ACPI Thermal workaround hooks

In response to the outcry after I deleted the trip-point overrides, here is how I think we can work-around thermal issues in a supportable way.

In particular, this series should address the issues on Knut's AOpen Award system here:
http://bugzilla.kernel.org/show_bug.cgi?id=8842
and give us the hooks to address analogous issues in other systems.

Please let me know what you think.

thanks,
-Len

In response to the outcry after I deleted the trip-point overrides, here is how I think we can work-around thermal issues in a supportable way.

In particular, this series should address the issues on Knut's AOpen Award system here:
http://bugzilla.kernel.org/show_bug.cgi?id=8842
and give us the hooks to address analogous issues in other systems.

Please let me know what you think.

thanks,
-Len

"thermal.off=1" disables all ACPI thermal support at boot time, just as CONFIG_ACPI_THERMAL=n does at build time.

This bootparam is for users who run pre-compiled kernels, but have some intractable issue with ACPI thermal control.

Note that on some systems, disabling ACPI thermal support will cause the system to run hotter and reduce the lifetime of the hardware.

---
 Documentation/kernel-parameters.txt |    3 +++
 drivers/acpi/thermal.c              |    9 ++++++++-
 2 files changed, 11 insertions(+), 1 deletions(-)

index efdb42f..464aea1 100644
@@ -1820,6 +1820,9 @@ and is between 256 and 4096 characters. It is defined in the file
 	thash_entries=	[KNL,NET]
 			Set number of hash buckets for TCP connection
 
+	thermal.off=	[HW,ACPI]
+			1: disable ACPI thermal control
+
 	time		Show timing data prefixed to each printk message line
 			[deprecated, see 'printk.time']
 

index 5a62de1..61337d9 100644
@@ -78,6 +78,10 @@ static int tzp;
 module_param(tzp, int, 0);
 MODULE_PARM_DESC(tzp, "Thermal zone polling frequency, in 1/10 seconds.\n");
 
+static int off;
+module_param(off, int, 0);
+MODULE_PARM_DESC(off, "Set to disable ACPI thermal support.\n");
+
 static int acpi_thermal_add(struct acpi_device *device);
 static int acpi_thermal_remove(struct acpi_device *device, int type);
 static int acpi_thermal_resume(struct acpi_device *device);

@@ -1285,7 +1289,10 @@ static int __init acpi_thermal_init(void)
 {
 	int result = 0;
 
-
+	if (off) {
+		printk(KERN_NOTICE "ACPI: thermal control disabled\n");
+		return -ENODEV;
+	}
 	acpi_thermal_dir = proc_mkdir(ACPI_THERMAL_CLASS, acpi_root_dir);
 	if (!acpi_thermal_dir)
 		return -ENODEV;

1.5.3.rc4.29.g74276

Thermal Zone Polling frequency (_TZP) is an optional ACPI object recommending the rate that the OS should poll the associated thermal zone.

If _TZP is 0, no polling should be used.
If _TZP is non-zero, then the platform recommends that the thermal zone be polled at the specified rate. The minimum period is 30 seconds.
The maximum period is 5 minutes.

(note _TZP and thermal.tzp units are in deci-seconds,
so _TZP = 300 corresponds to 30 seconds)

If _TZP is not present, ACPI 3.0b recommends that the thermal zone be polled at an "OS provided default frequency".

However, common industry practice is:
1. The BIOS never specifies any _TZP
2. The OS never polls any thermal zones

Ie. OS depends on the platform's ability to
provoke thermal events when necessary, and
the "OS provided default frequency" is "never":-)

The Linux kernel already follows this common industry practice -- thermal zones are not polled unless _TZP is present and non-zero.

But thermal zone polling is useful as a workaround for systems which have ACPI thermal control, but have an issue with thermal events. Indeed, some Linux distributions still set a non-zero thermal polling frequency for this reason.

But rather than ask the user to write a polling frequency into all the /proc/acpi/thermal_zone/*/polling_frequency files, here we simply document and expose the already existing module parameter to do the same at system level.

