From 1c1658058c99bcfd3b2347e587a556986037f80a Mon Sep 17 00:00:00 2001 From: Armin Wolf Date: Wed, 17 Sep 2025 20:10:35 +0200 Subject: [PATCH] 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 Link: https://lore.kernel.org/r/20250917181036.10972-4-W_Armin@gmx.de Signed-off-by: Guenter Roeck --- Documentation/hwmon/dell-smm-hwmon.rst | 56 +++++++++++-------- drivers/hwmon/dell-smm-hwmon.c | 74 +++++++++++++++++++++----- include/uapi/linux/i8k.h | 2 + 3 files changed, 98 insertions(+), 34 deletions(-) diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst index 5a4edb6565cf9..3e4e2d916ac52 100644 --- a/Documentation/hwmon/dell-smm-hwmon.rst +++ b/Documentation/hwmon/dell-smm-hwmon.rst @@ -38,7 +38,7 @@ fan[1-4]_min RO Minimal Fan speed in RPM fan[1-4]_max RO Maximal Fan speed in RPM fan[1-4]_target RO Expected Fan speed in RPM pwm[1-4] RW Control the fan PWM duty-cycle. -pwm1_enable WO Enable or disable automatic BIOS fan +pwm[1-4]_enable RW/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 @@ -49,26 +49,40 @@ 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. +Enabling/Disabling automatic BIOS fan control +--------------------------------------------- + +There exist two methods for enabling/disabling automatic BIOS fan control: + +1. Separate SMM commands to enable/disable automatic BIOS fan control for all fans. + +2. A special fan state that enables automatic BIOS fan control for a individual fan. + +The driver cannot reliably detect what method should be used on a given +device, so instead the following heuristic is used: + +- use fan state 3 for enabling BIOS fan control if the maximum fan state + setable by the user is smaller than 3 (default setting). + +- use separate SMM commands if device is whitelisted to support them. + +When using the first method, each fan will have a standard ``pwmX_enable`` +sysfs attribute. Writing ``1`` into this attribute will disable automatic +BIOS fan control for the associated fan and set it to maximum speed. Enabling +BIOS fan control again can be achieved by writing ``2`` into this attribute. +Reading this sysfs attributes returns the current setting as reported by +the underlying hardware. + +When using the second method however, only the ``pwm1_enable`` sysfs attribute +will be available to enable/disable automatic BIOS fan control globaly for all +fans available on a given device. Additionally, this sysfs attribute is write-only +as there exists no SMM command for reading the current fan control setting. + +If no ``pwmX_enable`` attributes are available, then it means that the driver +cannot use the first method and the SMM codes for enabling and disabling automatic +BIOS fan control are not whitelisted for your device. 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 diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c index 36576db097067..79befa13b6990 100644 --- a/drivers/hwmon/dell-smm-hwmon.c +++ b/drivers/hwmon/dell-smm-hwmon.c @@ -764,6 +764,13 @@ static int dell_smm_get_cur_state(struct thermal_cooling_device *dev, unsigned l if (ret < 0) return ret; + /* + * A fan state bigger than i8k_fan_max might indicate that + * the fan is currently in automatic mode. + */ + if (ret > cdata->data->i8k_fan_max) + return -ENODATA; + *state = ret; return 0; @@ -851,7 +858,14 @@ static umode_t dell_smm_is_visible(const void *drvdata, enum hwmon_sensor_types break; case hwmon_pwm_enable: - if (auto_fan) + if (auto_fan) { + /* + * The setting affects all fans, so only create a + * single attribute. + */ + if (channel != 1) + return 0; + /* * There is no command for retrieve the current status * from BIOS, and userspace/firmware itself can change @@ -859,6 +873,10 @@ static umode_t dell_smm_is_visible(const void *drvdata, enum hwmon_sensor_types * Thus we can only provide write-only access for now. */ return 0200; + } + + if (data->fan[channel] && data->i8k_fan_max < I8K_FAN_AUTO) + return 0644; break; default: @@ -928,14 +946,28 @@ static int dell_smm_read(struct device *dev, enum hwmon_sensor_types type, u32 a } break; case hwmon_pwm: + ret = i8k_get_fan_status(data, channel); + if (ret < 0) + return ret; + switch (attr) { case hwmon_pwm_input: - ret = i8k_get_fan_status(data, channel); - if (ret < 0) - return ret; + /* + * A fan state bigger than i8k_fan_max might indicate that + * the fan is currently in automatic mode. + */ + if (ret > data->i8k_fan_max) + return -ENODATA; *val = clamp_val(ret * data->i8k_pwm_mult, 0, 255); + return 0; + case hwmon_pwm_enable: + if (ret == I8K_FAN_AUTO) + *val = 2; + else + *val = 1; + return 0; default: break; @@ -1022,16 +1054,32 @@ static int dell_smm_write(struct device *dev, enum hwmon_sensor_types type, u32 return 0; case hwmon_pwm_enable: - if (!val) - return -EINVAL; - - if (val == 1) + switch (val) { + case 1: enable = false; - else + break; + case 2: enable = true; + break; + default: + return -EINVAL; + } mutex_lock(&data->i8k_mutex); - err = i8k_enable_fan_auto_mode(data, enable); + if (auto_fan) { + err = i8k_enable_fan_auto_mode(data, enable); + } else { + /* + * When putting the fan into manual control mode we have to ensure + * that the device does not overheat until the userspace fan control + * software takes over. Because of this we set the fan speed to + * i8k_fan_max when disabling automatic fan control. + */ + if (enable) + err = i8k_set_fan(data, channel, I8K_FAN_AUTO); + else + err = i8k_set_fan(data, channel, data->i8k_fan_max); + } mutex_unlock(&data->i8k_mutex); if (err < 0) @@ -1082,9 +1130,9 @@ static const struct hwmon_channel_info * const dell_smm_info[] = { ), HWMON_CHANNEL_INFO(pwm, HWMON_PWM_INPUT | HWMON_PWM_ENABLE, - HWMON_PWM_INPUT, - HWMON_PWM_INPUT, - HWMON_PWM_INPUT + HWMON_PWM_INPUT | HWMON_PWM_ENABLE, + HWMON_PWM_INPUT | HWMON_PWM_ENABLE, + HWMON_PWM_INPUT | HWMON_PWM_ENABLE ), NULL }; diff --git a/include/uapi/linux/i8k.h b/include/uapi/linux/i8k.h index 268e6268f6c80..a16e4049710fc 100644 --- a/include/uapi/linux/i8k.h +++ b/include/uapi/linux/i8k.h @@ -36,6 +36,8 @@ #define I8K_FAN_LOW 1 #define I8K_FAN_HIGH 2 #define I8K_FAN_TURBO 3 +/* Many machines treat this mode as some sort of automatic mode */ +#define I8K_FAN_AUTO 3 #define I8K_FAN_MAX I8K_FAN_TURBO #define I8K_VOL_UP 1 -- 2.47.3