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Date:   Tue, 15 Feb 2022 20:19:41 +0100
From:   Pali =?utf-8?B?Um9ow6Fy?= <pali@kernel.org>
To:     Armin Wolf <W_Armin@gmx.de>
Cc:     jdelvare@suse.com, linux@roeck-us.net, linux-hwmon@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/7] hwmon: (dell-smm) Allow for specifying fan control
 method as module parameter
Message-ID: <20220215191941.azk5gpcn42ahcnna@pali>
References: <20220215191113.16640-1-W_Armin@gmx.de>
 <20220215191113.16640-2-W_Armin@gmx.de>
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On Tuesday 15 February 2022 20:11:07 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 may be too cumbersome for
> the average user.

There is also another way suitable for testing purposes which do not
requires any kernel patch. Call iopl(3) syscall which changes I/O
privilege level to 3 and which allows to poke I/O registers.

> Allow for specifying the desired fan mode control method when loading
> the module, but taint the kernel if so since there is the possibility
> for strange side effects on non-whitelisted models.
> Also update docs and kernel-parameters.txt accordingly.
> 
> Tested on a Dell Inspiron 3505.
> 
> Signed-off-by: Armin Wolf <W_Armin@gmx.de>
> ---
>  .../admin-guide/kernel-parameters.txt         |  3 +++
>  Documentation/hwmon/dell-smm-hwmon.rst        | 21 ++++++++++------
>  drivers/hwmon/dell-smm-hwmon.c                | 25 +++++++++++++------
>  3 files changed, 35 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index d68053db21cc..4f1b6c2b7ed1 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -968,6 +968,9 @@
>  	dell_smm_hwmon.fan_max=
>  			[HW] Maximum configurable fan speed.
> 
> +	dell_smm_hwmon.fan_mode_method=
> +			[HW] Method to use for changing fan mode.
> +
>  	dfltcc=		[HW,S390]
>  			Format: { on | off | def_only | inf_only | always }
>  			on:       s390 zlib hardware support for compression on
> diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst
> index beec88491171..564d99cda869 100644
> --- a/Documentation/hwmon/dell-smm-hwmon.rst
> +++ b/Documentation/hwmon/dell-smm-hwmon.rst
> @@ -67,13 +67,16 @@ 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
> +As a first step, you can load the module with the module parameter
> +``fan_mode_method`` set to 1 to test if your hardware works with
> +an already know method for disabling automatic BIOS fan control.
> +If ``pwm1_enable`` is now 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.
> +Just add your model to the list ``i8k_whitelist_fan_control`` in
> +file ``drivers/hwmon/dell-smm-hwmon.c`` in the kernel tree and use
> +the already known code pair.
> +Please read
>  :ref:`Documentation/process/submitting-patches.rst <submittingpatches>`
>  for information on submitting patches.
> 
> @@ -120,6 +123,10 @@ Module parameters
>                     Maximum configurable fan speed. (default:
>                     autodetect)
> 
> +* fan_mode_method:uint
> +                   Method to use for changing fan mode (default:
> +                   from whitelist)
> +
>  Legacy ``/proc`` interface
>  --------------------------
> 
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index 9949eeb79378..1c4cc516c8b2 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -111,6 +111,10 @@ static uint fan_max;
>  module_param(fan_max, uint, 0);
>  MODULE_PARM_DESC(fan_max, "Maximum configurable fan speed (default: autodetect)");
> 
> +static uint fan_mode_method;
> +module_param_unsafe(fan_mode_method, uint, 0);
> +MODULE_PARM_DESC(fan_mode_method, "Method to use for changing fan mode (default: from whitelist)");

No, please really do not introduce another kernel parameter for this
driver. There are already many and we do not need to extend this list.

> +
>  struct smm_regs {
>  	unsigned int eax;
>  	unsigned int ebx;
> @@ -677,7 +681,7 @@ 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
> @@ -1282,14 +1286,21 @@ 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);
> 
> -	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;
> +	/* value specified via module param overrides whitelist */
> +	if (fan_mode_method > 0 && fan_mode_method <= ARRAY_SIZE(i8k_fan_control_data)) {
> +		data->manual_fan = i8k_fan_control_data[fan_mode_method - 1].manual_fan;
> +		data->auto_fan = i8k_fan_control_data[fan_mode_method - 1].auto_fan;
> +	} else {
> +		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;
> -		dev_info(&pdev->dev, "enabling support for setting automatic/manual fan control\n");
> +			data->manual_fan = control->manual_fan;
> +			data->auto_fan = control->auto_fan;
> +		}
>  	}
> +	if (data->manual_fan && data->auto_fan)
> +		dev_info(&pdev->dev, "enabling support for setting automatic/manual fan control\n");
> 
>  	if (!fan_mult) {
>  		/*
> --
> 2.30.2
>