Note this is a module-load time parameter only.

---
 Documentation/kernel-parameters.txt |    5 +++++
 drivers/acpi/thermal.c              |    2 +-
 2 files changed, 6 insertions(+), 1 deletions(-)

index 464aea1..2c21ed4 100644
@@ -1823,6 +1823,11 @@ and is between 256 and 4096 characters. It is defined in the file
 	thermal.off=	[HW,ACPI]
 			1: disable ACPI thermal control
 
+	thermal.tzp=	[HW,ACPI]
+			Specify global default ACPI thermal zone polling rate
+			<deci-seconds>: poll all this frequency
+			0: no polling (default)
+
 	time		Show timing data prefixed to each printk message line
 			[deprecated, see 'printk.time']
 

index 61337d9..b6b3bec 100644
@@ -75,7 +75,7 @@ MODULE_DESCRIPTION("ACPI Thermal Zone Driver");
 MODULE_LICENSE("GPL");
 
 static int tzp;
-module_param(tzp, int, 0);
+module_param(tzp, int, 0444);
 MODULE_PARM_DESC(tzp, "Thermal zone polling frequency, in 1/10 seconds.\n");
 
 static int off;

1.5.3.rc4.29.g74276

"thermal.psv=0" disables passive trip points for all ACPI thermal zones.

"thermal.psv=C", where 'C' is degrees Celcius, overrides existing passive trip points
for all ACPI thermal zones.

thermal.psv is checked at module load time, and in response to trip-point change events.

Note that if the system does not deliver thermal zone temperature change events near the new trip-point, then it will not be noticed. To force it to be noticed, you can enable polling:
eg. thermal.tzp=3000 invokes polling every 5 minutes.

Note that once passive thermal throttling is invoked, it has its own internal polling frequencey that is independent of tzp.

WARNING: disabling or raising a thermal trip point will result in increased running temperature and shorter hardware lifetime on some systems.

---
 Documentation/kernel-parameters.txt |    4 ++++
 drivers/acpi/thermal.c              |   17 ++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

index 2c21ed4..9118fc6 100644
@@ -1823,6 +1823,10 @@ and is between 256 and 4096 characters. It is defined in the file
 	thermal.off=	[HW,ACPI]
 			1: disable ACPI thermal control
 
+	thermal.psv=	[HW,ACPI]
+			0: disable all passive trip points
+			<degrees C>: override all passive trip points to this value
+
 	thermal.tzp=	[HW,ACPI]
 			Specify global default ACPI thermal zone polling rate
 			<deci-seconds>: poll all this frequency

index b6b3bec..9d7453c 100644
@@ -82,6 +82,10 @@ static int off;
 module_param(off, int, 0);
 MODULE_PARM_DESC(off, "Set to disable ACPI thermal support.\n");
 
+static int psv = -1;
+module_param(psv, int, 0644);
+MODULE_PARM_DESC(psv, "Disable or override all passive trip points.\n");
+
 static int acpi_thermal_add(struct acpi_device *device);
 static int acpi_thermal_remove(struct acpi_device *device, int type);
 static int acpi_thermal_resume(struct acpi_device *device);

@@ -343,9 +347,16 @@ static int acpi_thermal_get_trip_points(struct acpi_thermal *tz)
 
 	/* Passive: Processors (optional) */
 
-	status =
-	    acpi_evaluate_integer(tz->device->handle, "_PSV", NULL,
-				  &tz->trips.passive.temperature);
+	if (psv == 0) {
+		status = AE_SUPPORT;
+	} else if (psv > 0) {
+		tz->trips.passive.temperature = psv;
+		status = AE_OK;
+	} else {
+		status = acpi_evaluate_integer(tz->device->handle,
+			"_PSV", NULL, &tz->trips.passive.temperature);
+	}
+
 	if (ACPI_FAILURE(status)) {
 		tz->trips.passive.flags.valid = 0;
 		ACPI_DEBUG_PRINT((ACPI_DB_INFO, "No passive threshold\n"));

1.5.3.rc4.29.g74276

thermal.nocrt=1 disables actions on _CRT and _HOT ACPI thermal zone trip-points. They will be marked as <disabled> in /proc/acpi/thermal_zone/*/trip_points.

