ops->set_trips)
+		return 0;
+
+	return hwdev->chip->ops->set_trips(tdata->dev, tdata->index, low, high);
+}
+
 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)

include/linux/hwmon.h +9 -0

index 1e8d6ea8992e..7e5afcbf713d 100644
@@ -390,6 +390,14 @@ enum hwmon_intrusion_attributes {
  *			Channel number
  *		@val:	Value to write
  *		The function returns 0 on success or a negative error number.
+ * @set_trips:	Callback to set temperature trips. Optional.
+ *		Parameters are:
+ *		@dev:	Pointer to hardware monitoring device
+ *		@channel:
+ *			Channel number
+ *		@low:	Low temperature trip
+ *		@high:	High temperature trip
+ *		The function returns 0 on success or a negative error number.
  */
 struct hwmon_ops {
 	umode_t (*is_visible)(const void *drvdata, enum hwmon_sensor_types type,

@@ -400,6 +408,7 @@ struct hwmon_ops {
 		    u32 attr, int channel, const char **str);
 	int (*write)(struct device *dev, enum hwmon_sensor_types type,
 		     u32 attr, int channel, long val);
+	int (*set_trips)(struct device *dev, int channel, int low, int high);
 };
 
 /**

Signature · 1 line

2.30.2

Quoted 6 lines

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.

Why would this require a driver callback, and why can it not be handled in the hwmon core alone ? The hwmon core could register a set_trip function if the chip (driver) supports setting low and high limits, and it could call the appropriate driver functions when hwmon_thermal_set_trips() is called.

20.06.2021 20:23, Guenter Roeck пишет:

Quoted 8 lines · Dmitry Osipenko

Quoted 6 lines

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.

Quoted 5 lines

Why would this require a driver callback, and why can it not be handled in the hwmon core alone ? The hwmon core could register a set_trip function if the chip (driver) supports setting low and high limits, and it could call the appropriate driver functions when hwmon_thermal_set_trips() is called.

I wasn't sure about what other hwmon drivers may need and want to do for programming of the trips, so decided to start with this variant. I'll prepare v2 since you're suggesting that the universal callback should work okay for all drivers, thanks.

Quoted 15 lines

20.06.2021 20:23, Guenter Roeck пишет:

Quoted 8 lines · Dmitry Osipenko

Quoted 6 lines

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.

Quoted 5 lines

Why would this require a driver callback, and why can it not be handled in the hwmon core alone ? The hwmon core could register a set_trip function if the chip (driver) supports setting low and high limits, and it could call the appropriate driver functions when hwmon_thermal_set_trips() is called.

Quoted 4 lines

I wasn't sure about what other hwmon drivers may need and want to do for programming of the trips, so decided to start with this variant. I'll prepare v2 since you're suggesting that the universal callback should work okay for all drivers, thanks.

It will require some checks during probe to make sure that writeable limits exist, but that is still better than per-driver code. If for whatever reason some platform expects a different set of registers (say, critical limits instead of warning limits to attach to trip points), or if some platform expects that limits are _not_ used as trip points, that would not be driver but platform specific. You would not be able to address that on driver level with a single callback either (after all, lm90 compatible chips support up to three sets of limits).
That means you already made an implementation specific choice with your code, by selecting one of those three sets of limits to act as trip points, and by making trip point support mandatory for all lm90 compatible chips. If we need to make that configurable, we'll need a better solution than a single driver callback, and that solution may as well be generic and driver independent.