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

[Armin Wolf <W_Armin@xxxxxx>]

commit c0d79987a0d82671bff374c07f2201f9bdf4aaa2 upstream.

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().

This patch was originally a performance optimization, but it turned
out a user with a buggy machine requires this patch since it also
fixes error reporting when i8k_get_fan_status fails.
https://github.com/lm-sensors/lm-sensors/pull/383

Tested on a Dell Inspiron 3505.

Cc: <stable@xxxxxxxxxxxxxxx> # 5.15.x
Signed-off-by: Armin Wolf <W_Armin@xxxxxx>
---
 drivers/hwmon/dell-smm-hwmon.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index 47fce97996de..9cb1c3588038 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -326,7 +326,7 @@ 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)
 {
@@ -338,7 +338,7 @@ 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)
@@ -452,7 +452,7 @@ 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:
--
2.30.2