There are two cases where this option is used:

1. Debugging a hot system crossing valid trip point.

If your system fan is spinning at full speed,
be sure that the vent is not clogged with dust.
Many laptops have very fine thermal fins that are easily blocked.

Check that the processor fan-sink is properly seated, has the proper thermal grease, and is really spinning.

Check for fan related options in BIOS SETUP. Sometimes there is a performance vs quiet option. Defaults are generally the most conservative.

If your fan is not spinning, yet /proc/acpi/fan/ has files in it, please file a Linux/ACPI bug.

WARNING: you risk shortening the lifetime of your hardware if you use this parameter on a hot system. Note that this refers to all system components, including the disk drive.

2. Working around a cool system crossing critical trip point due to erroneous temperature reading.

Try again with CONFIG_HWMON=n
There is known potential for conflict between the the hwmon sub-system and the ACPI BIOS.
If this fixes it, notify [email protected] and [email protected]

Otherwise, file a Linux/ACPI bug, or notify
just [email protected].

---
 Documentation/kernel-parameters.txt |    4 ++++
 drivers/acpi/thermal.c              |   18 ++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)

index 9118fc6..897bb63 100644
@@ -1820,6 +1820,10 @@ and is between 256 and 4096 characters. It is defined in the file
 	thash_entries=	[KNL,NET]
 			Set number of hash buckets for TCP connection
 
+	thermal.nocrt=	[HW,ACPI]
+			Set to disable actions on ACPI thermal zone
+			critical and hot trip points.
+
 	thermal.off=	[HW,ACPI]
 			1: disable ACPI thermal control
 

index 9d7453c..1642980 100644
@@ -78,6 +78,10 @@ static int tzp;
 module_param(tzp, int, 0444);
 MODULE_PARM_DESC(tzp, "Thermal zone polling frequency, in 1/10 seconds.\n");
 
+static int nocrt;
+module_param(nocrt, int, 0);
+MODULE_PARM_DESC(nocrt, "Set to disable action on ACPI thermal zone critical and hot trips.\n");
+
 static int off;
 module_param(off, int, 0);
 MODULE_PARM_DESC(off, "Set to disable ACPI thermal support.\n");

@@ -442,7 +446,7 @@ static int acpi_thermal_get_devices(struct acpi_thermal *tz)
 
 static int acpi_thermal_critical(struct acpi_thermal *tz)
 {
-	if (!tz || !tz->trips.critical.flags.valid)
+	if (!tz || !tz->trips.critical.flags.valid || nocrt)
 		return -EINVAL;
 
 	if (tz->temperature >= tz->trips.critical.temperature) {

@@ -464,7 +468,7 @@ static int acpi_thermal_critical(struct acpi_thermal *tz)
 
 static int acpi_thermal_hot(struct acpi_thermal *tz)
 {
-	if (!tz || !tz->trips.hot.flags.valid)
+	if (!tz || !tz->trips.hot.flags.valid || nocrt)
 		return -EINVAL;
 
 	if (tz->temperature >= tz->trips.hot.temperature) {

@@ -839,12 +843,14 @@ static int acpi_thermal_trip_seq_show(struct seq_file *seq, void *offset)
 		goto end;
 
 	if (tz->trips.critical.flags.valid)
-		seq_printf(seq, "critical (S5):           %ld C\n",
-			   KELVIN_TO_CELSIUS(tz->trips.critical.temperature));
+		seq_printf(seq, "critical (S5):           %ld C%s",
+			   KELVIN_TO_CELSIUS(tz->trips.critical.temperature),
+			   nocrt ? " <disabled>\n" : "\n");
 
