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git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
hwmon: (dell-smm) Add support for automatic fan mode
Many machines treat fan state 3 as some sort of automatic mode,
which is superior to the separate SMM calls for switching to
automatic fan mode for two reasons:
- the fan control mode can be controlled for each fan separately
- the current fan control mode can be retrieved from the BIOS
On some machines however, this special fan state does not exist.
Fan state 3 acts like a regular fan state on such machines or
does not exist at all. Such machines usually use separate SMM calls
for enabling/disabling automatic fan control.
Add support for it. If the machine supports separate SMM calls
for changing the fan control mode, then the other interface is
ignored.
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20250917181036.10972-4-W_Armin@gmx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
authored by
Armin Wolf
and committed by
Guenter Roeck
1c165805
205c7302
+95
-31
+32
-18
Documentation/hwmon/dell-smm-hwmon.rst
+32
-18
Documentation/hwmon/dell-smm-hwmon.rst
···
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fan[1-4]_max RO Maximal Fan speed in RPM
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fan[1-4]_target RO Expected Fan speed in RPM
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pwm[1-4] RW Control the fan PWM duty-cycle.
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-
pwm1_enable WO Enable or disable automatic BIOS fan
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+
pwm[1-4]_enable RW/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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Due to the nature of the SMM interface, each pwmX attribute controls
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fan number X.
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-
Disabling automatic BIOS fan control
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-
------------------------------------
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+
Enabling/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 exist two methods for enabling/disabling automatic BIOS fan control:
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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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1. Separate SMM commands to enable/disable automatic BIOS fan 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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2. A special fan state that enables automatic BIOS fan control for a individual fan.
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+
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The driver cannot reliably detect what method should be used on a given
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device, so instead the following heuristic is used:
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- use fan state 3 for enabling BIOS fan control if the maximum fan state
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setable by the user is smaller than 3 (default setting).
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+
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- use separate SMM commands if device is whitelisted to support them.
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+
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+
When using the first method, each fan will have a standard ``pwmX_enable``
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sysfs attribute. Writing ``1`` into this attribute will disable automatic
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BIOS fan control for the associated fan and set it to maximum speed. Enabling
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BIOS fan control again can be achieved by writing ``2`` into this attribute.
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Reading this sysfs attributes returns the current setting as reported by
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the underlying hardware.
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+
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When using the second method however, only the ``pwm1_enable`` sysfs attribute
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will be available to enable/disable automatic BIOS fan control globaly for all
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fans available on a given device. Additionally, this sysfs attribute is write-only
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+
as there exists no SMM command for reading the current fan control setting.
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+
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If no ``pwmX_enable`` attributes are available, then it means that the driver
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cannot use the first method and the SMM codes for enabling and disabling automatic
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BIOS fan control are not whitelisted for your device. It is possible that codes
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that work for other laptops actually work for yours as well, or that you have to
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discover 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
+61
-13
drivers/hwmon/dell-smm-hwmon.c
+61
-13
drivers/hwmon/dell-smm-hwmon.c
···
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if (ret < 0)
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return ret;
766
766
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+
/*
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+
* A fan state bigger than i8k_fan_max might indicate that
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+
* the fan is currently in automatic mode.
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*/
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+
if (ret > cdata->data->i8k_fan_max)
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return -ENODATA;
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+
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*state = ret;
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return 0;
···
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break;
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case hwmon_pwm_enable:
861
-
if (auto_fan)
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+
if (auto_fan) {
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+
/*
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+
* The setting affects all fans, so only create a
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+
* single attribute.
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+
*/
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+
if (channel != 1)
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return 0;
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+
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/*
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* There is no command for retrieve the current status
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* from BIOS, and userspace/firmware itself can change
···
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* Thus we can only provide write-only access for now.
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*/
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return 0200;
862
+
}
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+
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+
if (data->fan[channel] && data->i8k_fan_max < I8K_FAN_AUTO)
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return 0644;
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break;
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default:
···
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}
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break;
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case hwmon_pwm:
931
+
ret = i8k_get_fan_status(data, channel);
932
+
if (ret < 0)
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+
return ret;
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+
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switch (attr) {
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case hwmon_pwm_input:
951
-
ret = i8k_get_fan_status(data, channel);
952
-
if (ret < 0)
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-
return ret;
937
+
/*
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* A fan state bigger than i8k_fan_max might indicate that
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* the fan is currently in automatic mode.
940
+
*/
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+
if (ret > data->i8k_fan_max)
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+
return -ENODATA;
954
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*val = clamp_val(ret * data->i8k_pwm_mult, 0, 255);
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+
946
+
return 0;
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+
case hwmon_pwm_enable:
948
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if (ret == I8K_FAN_AUTO)
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+
*val = 2;
950
+
else
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+
*val = 1;
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return 0;
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default:
···
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return 0;
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case hwmon_pwm_enable:
1057
-
if (!val)
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-
return -EINVAL;
1059
-
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-
if (val == 1)
1025
+
switch (val) {
1026
+
case 1:
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1027
enable = false;
1062
-
else
1028
+
break;
1029
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case 2:
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enable = true;
1031
+
break;
1032
+
default:
1033
+
return -EINVAL;
1034
+
}
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mutex_lock(&data->i8k_mutex);
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-
err = i8k_enable_fan_auto_mode(data, enable);
1037
+
if (auto_fan) {
1038
+
err = i8k_enable_fan_auto_mode(data, enable);
1039
+
} else {
1040
+
/*
1041
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* When putting the fan into manual control mode we have to ensure
1042
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* that the device does not overheat until the userspace fan control
1043
+
* software takes over. Because of this we set the fan speed to
1044
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* i8k_fan_max when disabling automatic fan control.
1045
+
*/
1046
+
if (enable)
1047
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err = i8k_set_fan(data, channel, I8K_FAN_AUTO);
1048
+
else
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err = i8k_set_fan(data, channel, data->i8k_fan_max);
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+
}
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mutex_unlock(&data->i8k_mutex);
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1069
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if (err < 0)
···
1130
1082
),
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HWMON_CHANNEL_INFO(pwm,
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HWMON_PWM_INPUT | HWMON_PWM_ENABLE,
1133
-
HWMON_PWM_INPUT,
1134
-
HWMON_PWM_INPUT,
1135
-
HWMON_PWM_INPUT
1085
+
HWMON_PWM_INPUT | HWMON_PWM_ENABLE,
1086
+
HWMON_PWM_INPUT | HWMON_PWM_ENABLE,
1087
+
HWMON_PWM_INPUT | HWMON_PWM_ENABLE
1136
1088
),
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NULL
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1090
};