Re: [RFC] hwmon: (dell-smm) Allow for specifying fan control commands as module params

[Guenter Roeck]

On 10/26/21 10:18 AM, Armin Wolf wrote:
> Right now, the only way to test if setting manual/auto fan control works
> is to edit and recompile the module, which might not be possible for
> everyone. Allow for specifying the necessary SMM commands when loading
> the module, but taint the kernel if so since those commands might
> cause strange side effects. Also update kernel-parameters.txt
> accordingly.
>
> Tested on a Dell Inspiron 3505.
>
> Signed-off-by: Armin Wolf <W_Armin@xxxxxx>

As far as I can see there are three logical changes in this patch:
- move parameters from i8k to dell_smm_hwmon
- add documentation for undocumented parameters
- add new parameters

"One patch per logical change", please, as documented.

Thanks,
Guenter

> ---
>   .../admin-guide/kernel-parameters.txt         | 45 ++++++++++++++-----
>   Documentation/hwmon/dell-smm-hwmon.rst        | 27 ++++++++---
>   drivers/hwmon/dell-smm-hwmon.c                | 22 +++++++--
>   3 files changed, 73 insertions(+), 21 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 91ba391f9b32..7025f5bf625f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -940,6 +940,40 @@
>   			dump out devices still on the deferred probe list after
>   			retrying.
>
> +	dell_smm_hwmon.ignore_dmi=
> +			[HW] Continue probing hardware even if DMI data
> +                        indicates that the driver is running on unsupported
> +                        hardware.
> +
> +        dell_smm_hwmon.force=
> +			[HW] Activate driver even if SMM BIOS signature does
> +			not match list of supported models or certain
> +			features are disabled.
> +
> +        dell_smm_hwmon.power_status=
> +                        [HW] Report power status in /proc/i8k
> +                        (disabled by default).
> +
> +        dell_smm_hwmon.restricted=
> +			[HW] Allow controlling fans only if SYS_ADMIN
> +                        capability is set.
> +
> +	dell_smm_hwmon.fan_mult=
> +			[HW] Factor to multiply fan speed with.
> +
> +	dell_smm_hwmon.fan_max=
> +			[HW] Maximum configurable fan speed.
> +
> +	dell_smm_hwmon.manual_fan=
> +			[HW] SMM command to disable BIOS fan control, must be
> +			set together with dell_smm_hwmon.auto_fan to work.
> +			This can be dangerous, yet let us know if a certain
> +			command combination worked.
> +
> +	dell_smm_hwmon.auto_fan=
> +			[HW] SMM command to enable BIOS fan control, see
> +			dell_smm_hwmon.manual_fan for further explaination.
> +
>   	dfltcc=		[HW,S390]
>   			Format: { on | off | def_only | inf_only | always }
>   			on:       s390 zlib hardware support for compression on
> @@ -1693,17 +1727,6 @@
>
>   	i810=		[HW,DRM]
>
> -	i8k.ignore_dmi	[HW] Continue probing hardware even if DMI data
> -			indicates that the driver is running on unsupported
> -			hardware.
> -	i8k.force	[HW] Activate i8k driver even if SMM BIOS signature
> -			does not match list of supported models.
> -	i8k.power_status
> -			[HW] Report power status in /proc/i8k
> -			(disabled by default)
> -	i8k.restricted	[HW] Allow controlling fans only if SYS_ADMIN
> -			capability is set.
> -
>   	i915.invert_brightness=
>   			[DRM] Invert the sense of the variable that is used to
>   			set the brightness of the panel backlight. Normally a
> diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst
> index beec88491171..df12dce7b02e 100644
> --- a/Documentation/hwmon/dell-smm-hwmon.rst
> +++ b/Documentation/hwmon/dell-smm-hwmon.rst
> @@ -67,13 +67,13 @@ 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
> +Check the list ``i8k_fan_control_data`` in file
> +``drivers/hwmon/dell-smm-hwmon.c`` inside the kernel tree:
> +as a first attempt you can load the module with ``manual_fan`` and
> +``auto_fan`` set to an already-known code pair. If 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.
>
> @@ -120,6 +120,19 @@ Module parameters
>                      Maximum configurable fan speed. (default:
>                      autodetect)
>
> +* manual_fan:uint
> +                   SMM code to disable BIOS fan control, must
> +                   be set together with auto_fan to work.
> +                   Please note that this parameter is unsafe and
> +                   will taint your kernel when set, use only for
> +                   testing codes on your hardware!
> +                   (default: retrieved from whitelist)
> +
> +* auto_fan:uint
> +                   SMM command to enable BIOS fan control, see
> +                   manual_fan for further explaination.
> +                   (default: retrieved from whitelist)
> +
>   Legacy ``/proc`` interface
>   --------------------------
>
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index eaace478f508..4257aa297d7a 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -111,6 +111,14 @@ static uint fan_max;
>   module_param(fan_max, uint, 0);
>   MODULE_PARM_DESC(fan_max, "Maximum configurable fan speed (default: autodetect)");
>
> +static uint manual_fan;
> +module_param_unsafe(manual_fan, uint, 0);
> +MODULE_PARM_DESC(manual_fan, "SMM command to disable BIOS fan control (default: disabled)");
> +
> +static uint auto_fan;
> +module_param_unsafe(auto_fan, uint, 0);
> +MODULE_PARM_DESC(auto_fan, "SMM command to enable BIOS fan control (default: disabled)");
> +
>   struct smm_regs {
>   	unsigned int eax;
>   	unsigned int ebx __packed;
> @@ -700,7 +708,7 @@ static umode_t dell_smm_is_visible(const void *drvdata, enum hwmon_sensor_types
>
>   			break;
>   		case hwmon_pwm_enable:
> -			if (data->auto_fan)
> +			if (data->auto_fan && data->manual_fan)
>   				/*
>   				 * There is no command for retrieve the current status
>   				 * from BIOS, and userspace/firmware itself can change
> @@ -1305,12 +1313,20 @@ static int __init dell_smm_probe(struct platform_device *pdev)
>   	data->i8k_fan_max = fan_max ? : I8K_FAN_HIGH;	/* Must not be 0 */
>   	data->i8k_pwm_mult = DIV_ROUND_UP(255, data->i8k_fan_max);
>
> +	/* Values specified in module parameters override values from dmi */
>   	fan_control = dmi_first_match(i8k_whitelist_fan_control);
>   	if (fan_control && fan_control->driver_data) {
>   		const struct i8k_fan_control_data *control = fan_control->driver_data;
>
> -		data->manual_fan = control->manual_fan;
> -		data->auto_fan = control->auto_fan;
> +		if (!manual_fan)
> +			manual_fan = control->manual_fan;
> +
> +		if (!auto_fan)
> +			auto_fan = control->auto_fan;
> +	}
> +	if (manual_fan && auto_fan) {
> +		data->manual_fan = manual_fan;
> +		data->auto_fan = auto_fan;
>   		dev_info(&pdev->dev, "enabling support for setting automatic/manual fan control\n");
>   	}
>
> --
> 2.30.2