 	if (tz->trips.hot.flags.valid)
-		seq_printf(seq, "hot (S4):                %ld C\n",
-			   KELVIN_TO_CELSIUS(tz->trips.hot.temperature));
+		seq_printf(seq, "hot (S4):                %ld C%s",
+			   KELVIN_TO_CELSIUS(tz->trips.hot.temperature),
+			   nocrt ? " <disabled>\n" : "\n");
 
 	if (tz->trips.passive.flags.valid) {
 		seq_printf(seq,

1.5.3.rc4.29.g74276

thermal.act=-1 disables all active trip points
in all ACPI thermal zones.

thermal.act=C, where C > 0, overrides all first active trip points in all thermal zones to C degrees Celcius.

Note, overriding this trip-point will disable any BIOS attempts to implement hysterisis around AC0, and may result in the fan starting and stopping frequently if temperature frequently crosses C.

---
 Documentation/kernel-parameters.txt |    4 ++++
 drivers/acpi/thermal.c              |   20 ++++++++++++++++----
 2 files changed, 20 insertions(+), 4 deletions(-)

index 897bb63..a82d46f 100644
@@ -1820,6 +1820,10 @@ and is between 256 and 4096 characters. It is defined in the file
 	thash_entries=	[KNL,NET]
 			Set number of hash buckets for TCP connection
 
+	thermal.act=	[HW,ACPI]
+			-1: disable all active trip points in all thermal zones
+			<degrees C>: override all lowest active trip points
+
 	thermal.nocrt=	[HW,ACPI]
 			Set to disable actions on ACPI thermal zone
 			critical and hot trip points.

index 1642980..2b48ab9 100644
@@ -74,6 +74,10 @@ MODULE_AUTHOR("Paul Diefenbaugh");
 MODULE_DESCRIPTION("ACPI Thermal Zone Driver");
 MODULE_LICENSE("GPL");
 
+static int act;
+module_param(act, int, 0644);
+MODULE_PARM_DESC(act, "Disable or override all lowest active trip points.\n");
+
 static int tzp;
 module_param(tzp, int, 0444);
 MODULE_PARM_DESC(tzp, "Thermal zone polling frequency, in 1/10 seconds.\n");

@@ -405,11 +409,19 @@ static int acpi_thermal_get_trip_points(struct acpi_thermal *tz)
 
 		char name[5] = { '_', 'A', 'C', ('0' + i), '\0' };
 
-		status =
-		    acpi_evaluate_integer(tz->device->handle, name, NULL,
-					  &tz->trips.active[i].temperature);
-		if (ACPI_FAILURE(status))
+		if (act == -1)
+			break;	/* disable all active trip points */
+
+		status = acpi_evaluate_integer(tz->device->handle,
+			name, NULL, &tz->trips.active[i].temperature);
+
+		if (ACPI_FAILURE(status)) {
+			/* override last valid trip point */
+			if ((i > 0) && (act > 0))
+				tz->trips.active[i - 1].temperature =
+					CELSIUS_TO_KELVIN(act);
 			break;
+		}
 
 		name[2] = 'L';
 		status =

1.5.3.rc4.29.g74276

Use DMI to:
1. enable polling (BIOS thermal events are broken)
2. disable active trip points (BIOS fan control is broken)
3. disable passive trip point (BIOS hard-codes it too low)

The actual temperature reading does work,
and with the aid of polling, the critical
trip point should work too.

http://bugzilla.kernel.org/show_bug.cgi?id=8842

---
 drivers/acpi/thermal.c |   65 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 65 insertions(+), 0 deletions(-)

index 2b48ab9..d105d65 100644
@@ -33,6 +33,7 @@
 
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/dmi.h>
 #include <linux/init.h>
 #include <linux/types.h>
 #include <linux/proc_fs.h>

@@ -1314,10 +1315,74 @@ static int acpi_thermal_resume(struct acpi_device *device)
 	return AE_OK;
 }
 
