Ok, here are new patches for testing... Those you are still reading this email 
thread and have your Dell 
machines near, can you test them (ideally with disabling dmi config data)?

diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
index 8ec4c37..d6e8a26 100644
--- a/drivers/char/i8k.c
+++ b/drivers/char/i8k.c
@@ -64,9 +64,9 @@ static DEFINE_MUTEX(i8k_mutex);
 static char bios_version[4];
 static struct device *i8k_hwmon_dev;
 static u32 i8k_hwmon_flags;
-static int i8k_fan_mult;
-static int i8k_pwm_mult;
-static int i8k_fan_max = I8K_FAN_HIGH;
+static uint i8k_fan_mult;
+static uint i8k_pwm_mult;
+static uint i8k_fan_max = I8K_FAN_HIGH;
 
 #define I8K_HWMON_HAVE_TEMP1   (1 << 0)
 #define I8K_HWMON_HAVE_TEMP2   (1 << 1)
@@ -95,12 +95,12 @@ static bool power_status;
 module_param(power_status, bool, 0600);
 MODULE_PARM_DESC(power_status, "Report power status in /proc/i8k");
 
-static int fan_mult = I8K_FAN_MULT;
-module_param(fan_mult, int, 0);
+static uint fan_mult = I8K_FAN_MULT;
+module_param(fan_mult, uint, 0);
 MODULE_PARM_DESC(fan_mult, "Factor to multiply fan speed with");
 
-static int fan_max = I8K_FAN_HIGH;
-module_param(fan_max, int, 0);
+static uint fan_max = I8K_FAN_HIGH;
+module_param(fan_max, uint, 0);
 MODULE_PARM_DESC(fan_max, "Maximum configurable fan speed");
 
 static int i8k_open_fs(struct inode *inode, struct file *file);
@@ -696,8 +696,8 @@ static int __init i8k_init_hwmon(void)
 }
 
 struct i8k_config_data {
-       int fan_mult;
-       int fan_max;
+       uint fan_mult;
+       uint fan_max;
 };
 
 enum i8k_configs {



diff --git a/drivers/char/i8k.c b/drivers/char/i8k.c
index d6e8a26..6ad0872 100644
--- a/drivers/char/i8k.c
+++ b/drivers/char/i8k.c
@@ -6,6 +6,7 @@
  * Hwmon integration:
  * Copyright (C) 2011  Jean Delvare <[email protected]>
  * Copyright (C) 2013, 2014  Guenter Roeck <[email protected]>
+ * Copyright (C) 2014  Pali Rohár <[email protected]>
  *
  * 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);
@@ -276,6 +279,17 @@ static int i8k_get_fan_speed(int fan)
 }
 
 /*
+ * 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.
  */
 static int i8k_set_fan(int fan, int speed)
@@ -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;
 }
 

-- 
Pali Rohár
[email protected]

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