[1.] One line summary of the problem:
(regression) thermal zone - fan is turned on at higher temperature than it should
[2.] Full description of the problem/report:
After upgrade to 2.6.30-rc4 I noticed that my laptop's fan sometimes runs at lower speed than it used to.
2.6.29 does not have the bug.
The laptop (HP Compaq 6710b) has 5 ACPI cooling devices which correspond to different fan speeds. They are not turned on when I expect them to be.
Expected behavior:
Each active cooling device should be turned on when current temperature is equal or higher than its trip point.
(This is how it worked in 2.6.29 and earlier versions and also how it is defined by ACPI specification.)
Actual behavior in 2.6.30-rc4:
Each cooling device is turned on only when current temperature is strictly greater than the corresponding trip point but not when current temperature is equal to the trip point.
It is caused by commit b1569e99c795bf83b4ddf41c4f1c42761ab7f75e:
author Matthew Garrett <mjg59@xxxxxxxxxxxxx>
Wed, 3 Dec 2008 17:55:32 +0000 (17:55 +0000)
committer Len Brown <len.brown@xxxxxxxxx>
Fri, 20 Feb 2009 23:41:56 +0000 (18:41 -0500)
commit b1569e99c795bf83b4ddf41c4f1c42761ab7f75e
ACPI: move thermal trip handling to generic thermal layer
This commit (probably unintentionally) also changed how kernel determines if a cooling device has to be activated:
before the commit: cooling device is activated if current temperature >= trip point temperature
after the commit: cooling device is activated if current temperature > trip point temperature
I tried to change the trip point test back to "temp >= trip_temp" in drivers/thermal/termal_sys.c (attached patch). It fixes the issue on my laptop.
[3.] Keywords (i.e., modules, networking, kernel):
acpi, thermal zone
[4.] Kernel information
[4.1.] Kernel version (from /proc/version):
Linux version 2.6.30-rc4-64v01kms (root@V2G64) (gcc version 4.3.2 (Gentoo 4.3.2-r3 p1.6, pie-10.1.5) ) #2 SMP PREEMPT Fri May 1 00:11:41 CEST 2009
[5.] Most recent kernel version which did not have the bug:
2.6.29
[X.] Other notes, patches, fixes, workarounds:
patch which should fix the issue(for 2.6.30-rc4):
--- linux-2.6.30-rc4/drivers/thermal/thermal_sys.c 2009-04-30 23:52:59.000000000 +0200
+++ linux-2.6.30-rc4-p1/drivers/thermal/thermal_sys.c 2009-05-04 19:58:30.000000000 +0200
@@ -961,7 +961,7 @@ void thermal_zone_device_update(struct t
switch (trip_type) {
case THERMAL_TRIP_CRITICAL:
- if (temp > trip_temp) {
+ if (temp >= trip_temp) {
if (tz->ops->notify)
ret = tz->ops->notify(tz, count,
trip_type);
@@ -974,7 +974,7 @@ void thermal_zone_device_update(struct t
}
break;
case THERMAL_TRIP_HOT:
- if (temp > trip_temp)
+ if (temp >= trip_temp)
if (tz->ops->notify)
tz->ops->notify(tz, count, trip_type);
break;
@@ -986,14 +986,14 @@ void thermal_zone_device_update(struct t
cdev = instance->cdev;
- if (temp > trip_temp)
+ if (temp >= trip_temp)
cdev->ops->set_cur_state(cdev, 1);
else
cdev->ops->set_cur_state(cdev, 0);
}
break;
case THERMAL_TRIP_PASSIVE:
- if (temp > trip_temp || tz->passive)
+ if (temp >= trip_temp || tz->passive)
thermal_zone_device_passive(tz, temp,
trip_temp, count);
break;
--
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