1.. SPDX-License-Identifier: GPL-2.0-or-later
2
3.. include:: <isonum.txt>
4
5Kernel driver dell-smm-hwmon
6============================
7
8:Copyright: |copy| 2002-2005 Massimo Dal Zotto <dz@debian.org>
9:Copyright: |copy| 2019 Giovanni Mascellani <gio@debian.org>
10
11Description
12-----------
13
14On many Dell laptops the System Management Mode (SMM) BIOS can be
15queried for the status of fans and temperature sensors.  Userspace
16utilities like ``sensors`` can be used to return the readings. The
17userspace suite `i8kutils`__ can also be used to read the sensors and
18automatically adjust fan speed (please notice that it currently uses
19the deprecated ``/proc/i8k`` interface).
20
21 __ https://github.com/vitorafsr/i8kutils
22
23``sysfs`` interface
24-------------------
25
26Temperature sensors and fans can be queried and set via the standard
27``hwmon`` interface on ``sysfs``, under the directory
28``/sys/class/hwmon/hwmonX`` for some value of ``X`` (search for the
29``X`` such that ``/sys/class/hwmon/hwmonX/name`` has content
30``dell_smm``). A number of other attributes can be read or written:
31
32=============================== ======= =======================================
33Name				Perm	Description
34=============================== ======= =======================================
35fan[1-3]_input                  RO      Fan speed in RPM.
36fan[1-3]_label                  RO      Fan label.
37pwm[1-3]                        RW      Control the fan PWM duty-cycle.
38pwm1_enable                     WO      Enable or disable automatic BIOS fan
39                                        control (not supported on all laptops,
40                                        see below for details).
41temp[1-10]_input                RO      Temperature reading in milli-degrees
42                                        Celsius.
43temp[1-10]_label                RO      Temperature sensor label.
44=============================== ======= =======================================
45
46Disabling automatic BIOS fan control
47------------------------------------
48
49On some laptops the BIOS automatically sets fan speed every few
50seconds. Therefore the fan speed set by mean of this driver is quickly
51overwritten.
52
53There is experimental support for disabling automatic BIOS fan
54control, at least on laptops where the corresponding SMM command is
55known, by writing the value ``1`` in the attribute ``pwm1_enable``
56(writing ``2`` enables automatic BIOS control again). Even if you have
57more than one fan, all of them are set to either enabled or disabled
58automatic fan control at the same time and, notwithstanding the name,
59``pwm1_enable`` sets automatic control for all fans.
60
61If ``pwm1_enable`` is not available, then it means that SMM codes for
62enabling and disabling automatic BIOS fan control are not whitelisted
63for your hardware. It is possible that codes that work for other
64laptops actually work for yours as well, or that you have to discover
65new codes.
66
67Check the list ``i8k_whitelist_fan_control`` in file
68``drivers/hwmon/dell-smm-hwmon.c`` in the kernel tree: as a first
69attempt you can try to add your machine and use an already-known code
70pair. If, after recompiling the kernel, you see that ``pwm1_enable``
71is present and works (i.e., you can manually control the fan speed),
72then please submit your finding as a kernel patch, so that other users
73can benefit from it. Please see
74:ref:`Documentation/process/submitting-patches.rst <submittingpatches>`
75for information on submitting patches.
76
77If no known code works on your machine, you need to resort to do some
78probing, because unfortunately Dell does not publish datasheets for
79its SMM. You can experiment with the code in `this repository`__ to
80probe the BIOS on your machine and discover the appropriate codes.
81
82 __ https://github.com/clopez/dellfan/
83
84Again, when you find new codes, we'd be happy to have your patches!
85
86Module parameters
87-----------------
88
89* force:bool
90                   Force loading without checking for supported
91                   models. (default: 0)
92
93* ignore_dmi:bool
94                   Continue probing hardware even if DMI data does not
95                   match. (default: 0)
96
97* restricted:bool
98                   Allow fan control only to processes with the
99                   ``CAP_SYS_ADMIN`` capability set or processes run
100                   as root when using the legacy ``/proc/i8k``
101                   interface. In this case normal users will be able
102                   to read temperature and fan status but not to
103                   control the fan.  If your notebook is shared with
104                   other users and you don't trust them you may want
105                   to use this option. (default: 1, only available
106                   with ``CONFIG_I8K``)
107
108* power_status:bool
109                   Report AC status in ``/proc/i8k``. (default: 0,
110                   only available with ``CONFIG_I8K``)
111
112* fan_mult:uint
113                   Factor to multiply fan speed with. (default:
114                   autodetect)
115
116* fan_max:uint
117                   Maximum configurable fan speed. (default:
118                   autodetect)
119
120Legacy ``/proc`` interface
121--------------------------
122
123.. warning:: This interface is obsolete and deprecated and should not
124             used in new applications. This interface is only
125             available when kernel is compiled with option
126             ``CONFIG_I8K``.
127
128The information provided by the kernel driver can be accessed by
129simply reading the ``/proc/i8k`` file. For example::
130
131    $ cat /proc/i8k
132    1.0 A17 2J59L02 52 2 1 8040 6420 1 2
133
134The fields read from ``/proc/i8k`` are::
135
136    1.0 A17 2J59L02 52 2 1 8040 6420 1 2
137    |   |   |       |  | | |    |    | |
138    |   |   |       |  | | |    |    | +------- 10. buttons status
139    |   |   |       |  | | |    |    +--------- 9.  AC status
140    |   |   |       |  | | |    +-------------- 8.  fan0 RPM
141    |   |   |       |  | | +------------------- 7.  fan1 RPM
142    |   |   |       |  | +--------------------- 6.  fan0 status
143    |   |   |       |  +----------------------- 5.  fan1 status
144    |   |   |       +-------------------------- 4.  temp0 reading (Celsius)
145    |   |   +---------------------------------- 3.  Dell service tag (later known as 'serial number')
146    |   +-------------------------------------- 2.  BIOS version
147    +------------------------------------------ 1.  /proc/i8k format version
148
149A negative value, for example -22, indicates that the BIOS doesn't
150return the corresponding information. This is normal on some
151models/BIOSes.
152
153For performance reasons the ``/proc/i8k`` doesn't report by default
154the AC status since this SMM call takes a long time to execute and is
155not really needed.  If you want to see the ac status in ``/proc/i8k``
156you must explictitly enable this option by passing the
157``power_status=1`` parameter to insmod. If AC status is not
158available -1 is printed instead.
159
160The driver provides also an ioctl interface which can be used to
161obtain the same information and to control the fan status. The ioctl
162interface can be accessed from C programs or from shell using the
163i8kctl utility. See the source file of ``i8kutils`` for more
164information on how to use the ioctl interface.
165