diff options
authorLen Brown <>2007-08-12 00:12:26 -0400
committerLen Brown <>2007-08-12 00:12:26 -0400
commit730ff34de766a6fddee25ac1c32bc49c1a2fd758 (patch)
parent72b33ef8bb1ac7f6c5a16d23304ab25ddc73d93d (diff)
ACPI: thermal: expose "thermal.tzp=" to set global polling frequency
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 OS poll the thermal zone 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. High volume OS's from this century never poll any thermal zones Ie. The OS depends on the platform's ability to provoke thermal events when necessary, and the "OS provided default frequency" is "never":-) There is a proposal that ACPI 4.0 be updated to reflect common industry practice -- ie. no _TZP, no polling. The Linux kernel already follows this 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 preventing 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, to simplify debugging those broken platforms. Note that thermal.tzp is a module-load time parameter only. Signed-off-by: Len Brown <>
2 files changed, 6 insertions, 1 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index de3300c9056..ed7d7913af8 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1823,6 +1823,11 @@ and is between 256 and 4096 characters. It is defined in the file [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']
diff --git a/drivers/acpi/thermal.c b/drivers/acpi/thermal.c
index 61337d969d7..b6b3bec8454 100644
--- a/drivers/acpi/thermal.c
+++ b/drivers/acpi/thermal.c
@@ -75,7 +75,7 @@ MODULE_DESCRIPTION("ACPI Thermal Zone Driver");
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;