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Diffstat (limited to 'Documentation/hwmon/dell-smm-hwmon.rst')
| -rw-r--r-- | Documentation/hwmon/dell-smm-hwmon.rst | 66 |
1 files changed, 41 insertions, 25 deletions
diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst index 977263cb57a8..3e4e2d916ac5 100644 --- a/Documentation/hwmon/dell-smm-hwmon.rst +++ b/Documentation/hwmon/dell-smm-hwmon.rst @@ -32,13 +32,13 @@ Temperature sensors and fans can be queried and set via the standard =============================== ======= ======================================= Name Perm Description =============================== ======= ======================================= -fan[1-3]_input RO Fan speed in RPM. -fan[1-3]_label RO Fan label. -fan[1-3]_min RO Minimal Fan speed in RPM -fan[1-3]_max RO Maximal Fan speed in RPM -fan[1-3]_target RO Expected Fan speed in RPM -pwm[1-3] RW Control the fan PWM duty-cycle. -pwm1_enable WO Enable or disable automatic BIOS fan +fan[1-4]_input RO Fan speed in RPM. +fan[1-4]_label RO Fan label. +fan[1-4]_min RO Minimal Fan speed in RPM +fan[1-4]_max RO Maximal Fan speed in RPM +fan[1-4]_target RO Expected Fan speed in RPM +pwm[1-4] RW Control the fan PWM duty-cycle. +pwm[1-4]_enable RW/WO Enable or disable automatic BIOS fan control (not supported on all laptops, see below for details). temp[1-10]_input RO Temperature reading in milli-degrees @@ -49,26 +49,40 @@ temp[1-10]_label RO Temperature sensor label. Due to the nature of the SMM interface, each pwmX attribute controls fan number X. -Disabling automatic BIOS fan control ------------------------------------- +Enabling/Disabling automatic BIOS fan control +--------------------------------------------- -On some laptops the BIOS automatically sets fan speed every few -seconds. Therefore the fan speed set by mean of this driver is quickly -overwritten. +There exist two methods for enabling/disabling automatic BIOS fan control: -There is experimental support for disabling automatic BIOS fan -control, at least on laptops where the corresponding SMM command is -known, by writing the value ``1`` in the attribute ``pwm1_enable`` -(writing ``2`` enables automatic BIOS control again). Even if you have -more than one fan, all of them are set to either enabled or disabled -automatic fan control at the same time and, notwithstanding the name, -``pwm1_enable`` sets automatic control for all fans. +1. Separate SMM commands to enable/disable automatic BIOS fan control for all fans. -If ``pwm1_enable`` is not available, then it means that SMM codes for -enabling and disabling automatic BIOS fan control are not whitelisted -for your hardware. It is possible that codes that work for other -laptops actually work for yours as well, or that you have to discover -new codes. +2. A special fan state that enables automatic BIOS fan control for a individual fan. + +The driver cannot reliably detect what method should be used on a given +device, so instead the following heuristic is used: + +- use fan state 3 for enabling BIOS fan control if the maximum fan state + setable by the user is smaller than 3 (default setting). + +- use separate SMM commands if device is whitelisted to support them. + +When using the first method, each fan will have a standard ``pwmX_enable`` +sysfs attribute. Writing ``1`` into this attribute will disable automatic +BIOS fan control for the associated fan and set it to maximum speed. Enabling +BIOS fan control again can be achieved by writing ``2`` into this attribute. +Reading this sysfs attributes returns the current setting as reported by +the underlying hardware. + +When using the second method however, only the ``pwm1_enable`` sysfs attribute +will be available to enable/disable automatic BIOS fan control globaly for all +fans available on a given device. Additionally, this sysfs attribute is write-only +as there exists no SMM command for reading the current fan control setting. + +If no ``pwmX_enable`` attributes are available, then it means that the driver +cannot use the first method and the SMM codes for enabling and disabling automatic +BIOS fan control are not whitelisted for your device. It is possible that codes +that work for other laptops actually work for yours as well, or that you have to +discover new codes. Check the list ``i8k_whitelist_fan_control`` in file ``drivers/hwmon/dell-smm-hwmon.c`` in the kernel tree: as a first @@ -93,7 +107,7 @@ Again, when you find new codes, we'd be happy to have your patches! --------------------------- The driver also exports the fans as thermal cooling devices with -``type`` set to ``dell-smm-fan[1-3]``. This allows for easy fan control +``type`` set to ``dell-smm-fan[1-4]``. This allows for easy fan control using one of the thermal governors. Module parameters @@ -360,6 +374,8 @@ Firmware Bug Affected Machines ======================================================= ================= Reading of fan states return spurious errors. Precision 490 + OptiPlex 7060 + Reading of fan types causes erratic fan behaviour. Studio XPS 8000 Studio XPS 8100 |