[PATCH 4/7] thermal: stats: introduce thermal zone stats/min_gradient

[Eduardo Valentin <evalenti@kernel.org>]

From: Eduardo Valentin <eduval@amazon.com>

The patch adds a statistic to track
the minimum gradient (dT/dt) to the thermal zone
stats/ folder.

Samples:

$ echo 1000 > emul_temp
$ cat stats/min_gradient
0
$ echo 2000 > emul_temp
$ echo 1000 > emul_temp
$ cat stats/min_gradient
-3460

Cc: "Rafael J. Wysocki" <rafael@kernel.org> (supporter:THERMAL)
Cc: Daniel Lezcano <daniel.lezcano@linaro.org> (supporter:THERMAL)
Cc: Amit Kucheria <amitk@kernel.org> (reviewer:THERMAL)
Cc: Zhang Rui <rui.zhang@intel.com> (reviewer:THERMAL)
Cc: Jonathan Corbet <corbet@lwn.net> (maintainer:DOCUMENTATION)
Cc: linux-pm@vger.kernel.org (open list:THERMAL)
Cc: linux-doc@vger.kernel.org (open list:DOCUMENTATION)
Cc: linux-kernel@vger.kernel.org (open list)

Signed-off-by: Eduardo Valentin <eduval@amazon.com>
---
 .../driver-api/thermal/sysfs-api.rst          |  1 +
 drivers/thermal/thermal_sysfs.c               | 23 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/Documentation/driver-api/thermal/sysfs-api.rst b/Documentation/driver-api/thermal/sysfs-api.rst
index 18140dbb1ce1..ed5e6ba4e0d7 100644
--- a/Documentation/driver-api/thermal/sysfs-api.rst
+++ b/Documentation/driver-api/thermal/sysfs-api.rst
@@ -358,6 +358,7 @@ Thermal zone device sys I/F, created once it's registered::
     |---stats:			Directory containing thermal zone device's stats
     |---stats/reset_tz_stats:	Writes to this file resets the statistics.
     |---stats/max_gradient:	The maximum recorded dT/dt in uC/ms.
+    |---stats/min_gradient:	The minimum recorded dT/dt in uC/ms.
 
 Thermal cooling device sys I/F, created once it's registered::
 
diff --git a/drivers/thermal/thermal_sysfs.c b/drivers/thermal/thermal_sysfs.c
index aa28c1cae916..f89ec9a7e8c8 100644
--- a/drivers/thermal/thermal_sysfs.c
+++ b/drivers/thermal/thermal_sysfs.c
@@ -542,6 +542,7 @@ static void destroy_trip_attrs(struct thermal_zone_device *tz)
 struct thermal_zone_device_stats {
 	spinlock_t lock; /* protects this struct */
 	s64 max_gradient;
+	s64 min_gradient;
 	ktime_t last_time;
 };
 
@@ -569,6 +570,10 @@ static void temperature_stats_update(struct thermal_zone_device *tz)
 	/* update fastest temperature rise from our perspective */
 	if (cur_gradient > stats->max_gradient)
 		stats->max_gradient = cur_gradient;
+
+	/* update fastest temperature decay from our perspective */
+	if (cur_gradient < stats->min_gradient)
+		stats->min_gradient = cur_gradient;
 }
 
 void thermal_zone_device_stats_update(struct thermal_zone_device *tz)
@@ -595,6 +600,21 @@ static ssize_t max_gradient_show(struct device *dev,
 	return ret;
 }
 
+static ssize_t min_gradient_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct thermal_zone_device *tz = to_thermal_zone(dev);
+	struct thermal_zone_device_stats *stats = tz->stats;
+	int ret;
+
+	spin_lock(&stats->lock);
+	temperature_stats_update(tz);
+	ret = snprintf(buf, PAGE_SIZE, "%lld\n", stats->min_gradient);
+	spin_unlock(&stats->lock);
+
+	return ret;
+}
+
 static ssize_t
 reset_tz_stats_store(struct device *dev, struct device_attribute *attr,
 		     const char *buf, size_t count)
@@ -604,6 +624,7 @@ reset_tz_stats_store(struct device *dev, struct device_attribute *attr,
 
 	spin_lock(&stats->lock);
 
+	stats->min_gradient = 0;
 	stats->max_gradient = 0;
 	stats->last_time = ktime_get();
 
@@ -612,10 +633,12 @@ reset_tz_stats_store(struct device *dev, struct device_attribute *attr,
 	return count;
 }
 
+static DEVICE_ATTR_RO(min_gradient);
 static DEVICE_ATTR_RO(max_gradient);
 static DEVICE_ATTR_WO(reset_tz_stats);
 
 static struct attribute *thermal_zone_device_stats_attrs[] = {
+	&dev_attr_min_gradient.attr,
 	&dev_attr_max_gradient.attr,
 	&dev_attr_reset_tz_stats.attr,
 	NULL
-- 
2.34.1