hwmon: (pmbus/max31785) check for partial i2c_transfer in read_long_data

i2c_transfer() returns the number of messages successfully
transferred, not only a negative errno on failure. When called with
two messages (write command byte followed by a read of the 4-byte
response), a return value of 1 means the command write succeeded but
the read did not complete. In that case, rspbuf remains uninitialized
and must not be interpreted as valid data.

Treat any return value other than ARRAY_SIZE(msg) as an error, and
return -EIO for partial completion. Also return 0 on success instead
of the message count, since the caller only needs to distinguish
success from failure.

Signed-off-by: Sanman Pradhan <psanman@juniper.net>
Link: https://lore.kernel.org/r/20260321181052.27129-4-sanman.pradhan@hpe.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/pmbus/max31785.c b/drivers/hwmon/pmbus/max31785.c
index 260aa8fb50f13f5dc3f5e74a4a058b9a2243e202..3caa76bcbeb5ead96d02050b32b7eb02c14d250c 100644 (file)
--- a/drivers/hwmon/pmbus/max31785.c
+++ b/drivers/hwmon/pmbus/max31785.c
@@ -141,13 +141,13 @@ static int max31785_read_long_data(struct i2c_client *client, int page,
         */
        pmbus_update_ts(client, 0);
 
-       if (rc < 0)
-               return rc;
+       if (rc != ARRAY_SIZE(msg))
+               return rc < 0 ? rc : -EIO;
 
        *data = (rspbuf[0] << (0 * 8)) | (rspbuf[1] << (1 * 8)) |
                (rspbuf[2] << (2 * 8)) | (rspbuf[3] << (3 * 8));
 
-       return rc;
+       return 0;
 }
 
 static int max31785_get_pwm(struct i2c_client *client, int page)