hwmon: (it87) Prevent power-off on Shuttle SN68PT

based on commit 98dd22c3 upstream

On the Shuttle SN68PT, FAN_CTL2 is apparently not connected to a fan,
but to something else. One user has reported instant system power-off
when changing the PWM2 duty cycle, so we disable it.

I use the board name string as the trigger in case the same board is
ever used in other systems.

This closes lm-sensors ticket #2349:
pwmconfig causes a hard poweroff
http://www.lm-sensors.org/ticket/2349Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/hwmon/it87.c

@@ -46,6 +46,8 @@
 #include <linux/err.h>
 #include <linux/mutex.h>
 #include <linux/sysfs.h>
+#include <linux/string.h>
+#include <linux/dmi.h>
 #include <asm/io.h>
 
 #define DRVNAME "it87"
@@ -235,6 +237,8 @@ struct it87_sio_data {
 	enum chips type;
 	/* Values read from Super-I/O config space */
 	u8 vid_value;
+	/* Values set based on DMI strings */
+	u8 skip_pwm;
 };
 
 /* For each registered chip, we need to keep some data in memory.
@@ -952,6 +956,7 @@ static int __init it87_find(unsigned short *address,
 {
 	int err = -ENODEV;
 	u16 chip_type;
+	const char *board_vendor, *board_name;
 
 	superio_enter();
 	chip_type = force_id ? force_id : superio_inw(DEVID);
@@ -1009,6 +1014,25 @@ static int __init it87_find(unsigned short *address,
 			pr_info("it87: in7 is VCCH (+5V Stand-By)\n");
 	}
 
+	sio_data->skip_pwm = 0;
+	/* Disable specific features based on DMI strings */
+	board_vendor = dmi_get_system_info(DMI_BOARD_VENDOR);
+	board_name = dmi_get_system_info(DMI_BOARD_NAME);
+	if (board_vendor && board_name) {
+		if (strcmp(board_vendor, "nVIDIA") == 0
+		 && strcmp(board_name, "FN68PT") == 0) {
+			/* On the Shuttle SN68PT, FAN_CTL2 is apparently not
+			   connected to a fan, but to something else. One user
+			   has reported instant system power-off when changing
+			   the PWM2 duty cycle, so we disable it.
+			   I use the board name string as the trigger in case
+			   the same board is ever used in other systems. */
+			pr_info("it87: Disabling pwm2 due to "
+				"hardware constraints\n");
+			sio_data->skip_pwm = (1 << 1);
+		}
+	}
+
 exit:
 	superio_exit();
 	return err;
@@ -1156,23 +1180,26 @@ static int __devinit it87_probe(struct platform_device *pdev)
 	if (enable_pwm_interface) {
 		if ((err = device_create_file(dev,
 		     &sensor_dev_attr_pwm1_enable.dev_attr))
-		 || (err = device_create_file(dev,
-		     &sensor_dev_attr_pwm2_enable.dev_attr))
 		 || (err = device_create_file(dev,
 		     &sensor_dev_attr_pwm3_enable.dev_attr))
 		 || (err = device_create_file(dev,
 		     &sensor_dev_attr_pwm1.dev_attr))
-		 || (err = device_create_file(dev,
-		     &sensor_dev_attr_pwm2.dev_attr))
 		 || (err = device_create_file(dev,
 		     &sensor_dev_attr_pwm3.dev_attr))
 		 || (err = device_create_file(dev,
 		     &dev_attr_pwm1_freq))
-		 || (err = device_create_file(dev,
-		     &dev_attr_pwm2_freq))
 		 || (err = device_create_file(dev,
 		     &dev_attr_pwm3_freq)))
 			goto ERROR4;
+		if (!(sio_data->skip_pwm & (1 << 1))) {
+			if ((err = device_create_file(dev,
+			     &sensor_dev_attr_pwm2_enable.dev_attr))
+			 || (err = device_create_file(dev,
+			     &sensor_dev_attr_pwm2.dev_attr))
+			 || (err = device_create_file(dev,
+			     &dev_attr_pwm2_freq)))
+				goto ERROR4;
+		}
 	}
 
 	if (data->type == it8712 || data->type == it8716