+#ifdef CONFIG_DMI
+static int thermal_act(struct dmi_system_id *d) {
+
+	if (act == 0) {
+		printk(KERN_NOTICE "ACPI: %s detected: "
+			"disabling all active thermal trip points\n", d->ident);
+		act = -1;
+	}
+	return 0;
+}
+static int thermal_tzp(struct dmi_system_id *d) {
+
+	if (tzp == 0) {
+		printk(KERN_NOTICE "ACPI: %s detected: "
+			"enabling thermal zone polling\n", d->ident);
+		tzp = 300;	/* 300 dS = 30 Seconds */
+	}
+	return 0;
+}
+static int thermal_psv(struct dmi_system_id *d) {
+
+	if (psv == 0) {
+		printk(KERN_NOTICE "ACPI: %s detected: "
+			"disabling all passive thermal trip points\n", d->ident);
+		psv = -1;
+	}
+	return 0;
+}
+
+static struct dmi_system_id thermal_dmi_table[] __initdata = {
+	/*
+	 * Award BIOS on this AOpen makes thermal control almost worthless.
+	 * http://bugzilla.kernel.org/show_bug.cgi?id=8842
+	 */
+	{
+	 .callback = thermal_act,
+	 .ident = "AOpen i915GMm-HFS",
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "AOpen"),
+		DMI_MATCH(DMI_BOARD_NAME, "i915GMm-HFS"),
+		},
+	},
+	{
+	 .callback = thermal_psv,
+	 .ident = "AOpen i915GMm-HFS",
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "AOpen"),
+		DMI_MATCH(DMI_BOARD_NAME, "i915GMm-HFS"),
+		},
+	},
+	{
+	 .callback = thermal_tzp,
+	 .ident = "AOpen i915GMm-HFS",
+	 .matches = {
+		DMI_MATCH(DMI_BOARD_VENDOR, "AOpen"),
+		DMI_MATCH(DMI_BOARD_NAME, "i915GMm-HFS"),
+		},
+	},
+	{}
+};
+#endif /* CONFIG_DMI */
+
 static int __init acpi_thermal_init(void)
 {
 	int result = 0;
 
+	dmi_check_system(thermal_dmi_table);
+
 	if (off) {
 		printk(KERN_NOTICE "ACPI: thermal control disabled\n");
 		return -ENODEV;

1.5.3.rc4.29.g74276

Subject: ACPI: thermal: create "thermal.act=" to disable or override active trip point

From: Len Brown <[email protected]>

thermal.act=-1 disables all active trip points
in all ACPI thermal zones.

thermal.act=C, where C > 0, overrides all lowest temperature active trip points in all thermal zones to C degrees Celsius. Raising this trip-point may allow you to keep your system silent up to a higher temperature. However, it will not allow you to raise the lowest temperature trip point above the next higher trip point (if there is one). Lowering this trip point may kick in the fan sooner.

Note that overriding this trip-point will disable any BIOS attempts to implement hysteresis around the lowest temperature trip point. This may result in the fan starting and stopping frequently if temperature frequently crosses C.

WARNING: raising trip points above the manufacturer's defaults may cause the system to run at higher temperature and shorten its life.

---

refreshed to add check to limit trip-point override to equal the next higher trip point.

Index: linus/Documentation/kernel-parameters.txt
===================================================================
@@ -1820,6 +1820,10 @@ and is between 256 and 4096 characters. 
 	thash_entries=	[KNL,NET]
 			Set number of hash buckets for TCP connection
 
+	thermal.act=	[HW,ACPI]
+			-1: disable all active trip points in all thermal zones
+			<degrees C>: override all lowest active trip points
+
 	thermal.nocrt=	[HW,ACPI]
 			Set to disable actions on ACPI thermal zone
 			critical and hot trip points.

