| .. SPDX-License-Identifier: GPL-2.0-or-later |
| |
| .. include:: <isonum.txt> |
| |
| Kernel driver dell-smm-hwmon |
| ============================ |
| |
| :Copyright: |copy| 2002-2005 Massimo Dal Zotto <dz@debian.org> |
| :Copyright: |copy| 2019 Giovanni Mascellani <gio@debian.org> |
| |
| Description |
| ----------- |
| |
| On many Dell laptops the System Management Mode (SMM) BIOS can be |
| queried for the status of fans and temperature sensors. Userspace |
| utilities like ``sensors`` can be used to return the readings. The |
| userspace suite `i8kutils`__ can also be used to read the sensors and |
| automatically adjust fan speed (please notice that it currently uses |
| the deprecated ``/proc/i8k`` interface). |
| |
| __ https://github.com/vitorafsr/i8kutils |
| |
| ``sysfs`` interface |
| ------------------- |
| |
| Temperature sensors and fans can be queried and set via the standard |
| ``hwmon`` interface on ``sysfs``, under the directory |
| ``/sys/class/hwmon/hwmonX`` for some value of ``X`` (search for the |
| ``X`` such that ``/sys/class/hwmon/hwmonX/name`` has content |
| ``dell_smm``). A number of other attributes can be read or written: |
| |
| =============================== ======= ======================================= |
| Name Perm Description |
| =============================== ======= ======================================= |
| fan[1-3]_input RO Fan speed in RPM. |
| fan[1-3]_label RO Fan label. |
| pwm[1-3] RW Control the fan PWM duty-cycle. |
| pwm1_enable 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 |
| Celsius. |
| temp[1-10]_label RO Temperature sensor label. |
| =============================== ======= ======================================= |
| |
| 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 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. |
| |
| 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. |
| |
| Check the list ``i8k_whitelist_fan_control`` in file |
| ``drivers/hwmon/dell-smm-hwmon.c`` in the kernel tree: as a first |
| attempt you can try to add your machine and use an already-known code |
| pair. If, after recompiling the kernel, you see that ``pwm1_enable`` |
| is present and works (i.e., you can manually control the fan speed), |
| then please submit your finding as a kernel patch, so that other users |
| can benefit from it. Please see |
| :ref:`Documentation/process/submitting-patches.rst <submittingpatches>` |
| for information on submitting patches. |
| |
| If no known code works on your machine, you need to resort to do some |
| probing, because unfortunately Dell does not publish datasheets for |
| its SMM. You can experiment with the code in `this repository`__ to |
| probe the BIOS on your machine and discover the appropriate codes. |
| |
| __ https://github.com/clopez/dellfan/ |
| |
| Again, when you find new codes, we'd be happy to have your patches! |
| |
| Module parameters |
| ----------------- |
| |
| * force:bool |
| Force loading without checking for supported |
| models. (default: 0) |
| |
| * ignore_dmi:bool |
| Continue probing hardware even if DMI data does not |
| match. (default: 0) |
| |
| * restricted:bool |
| Allow fan control only to processes with the |
| ``CAP_SYS_ADMIN`` capability set or processes run |
| as root when using the legacy ``/proc/i8k`` |
| interface. In this case normal users will be able |
| to read temperature and fan status but not to |
| control the fan. If your notebook is shared with |
| other users and you don't trust them you may want |
| to use this option. (default: 1, only available |
| with ``CONFIG_I8K``) |
| |
| * power_status:bool |
| Report AC status in ``/proc/i8k``. (default: 0, |
| only available with ``CONFIG_I8K``) |
| |
| * fan_mult:uint |
| Factor to multiply fan speed with. (default: |
| autodetect) |
| |
| * fan_max:uint |
| Maximum configurable fan speed. (default: |
| autodetect) |
| |
| Legacy ``/proc`` interface |
| -------------------------- |
| |
| .. warning:: This interface is obsolete and deprecated and should not |
| used in new applications. This interface is only |
| available when kernel is compiled with option |
| ``CONFIG_I8K``. |
| |
| The information provided by the kernel driver can be accessed by |
| simply reading the ``/proc/i8k`` file. For example:: |
| |
| $ cat /proc/i8k |
| 1.0 A17 2J59L02 52 2 1 8040 6420 1 2 |
| |
| The fields read from ``/proc/i8k`` are:: |
| |
| 1.0 A17 2J59L02 52 2 1 8040 6420 1 2 |
| | | | | | | | | | | |
| | | | | | | | | | +------- 10. buttons status |
| | | | | | | | | +--------- 9. AC status |
| | | | | | | | +-------------- 8. fan0 RPM |
| | | | | | | +------------------- 7. fan1 RPM |
| | | | | | +--------------------- 6. fan0 status |
| | | | | +----------------------- 5. fan1 status |
| | | | +-------------------------- 4. temp0 reading (Celsius) |
| | | +---------------------------------- 3. Dell service tag (later known as 'serial number') |
| | +-------------------------------------- 2. BIOS version |
| +------------------------------------------ 1. /proc/i8k format version |
| |
| A negative value, for example -22, indicates that the BIOS doesn't |
| return the corresponding information. This is normal on some |
| models/BIOSes. |
| |
| For performance reasons the ``/proc/i8k`` doesn't report by default |
| the AC status since this SMM call takes a long time to execute and is |
| not really needed. If you want to see the ac status in ``/proc/i8k`` |
| you must explictitly enable this option by passing the |
| ``power_status=1`` parameter to insmod. If AC status is not |
| available -1 is printed instead. |
| |
| The driver provides also an ioctl interface which can be used to |
| obtain the same information and to control the fan status. The ioctl |
| interface can be accessed from C programs or from shell using the |
| i8kctl utility. See the source file of ``i8kutils`` for more |
| information on how to use the ioctl interface. |
