[PATCH] thermal: support forcing support for passive cooling

[Matthew Garrett <mjg59@srcf.ucam.org>]

Due to poor thermal design or Linux driving hardware outside its thermal 
envelope, some systems will reach critical temperature and shut down 
under high load. This patch adds support for forcing a polling-based 
passive trip point if the firmware doesn't provide one. The assumption 
is made that the processor is the most practical means to reduce the 
dynamic heat generation, so hitting the passive thermal limit will cause 
the CPU to be throttled until the temperature stabalises around the 
defined value.
    
UI is provided via a "passive" sysfs entry in the thermal zone 
directory. It accepts a decimal value in millidegrees celsius, or "0" to 
disable the functionality. Default behaviour is for this functionality 
to be disabled.
    
Signed-off-by: Matthew Garrett <mjg@redhat.com>
---

Depends on the code to move the trip handling into the generic layer. 
Tested this on a couple of machines and it seems to work well - a 
logical followup might be to allow the passive trip point to be 
overridden on machines that provide it.

 drivers/thermal/thermal_sys.c |   77 +++++++++++++++++++++++++++++++++++++++++
 include/linux/thermal.h       |    1 +
 2 files changed, 78 insertions(+), 0 deletions(-)

diff --git a/drivers/thermal/thermal_sys.c b/drivers/thermal/thermal_sys.c
index ac0f91f..c5351e5 100644
--- a/drivers/thermal/thermal_sys.c
+++ b/drivers/thermal/thermal_sys.c
@@ -214,9 +214,69 @@ trip_point_temp_show(struct device *dev, struct device_attribute *attr,
 	return sprintf(buf, "%ld\n", temperature);
 }
 
+static ssize_t
+passive_store(struct device *dev, struct device_attribute *attr,
+		    const char *buf, size_t count)
+{
+	struct thermal_zone_device *tz = to_thermal_zone(dev);
+	struct thermal_cooling_device *cdev = NULL;
+	int state;
+
+	if (!sscanf(buf, "%d\n", &state))
+		return -EINVAL;
+
+	if (state && !tz->forced_passive) {
+		mutex_lock(&thermal_list_lock);
+		list_for_each_entry(cdev, &thermal_cdev_list, node) {
+			if (!strncmp("Processor", cdev->type,
+				     sizeof("Processor")))
+				thermal_zone_bind_cooling_device(tz,
+								 THERMAL_TRIPS_NONE,
+								 cdev);
+		}
+		mutex_unlock(&thermal_list_lock);
+	} else if (!state && tz->forced_passive) {
+		mutex_lock(&thermal_list_lock);
+		list_for_each_entry(cdev, &thermal_cdev_list, node) {
+			if (!strncmp("Processor", cdev->type,
+				     sizeof("Processor")))
+				thermal_zone_unbind_cooling_device(tz,
+								   THERMAL_TRIPS_NONE,
+								   cdev);
+		}
+		mutex_unlock(&thermal_list_lock);
+	}
+
+	tz->tc1 = 1;
+	tz->tc2 = 1;
+
+	if (!tz->passive_delay)
+		tz->passive_delay = 1000;
+
+	if (!tz->polling_delay)
+		tz->polling_delay = 10000;
+
+	tz->forced_passive = state;
+
+	thermal_zone_device_update(tz);
+
+	return count;
+}
+
+static ssize_t
+passive_show(struct device *dev, struct device_attribute *attr,
+		   char *buf)
+{
+	struct thermal_zone_device *tz = to_thermal_zone(dev);
+
+	return sprintf(buf, "%d\n", tz->forced_passive);
+}
+
 static DEVICE_ATTR(type, 0444, type_show, NULL);
 static DEVICE_ATTR(temp, 0444, temp_show, NULL);
 static DEVICE_ATTR(mode, 0644, mode_show, mode_store);
+static DEVICE_ATTR(passive, S_IRUGO | S_IWUSR, passive_show, \
+		   passive_store);
 
 static struct device_attribute trip_point_attrs[] = {
 	__ATTR(trip_point_0_type, 0444, trip_point_type_show, NULL),
@@ -939,6 +999,11 @@ void thermal_zone_device_update(struct thermal_zone_device *tz)
 			break;
 		}
 	}
+
+	if (tz->forced_passive)
+		thermal_zone_device_passive(tz, temp, tz->forced_passive,
+					    THERMAL_TRIPS_NONE);
+
 	tz->last_temperature = temp;
 	if (tz->passive)
 		thermal_zone_device_set_polling(tz, tz->passive_delay);
@@ -977,8 +1042,10 @@ struct thermal_zone_device *thermal_zone_device_register(char *type,
 {
 	struct thermal_zone_device *tz;
 	struct thermal_cooling_device *pos;
+	enum thermal_trip_type trip_type;
 	int result;
 	int count;
+	int passive=0;
 
 	if (strlen(type) >= THERMAL_NAME_LENGTH)
 		return ERR_PTR(-EINVAL);
@@ -1041,8 +1108,18 @@ struct thermal_zone_device *thermal_zone_device_register(char *type,
 		TRIP_POINT_ATTR_ADD(&tz->device, count, result);
 		if (result)
 			goto unregister;
+		tz->ops->get_trip_type(tz, count, &trip_type);
+		if (trip_type == THERMAL_TRIP_PASSIVE)
+			passive=1;
 	}
 
+	if (!passive)
+		result = device_create_file(&tz->device,
+					    &dev_attr_passive);
+
+	if (result)
+		goto unregister;
+
 	result = thermal_add_hwmon_sysfs(tz);
 	if (result)
 		goto unregister;
diff --git a/include/linux/thermal.h b/include/linux/thermal.h
index a81c615..1de8b9e 100644
--- a/include/linux/thermal.h
+++ b/include/linux/thermal.h
@@ -113,6 +113,7 @@ struct thermal_zone_device {
 	int polling_delay;
 	int last_temperature;
 	bool passive;
+	unsigned int forced_passive;
 	struct thermal_zone_device_ops *ops;
 	struct list_head cooling_devices;
 	struct idr idr;

-- 
Matthew Garrett | mjg59@srcf.ucam.org