hwmon: (nct6775) Do not accept force_id unless chip is found

Since commit 698a7c24a544 ("hwmon: (nct6775) Support two SuperIO chips
in the same system"), the driver supports two Super-IO chips. This has
the undesirable side effect that force_id always detects a second chip
at address 0xfff8, even if no chip exists at that address.

nct6775: Found NCT6793D or compatible chip at 0x4e:0xfff8

If no chip at all is found at a given SIO address, it does not make sense
to instantiate it. Limit force_id to only work if some chip is found,
that is if the chip ID returns a value other than 0xffff.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/nct6775.c b/drivers/hwmon/nct6775.c
index d087a8e00cf51abede39cc653341365a841b28d3..7859a30ce31ea31496fc1cae396b5b1be918b2ca 100644 (file)
--- a/drivers/hwmon/nct6775.c
+++ b/drivers/hwmon/nct6775.c
@@ -4232,11 +4232,11 @@ static int __init nct6775_find(int sioaddr, struct nct6775_sio_data *sio_data)
        if (err)
                return err;
 
-       if (force_id)
+       val = (superio_inb(sioaddr, SIO_REG_DEVID) << 8) |
+               superio_inb(sioaddr, SIO_REG_DEVID + 1);
+       if (force_id && val != 0xffff)
                val = force_id;
-       else
-               val = (superio_inb(sioaddr, SIO_REG_DEVID) << 8)
-                   | superio_inb(sioaddr, SIO_REG_DEVID + 1);
+
        switch (val & SIO_ID_MASK) {
        case SIO_NCT6106_ID:
                sio_data->kind = nct6106;