hwmon/w83627ehf: Preserve speed reading when changing fan min

The w83627ehf driver changes the fan clock divider automatically when
a new min fan speed is set. It is supposed to preserve the fan speed
reading while doing so, bug doesn't really. Fix it.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>

1 files changed, 9 insertions, 4 deletions

diff --git a/drivers/hwmon/w83627ehf.c b/drivers/hwmon/w83627ehf.c
index 30a76404f0af..f4d850c71585 100644
--- a/drivers/hwmon/w83627ehf.c
+++ b/drivers/hwmon/w83627ehf.c
@@ -716,10 +716,15 @@ store_fan_min(struct device *dev, struct device_attribute *attr,
         /* Write both the fan clock divider (if it changed) and the new
            fan min (unconditionally) */
         if (new_div != data->fan_div[nr]) {
-                if (new_div > data->fan_div[nr])
-                        data->fan[nr] >>= (data->fan_div[nr] - new_div);
-                else
-                        data->fan[nr] <<= (new_div - data->fan_div[nr]);
+                /* Preserve the fan speed reading */
+                if (data->fan[nr] != 0xff) {
+                        if (new_div > data->fan_div[nr])
+                                data->fan[nr] >>= new_div - data->fan_div[nr];
+                        else if (data->fan[nr] & 0x80)
+                                data->fan[nr] = 0xff;
+                        else
+                                data->fan[nr] <<= data->fan_div[nr] - new_div;
+                }
 
                 dev_dbg(dev, "fan%u clock divider changed from %u to %u\n",
                         nr + 1, div_from_reg(data->fan_div[nr]),