Index: linus/drivers/acpi/thermal.c
===================================================================
@@ -74,6 +74,10 @@ MODULE_AUTHOR("Paul Diefenbaugh");
 MODULE_DESCRIPTION("ACPI Thermal Zone Driver");
 MODULE_LICENSE("GPL");
 
+static int act;
+module_param(act, int, 0644);
+MODULE_PARM_DESC(act, "Disable or override all lowest active trip points.\n");
+
 static int tzp;
 module_param(tzp, int, 0444);
 MODULE_PARM_DESC(tzp, "Thermal zone polling frequency, in 1/10 seconds.\n");

@@ -405,11 +409,33 @@ static int acpi_thermal_get_trip_points(
 
 		char name[5] = { '_', 'A', 'C', ('0' + i), '\0' };
 
-		status =
-		    acpi_evaluate_integer(tz->device->handle, name, NULL,
-					  &tz->trips.active[i].temperature);
-		if (ACPI_FAILURE(status))
+		if (act == -1)
+			break;	/* disable all active trip points */
+
+		status = acpi_evaluate_integer(tz->device->handle,
+			name, NULL, &tz->trips.active[i].temperature);
+
+		if (ACPI_FAILURE(status)) {
+			if (i == 0)	/* no active trip points */
+				break;
+			if (act <= 0)	/* no override requested */
+				break;
+			if (i == 1) {	/* 1 trip point */
+				tz->trips.active[0].temperature =
+					CELSIUS_TO_KELVIN(act);
+			} else {	/* multiple trips */
+				/*
+				 * Don't allow override higher than
+				 * the next higher trip point
+				 */
+				tz->trips.active[i - 1].temperature =
+				    (tz->trips.active[i - 2].temperature <
+					CELSIUS_TO_KELVIN(act) ?
+					tz->trips.active[i - 2].temperature :
+					CELSIUS_TO_KELVIN(act));
+			}
 			break;
+		}
 
 		name[2] = 'L';
 		status =

Subject: ACPI: thermal: create "thermal.psv=" to override passive trip points

From: Len Brown <[email protected]>

"thermal.psv=-1" disables passive trip points for all ACPI thermal zones.

"thermal.psv=C", where 'C' is degrees Celsius, overrides all existing passive trip points for all ACPI thermal zones.

thermal.psv is checked at module load time, and in response to trip-point change events.

Note that if the system does not deliver thermal zone temperature change events near the new trip-point, then it will not be noticed. To force your custom trip point to be noticed, you may need to enable polling:
eg. thermal.tzp=3000 invokes polling every 5 minutes.

Note that once passive thermal throttling is invoked, it has its own internal Thermal Sampling Period (_TSP), that is unrelated to _TZP.

WARNING: disabling or raising a thermal trip point may result in increased running temperature and shorter hardware lifetime on some systems.

---

This updates the previous version of this patch so that -1 disables _PSV (instead of 0), and the user's Celsius value is properly converted to Kelvin*10 for internal use.

Index: linus/Documentation/kernel-parameters.txt
===================================================================
@@ -1823,6 +1823,10 @@ and is between 256 and 4096 characters. 
 	thermal.off=	[HW,ACPI]
 			1: disable ACPI thermal control
 
+	thermal.psv=	[HW,ACPI]
+			-1: disable all passive trip points
+			<degrees C>: override all passive trip points to this value
+
 	thermal.tzp=	[HW,ACPI]
 			Specify global default ACPI thermal zone polling rate
 			<deci-seconds>: poll all this frequency

Index: linus/drivers/acpi/thermal.c
===================================================================
@@ -82,6 +82,10 @@ static int off;
 module_param(off, int, 0);
 MODULE_PARM_DESC(off, "Set to disable ACPI thermal support.\n");
 
+static int psv;
+module_param(psv, int, 0644);
+MODULE_PARM_DESC(psv, "Disable or override all passive trip points.\n");
+
 static int acpi_thermal_add(struct acpi_device *device);
 static int acpi_thermal_remove(struct acpi_device *device, int type);
 static int acpi_thermal_resume(struct acpi_device *device);

