hwmon: (dell-smm) Speed up setting of fan speed

When setting the fan speed, i8k_set_fan() calls i8k_get_fan_status(),
causing an unnecessary SMM call since from the two users of this
function, only i8k_ioctl_unlocked() needs to know the new fan status
while dell_smm_write() ignores the new fan status.
Since SMM calls can be very slow while also making error reporting
difficult for dell_smm_write(), remove the function call from
i8k_set_fan() and call it separately in i8k_ioctl_unlocked().

Tested on a Dell Inspiron 3505.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Pali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20211021190531.17379-6-W_Armin@gmx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Author: Wer-Wolf

drivers/hwmon/dell-smm-hwmon.c

@@ -327,7 +327,7 @@ static int i8k_enable_fan_auto_mode(const struct dell_smm_data *data, bool enabl
 }
 
 /*
- * Set the fan speed (off, low, high). Returns the new fan status.
+ * Set the fan speed (off, low, high, ...).
  */
 static int i8k_set_fan(const struct dell_smm_data *data, int fan, int speed)
 {
@@ -339,7 +339,7 @@ static int i8k_set_fan(const struct dell_smm_data *data, int fan, int speed)
 	speed = (speed < 0) ? 0 : ((speed > data->i8k_fan_max) ? data->i8k_fan_max : speed);
 	regs.ebx = (fan & 0xff) | (speed << 8);
 
-	return i8k_smm(&regs) ? : i8k_get_fan_status(data, fan);
+	return i8k_smm(&regs);
 }
 
 static int __init i8k_get_temp_type(int sensor)
@@ -453,7 +453,7 @@ static int
 i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd, unsigned long arg)
 {
 	int val = 0;
-	int speed;
+	int speed, err;
 	unsigned char buff[16];
 	int __user *argp = (int __user *)arg;
 
@@ -513,7 +513,11 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
 		if (copy_from_user(&speed, argp + 1, sizeof(int)))
 			return -EFAULT;
 
-		val = i8k_set_fan(data, val, speed);
+		err = i8k_set_fan(data, val, speed);
+		if (err < 0)
+			return err;
+
+		val = i8k_get_fan_status(data, val);
 		break;
 
 	default: