| Copyright: | |copy| 2002-2005 Massimo Dal Zotto <[email protected]> |
|---|---|
| Copyright: | |copy| 2019 Giovanni Mascellani <[email protected]> |
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).
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.
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.
Again, when you find new codes, we'd be happy to have your patches!
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.
- 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_ADMINcapability set or processes run as root when using the legacy/proc/i8kinterface. 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 withCONFIG_I8K)
- power_status:bool
- Report AC status in
/proc/i8k. (default: 0, only available withCONFIG_I8K)
- fan_mult:uint
- Factor to multiply fan speed with. (default: autodetect)
- fan_max:uint
- Maximum configurable fan speed. (default: autodetect)
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.
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
eaxto0xffff - not modifying
eaxat all - setting the carry flag
| Command Code | Command Name | Description |
|---|---|---|
0x0025 |
Get Fn key status | Returns the Fn key pressed after SMM:
|
0xa069 |
Get power status | Returns current power status after SMM:
|
0x00a3 |
Get fan state | Returns current fan state after SMM:
|
0x01a3 |
Set fan state | Sets the fan speed:
|
0x02a3 |
Get fan speed | Returns the current fan speed in RPM:
|
0x03a3 |
Get fan type | Returns the fan type:
|
0x04a3 |
Get nominal fan speed | Returns the nominal RPM in each fan state:
|
0x05a3 |
Get fan speed tolerance | Returns the speed tolerance for each fan state:
|
0x10a3 |
Get sensor temperature | Returns the measured temperature:
|
0x11a3 |
Get sensor type | Returns the sensor type:
|
0xfea3 |
Get SMM signature | Returns Dell signature if interface is supported (after SMM):
|
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.
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.
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.