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diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst new file mode 100644 index 000000000..d8f1d6859 --- /dev/null +++ b/Documentation/hwmon/dell-smm-hwmon.rst @@ -0,0 +1,359 @@ +.. 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. +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 + 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. +=============================== ======= ======================================= + +Due to the nature of the SMM interface, each pwmX attribute controls +fan number X. + +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! + +``thermal`` interface +--------------------------- + +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 +using one of the thermal governors. + +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. + +SMM Interface +------------- + +.. warning:: The SMM interface was reverse-engineered by trial-and-error + since Dell did not provide any Documentation, + please keep that in mind. + +The driver uses the SMM interface to send commands to the system BIOS. +This interface is normally used by Dell's 32-bit diagnostic program or +on newer notebook models by the buildin BIOS diagnostics. +The SMM is triggered by writing to the special ioports ``0xb2`` and ``0x84``, +and may cause short hangs when the BIOS code is taking too long to +execute. + +The SMM handler inside the system BIOS looks at the contents of the +``eax``, ``ebx``, ``ecx``, ``edx``, ``esi`` and ``edi`` registers. +Each register has a special purpose: + +=============== ================================== +Register Purpose +=============== ================================== +eax Holds the command code before SMM, + holds the first result after SMM. +ebx Holds the arguments. +ecx Unknown, set to 0. +edx Holds the second result after SMM. +esi Unknown, set to 0. +edi Unknown, set to 0. +=============== ================================== + +The SMM handler can signal a failure by either: + +- setting the lower sixteen bits of ``eax`` to ``0xffff`` +- not modifying ``eax`` at all +- setting the carry flag + +SMM command codes +----------------- + +=============== ======================= ================================================ +Command Code Command Name Description +=============== ======================= ================================================ +``0x0025`` Get Fn key status Returns the Fn key pressed after SMM: + + - 9th bit in ``eax`` indicates Volume up + - 10th bit in ``eax`` indicates Volume down + - both bits indicate Volume mute + +``0xa069`` Get power status Returns current power status after SMM: + + - 1st bit in ``eax`` indicates Battery connected + - 3th bit in ``eax`` indicates AC connected + +``0x00a3`` Get fan state Returns current fan state after SMM: + + - 1st byte in ``eax`` holds the current + fan state (0 - 2 or 3) + +``0x01a3`` Set fan state Sets the fan speed: + + - 1st byte in ``ebx`` holds the fan number + - 2nd byte in ``ebx`` holds the desired + fan state (0 - 2 or 3) + +``0x02a3`` Get fan speed Returns the current fan speed in RPM: + + - 1st byte in ``ebx`` holds the fan number + - 1st word in ``eax`` holds the current + fan speed in RPM (after SMM) + +``0x03a3`` Get fan type Returns the fan type: + + - 1st byte in ``ebx`` holds the fan number + - 1st byte in ``eax`` holds the + fan type (after SMM): + + - 5th bit indicates docking fan + - 1 indicates Processor fan + - 2 indicates Motherboard fan + - 3 indicates Video fan + - 4 indicates Power supply fan + - 5 indicates Chipset fan + - 6 indicates other fan type + +``0x04a3`` Get nominal fan speed Returns the nominal RPM in each fan state: + + - 1st byte in ``ebx`` holds the fan number + - 2nd byte in ``ebx`` holds the fan state + in question (0 - 2 or 3) + - 1st word in ``eax`` holds the nominal + fan speed in RPM (after SMM) + +``0x05a3`` Get fan speed tolerance Returns the speed tolerance for each fan state: + + - 1st byte in ``ebx`` holds the fan number + - 2nd byte in ``ebx`` holds the fan state + in question (0 - 2 or 3) + - 1st byte in ``eax`` returns the speed + tolerance + +``0x10a3`` Get sensor temperature Returns the measured temperature: + + - 1st byte in ``ebx`` holds the sensor number + - 1st byte in ``eax`` holds the measured + temperature (after SMM) + +``0x11a3`` Get sensor type Returns the sensor type: + + - 1st byte in ``ebx`` holds the sensor number + - 1st byte in ``eax`` holds the + temperature type (after SMM): + + - 1 indicates CPU sensor + - 2 indicates GPU sensor + - 3 indicates SODIMM sensor + - 4 indicates other sensor type + - 5 indicates Ambient sensor + - 6 indicates other sensor type + +``0xfea3`` Get SMM signature Returns Dell signature if interface + is supported (after SMM): + + - ``eax`` holds 1145651527 + (0x44494147 or "DIAG") + - ``edx`` holds 1145392204 + (0x44454c4c or "DELL") + +``0xffa3`` Get SMM signature Same as ``0xfea3``, check both. +=============== ======================= ================================================ + +There are additional commands for enabling (``0x31a3`` or ``0x35a3``) and +disabling (``0x30a3`` or ``0x34a3``) automatic fan speed control. +The commands are however causing severe sideeffects on many machines, so +they are not used by default. + +On several machines (Inspiron 3505, Precision 490, Vostro 1720, ...), the +fans supports a 4th "magic" state, which signals the BIOS that automatic +fan control should be enabled for a specific fan. +However there are also some machines who do support a 4th regular fan state too, +but in case of the "magic" state, the nominal RPM reported for this state is a +placeholder value, which however is not always detectable. + +Firmware Bugs +------------- + +The SMM calls can behave erratic on some machines: + +======================================================= ================= +Firmware Bug Affected Machines +======================================================= ================= +Reading of fan states return spurious errors. Precision 490 + +Reading of fan types causes erratic fan behaviour. Studio XPS 8000 + + Studio XPS 8100 + + Inspiron 580 + + Inspiron 3505 + +Fan-related SMM calls take too long (about 500ms). Inspiron 7720 + + Vostro 3360 + + XPS 13 9333 + + XPS 15 L502X +======================================================= ================= + +In case you experience similar issues on your Dell machine, please +submit a bugreport on bugzilla to we can apply workarounds. + +Limitations +----------- + +The SMM calls can take too long to execute on some machines, causing +short hangs and/or audio glitches. +Also the fan state needs to be restored after suspend, as well as +the automatic mode settings. +When reading a temperature sensor, values above 127 degrees indicate +a BIOS read error or a deactivated sensor. |