.. SPDX-License-Identifier: GPL-2.0-or-later .. include:: Kernel driver dell-smm-hwmon ============================ :Copyright: |copy| 2002-2005 Massimo Dal Zotto :Copyright: |copy| 2019 Giovanni Mascellani 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 ` 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.