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