@@ -343,9 +347,16 @@ static int acpi_thermal_get_trip_points(
 
 	/* Passive: Processors (optional) */
 
-	status =
-	    acpi_evaluate_integer(tz->device->handle, "_PSV", NULL,
-				  &tz->trips.passive.temperature);
+	if (psv == -1) {
+		status = AE_SUPPORT;
+	} else if (psv > 0) {
+		tz->trips.passive.temperature = CELSIUS_TO_KELVIN(psv);
+		status = AE_OK;
+	} else {
+		status = acpi_evaluate_integer(tz->device->handle,
+			"_PSV", NULL, &tz->trips.passive.temperature);
+	}
+
 	if (ACPI_FAILURE(status)) {
 		tz->trips.passive.flags.valid = 0;
 		ACPI_DEBUG_PRINT((ACPI_DB_INFO, "No passive threshold\n"));

Thanks.
This is very much appreciated.

I like the idea of boot parameters, this avoids the seduction to build tools on it and mis-use this as an official interface.

But where I like to see a sysfs interface for, is the passive trip point and allow:
a) lowering passive trip points
b) let user define his own passive trip point if none
is provided by BIOS

I don't remember whether every trip point gets it's own sysfs file. If yes, adding a passive_user file, default -1 and the normal passive file where the current active passive trip point value is shown, is how I think this could be done.

I know you hate it, because it's not explicitly stated in ACPI spec, works around it a bit and so on.
But this one is:
1) safe (in respect to hardware and code)
2) a very mighty feature

Please let us implement the spec a little loose at this point, M$ is also doing it at other parts. Let's get some fruits not always the stones...

Thanks,

Thomas

Thanks for the feedback, Thomas.

My guess is that those who have active+passive cooling and want a system that stays silent more will choose to use thermal.act= override to raise their low temp fan trip point
to stay silent up to a higher temperature.

I think it will be less popular for those w/o active cooling to force their passive trip-point lower to maintain a silent system at the cost of performance -- but I'm sure there are some people who are interested in doing so, and thermal.psv will indeed let them do that if a passive trip point already exists (and it usually does).

Don't get me wrong -- I make no assumption that "ACPI spec compliance" is the end-goal here -- making users's systems useful & supportable is the end goal. However, the reality is that the vast majority of systems are validated for Windows, and so to make Linux most supportable on those systems, it is usually in our best interest to behave largely like (we imagine) Windows does on those systems. Otherwise we exercise the BIOS where it is poorly validated and run into snags.

Note that the thermal.psv in this series is writable by root at run-time. But as it requires a trip-point-changed event to get noticed after module load time, that will get you almost the feature you are looking for, but only on systems with active cooling -- the more common ones with just critical and passive will not be implementing hysteresis and thus would not
be changing trip-points at run-time. For those, you'd have to rmmod thermal and modprobe thermal to force the new passive trip point to get noticed.

I agree, if a system doesn't have a passive trip point, it would probably not be dangerous (from a HW standpoint) to invent one and layer it over this mechanism. However, I stopped short of doing that. There have been various discussions of doing something along those lines by integrating throttling with cpufreq p-states, and I wonder if instead,
a more generic mechanism in that space isn't the way to go.

Note also that thermal.act behaves like thermal.psv above. Here, however, the system, by definition, implements active trip points -- and all the functional ones I've seen implement hysteresis and thus implement trip point change events -- so you could actually scribble on this thermal.act at run-time and it would become effective upon the next trip event. Yes, providing this override was a compromise. I stopped short of overrides for all possible active trips b/c I didn't want to get tangled in the hysteresis mess, and I figured the lowest trip point is the one of of most interest to those trying to run completely silent. Even this single trip-point override is not fool-proof, as there is no guarantee that the BIOS will actually send an event at the temperature that this gets set to. However, it does handle the most interesting trivial case of allowing us to ignore such an event when we don't want to turn the fan on as soon as the BIOS default setting.

thanks,
-Len