Re: [RESEND PATCH v4 1/5] thermal: Add support for hardware-tracked trip points

From: Caesar Wang
Date: Fri Jun 03 2016 - 04:54:33 EST

Javi,

Thanks your comments.

On 2016å06æ03æ 01:30, Javi Merino wrote:
Hi Caesar,

On Fri, May 27, 2016 at 04:36:44PM +0800, Caesar Wang wrote:
From: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>

This adds support for hardware-tracked trip points to the device tree
thermal sensor framework.

The framework supports an arbitrary number of trip points. Whenever
the current temperature is updated, the trip points immediately
below and above the current temperature are found. A .set_trips
callback is then called with the temperatures. If there is no trip
point above or below the current temperature, the passed trip
temperature will be -INT_MAX or INT_MAX respectively. In this callback,
the driver should program the hardware such that it is notified
when either of these trip points are triggered. When a trip point
is triggered, the driver should call `thermal_zone_device_update'
for the respective thermal zone. This will cause the trip points
to be updated again.

If .set_trips is not implemented, the framework behaves as before.

This patch is based on an earlier version from Mikko Perttunen
<mikko.perttunen@xxxxxxxx>

Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
Signed-off-by: Caesar Wang <wxt@xxxxxxxxxxxxxx>
Cc: Zhang Rui <rui.zhang@xxxxxxxxx>
Cc: Eduardo Valentin <edubezval@xxxxxxxxx>
Cc: linux-pm@xxxxxxxxxxxxxxx

---

Changes in v4:
- Missing the lock added in v3.

Changes in v3:
- as Javi comments on https://patchwork.kernel.org/patch/9001281/.
- add the lock for preventing the called from multi placce
- add the note for pre_low/high_trip.

Changes in v2:
- update the sysfs-api.txt for set_trips.

Documentation/thermal/sysfs-api.txt | 7 +++++
drivers/thermal/thermal_core.c | 56 +++++++++++++++++++++++++++++++++++++
include/linux/thermal.h | 7 +++++
3 files changed, 70 insertions(+)

diff --git a/Documentation/thermal/sysfs-api.txt b/Documentation/thermal/sysfs-api.txt
index efc3f3d..75d8838 100644
--- a/Documentation/thermal/sysfs-api.txt
+++ b/Documentation/thermal/sysfs-api.txt
@@ -49,6 +49,9 @@ temperature) and throttle appropriate devices.
.bind: bind the thermal zone device with a thermal cooling device.
.unbind: unbind the thermal zone device with a thermal cooling device.
.get_temp: get the current temperature of the thermal zone.
+ .set_trips: set the trip points window. Whenever the current temperature
+ is updated, the trip points immediately below and above the
+ current temperature are found.
.get_mode: get the current mode (enabled/disabled) of the thermal zone.
- "enabled" means the kernel thermal management is enabled.
- "disabled" will prevent kernel thermal driver action upon trip points
@@ -95,6 +98,10 @@ temperature) and throttle appropriate devices.
get_temp: a pointer to a function that reads the
sensor temperature. This is mandatory
callback provided by sensor driver.
+ set_trips: a pointer to a function that sets a
+ temperature window. When this window is
+ left the driver must inform the thermal
+ core via thermal_zone_device_update.
get_trend: a pointer to a function that reads the
sensor temperature trend.
set_emul_temp: a pointer to a function that sets
diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
index 5133cd1..0591438 100644
--- a/drivers/thermal/thermal_core.c
+++ b/drivers/thermal/thermal_core.c
@@ -520,6 +520,55 @@ exit:
}
EXPORT_SYMBOL_GPL(thermal_zone_get_temp);
+static void thermal_zone_set_trips(struct thermal_zone_device *tz)
+{
+ int low = -INT_MAX;
+ int high = INT_MAX;
+ int trip_temp, hysteresis;
+ int temp = tz->temperature;
+ int i, ret;
+
+ if (!tz->ops->set_trips)
+ return;
+
+ for (i = 0; i < tz->trips; i++) {
+ int trip_low;
+
+ tz->ops->get_trip_temp(tz, i, &trip_temp);
+ tz->ops->get_trip_hyst(tz, i, &hysteresis);
+
+ trip_low = trip_temp - hysteresis;
You only use the hysteresis for the low trip point and not for the
high trip point. Shouldn't you also add:

trip_high = trip_temp + hysteresis;

...

I don't think so, I think we didn't need add the for trip_high.

We should triggle the trip points () in time when passive cooling,
and throttle the frequency with the related governor. (After all that's used for high temperature)
---

Maybe, we should think about the low temperature for thermal. (e.g. -10 degree, -20 degree....)
The rockchip some SoCs have the hardware low temperature interrupts for thermal,
but I haven't got up it.


+
+ if (trip_low < temp && trip_low > low)
+ low = trip_low;
+
+ if (trip_temp > temp && trip_temp < high)
+ high = trip_temp;
... and here:

if (trip_high > temp && trip_high < high)
high = trip_high;

Ditto

+ }
+
+ /* No need to change trip points */
+ if (tz->prev_low_trip == low && tz->prev_high_trip == high)
+ return;
+
+ mutex_lock(&tz->lock);
I think you should get the lock for the whole function, including the
read of tz->temperature . I know I said that the lock should be
acquired before the if condition before but thinking about it, I think
there may be a race condition if userspace updates the hysteresis
while thermal_zone_device_update() is updating the temperature: you
could have the cpu that is updating the hysteresis seeing the old
temperature while the cpu that is updating the temperature would see
the old hysteresis. I think it's safer if this whole function is
protected from the lock, from the read of tz->temperature until the
end.

Okay, I agree with you in here. :)
Thanks.

-
Caesar

Cheers,
Javi

+
+ tz->prev_low_trip = low;
+ tz->prev_high_trip = high;
+
+ dev_dbg(&tz->device, "new temperature boundaries: %d < x < %d\n",
+ low, high);
+
+ /*
+ * Set a temperature window. When this window is left the driver
+ * must inform the thermal core via thermal_zone_device_update.
+ */
+ ret = tz->ops->set_trips(tz, low, high);
+ if (ret)
+ dev_err(&tz->device, "Failed to set trips: %d\n", ret);
+
+ mutex_unlock(&tz->lock);
+}
+
static void update_temperature(struct thermal_zone_device *tz)
{
int temp, ret;
@@ -569,6 +618,8 @@ void thermal_zone_device_update(struct thermal_zone_device *tz)
update_temperature(tz);
+ thermal_zone_set_trips(tz);
+
for (count = 0; count < tz->trips; count++)
handle_thermal_trip(tz, count);
}
@@ -754,6 +805,9 @@ trip_point_hyst_store(struct device *dev, struct device_attribute *attr,
*/
ret = tz->ops->set_trip_hyst(tz, trip, temperature);
+ if (!ret)
+ thermal_zone_set_trips(tz);
+
return ret ? ret : count;
}
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--
caesar wang | software engineer | wxt@xxxxxxxxxxxxx