[PATCH 1/7] hwmon: (dell-smm) Allow for specifying fan control method as module parameter

[Armin Wolf <W_Armin@gmx.de>]

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.
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)");
+
 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