i8k: Autodetect fan RPM multiplier

This patch adds new function i8k_get_fan_nominal_speed() for doing SMM call
which will return nominal fan RPM for specified fan speed. It returns nominal
RPM value at which fan operate when speed (0, 1, 2, 3) is set. It looks like
RPM value is not accurate, but still provides very useful information.

New function i8k_get_fan_nominal_speed() is used for determinate if fan
multiplier is 1 or 30. If function for maximal fan value success and returned
RPM value too high (above 30000) then fan multiplier is set to 1. Otherwise
multiplier is not changed and default value 30 is used.
Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Gabriele Mazzotta <gabriele.mzt@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/i8k.c

@@ -6,6 +6,7 @@
  * Hwmon integration:
  * Copyright (C) 2011  Jean Delvare <jdelvare@suse.de>
  * Copyright (C) 2013, 2014  Guenter Roeck <linux@roeck-us.net>
+ * Copyright (C) 2014  Pali Rohár <pali.rohar@gmail.com>
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -42,12 +43,14 @@
 #define I8K_SMM_SET_FAN		0x01a3
 #define I8K_SMM_GET_FAN		0x00a3
 #define I8K_SMM_GET_SPEED	0x02a3
+#define I8K_SMM_GET_NOM_SPEED	0x04a3
 #define I8K_SMM_GET_TEMP	0x10a3
 #define I8K_SMM_GET_TEMP_TYPE	0x11a3
 #define I8K_SMM_GET_DELL_SIG1	0xfea3
 #define I8K_SMM_GET_DELL_SIG2	0xffa3
 
 #define I8K_FAN_MULT		30
+#define I8K_FAN_MAX_RPM		30000
 #define I8K_MAX_TEMP		127
 
 #define I8K_FN_NONE		0x00
@@ -64,7 +67,7 @@ static DEFINE_MUTEX(i8k_mutex);
 static char bios_version[4];
 static struct device *i8k_hwmon_dev;
 static u32 i8k_hwmon_flags;
-static uint i8k_fan_mult;
+static uint i8k_fan_mult = I8K_FAN_MULT;
 static uint i8k_pwm_mult;
 static uint i8k_fan_max = I8K_FAN_HIGH;
 
@@ -95,13 +98,13 @@ static bool power_status;
 module_param(power_status, bool, 0600);
 MODULE_PARM_DESC(power_status, "Report power status in /proc/i8k");
 
-static uint fan_mult = I8K_FAN_MULT;
+static uint fan_mult;
 module_param(fan_mult, uint, 0);
-MODULE_PARM_DESC(fan_mult, "Factor to multiply fan speed with");
+MODULE_PARM_DESC(fan_mult, "Factor to multiply fan speed with (default: autodetect)");
 
-static uint fan_max = I8K_FAN_HIGH;
+static uint fan_max;
 module_param(fan_max, uint, 0);
-MODULE_PARM_DESC(fan_max, "Maximum configurable fan speed");
+MODULE_PARM_DESC(fan_max, "Maximum configurable fan speed (default: autodetect)");
 
 static int i8k_open_fs(struct inode *inode, struct file *file);
 static long i8k_ioctl(struct file *, unsigned int, unsigned long);
@@ -275,6 +278,17 @@ static int i8k_get_fan_speed(int fan)
 	return i8k_smm(&regs) ? : (regs.eax & 0xffff) * i8k_fan_mult;
 }
 
+/*
+ * Read the fan nominal rpm for specific fan speed.
+ */
+static int i8k_get_fan_nominal_speed(int fan, int speed)
+{
+	struct smm_regs regs = { .eax = I8K_SMM_GET_NOM_SPEED, };
+
+	regs.ebx = (fan & 0xff) | (speed << 8);
+	return i8k_smm(&regs) ? : (regs.eax & 0xffff) * i8k_fan_mult;
+}
+
 /*
  * Set the fan speed (off, low, high). Returns the new fan status.
  */
@@ -863,6 +877,7 @@ MODULE_DEVICE_TABLE(dmi, i8k_dmi_table);
 static int __init i8k_probe(void)
 {
 	const struct dmi_system_id *id;
+	int fan, ret;
 
 	/*
 	 * Get DMI information
@@ -891,19 +906,40 @@ static int __init i8k_probe(void)
 			return -ENODEV;
 	}
 
-	i8k_fan_mult = fan_mult;
-	i8k_fan_max = fan_max ? : I8K_FAN_HIGH;	/* Must not be 0 */
+	/*
+	 * Set fan multiplier and maximal fan speed from dmi config
+	 * Values specified in module parameters override values from dmi
+	 */
 	id = dmi_first_match(i8k_dmi_table);
 	if (id && id->driver_data) {
 		const struct i8k_config_data *conf = id->driver_data;
-
-		if (fan_mult == I8K_FAN_MULT && conf->fan_mult)
-			i8k_fan_mult = conf->fan_mult;
-		if (fan_max == I8K_FAN_HIGH && conf->fan_max)
-			i8k_fan_max = conf->fan_max;
+		if (!fan_mult && conf->fan_mult)
+			fan_mult = conf->fan_mult;
+		if (!fan_max && conf->fan_max)
+			fan_max = conf->fan_max;
 	}
+
+	i8k_fan_max = fan_max ? : I8K_FAN_HIGH;	/* Must not be 0 */
 	i8k_pwm_mult = DIV_ROUND_UP(255, i8k_fan_max);
 
+	if (!fan_mult) {
+		/*
+		 * Autodetect fan multiplier based on nominal rpm
+		 * If fan reports rpm value too high then set multiplier to 1
+		 */
+		for (fan = 0; fan < 2; ++fan) {
+			ret = i8k_get_fan_nominal_speed(fan, i8k_fan_max);
+			if (ret < 0)
+				continue;
+			if (ret > I8K_FAN_MAX_RPM)
+				i8k_fan_mult = 1;
+			break;
+		}
+	} else {
+		/* Fan multiplier was specified in module param or in dmi */
+		i8k_fan_mult = fan_mult;
+	}
+
 	return 0;
 }