[lm-sensors] [PATCH v3 2/3] hwmon: (lm95241) Fix negative temperature results

[Jean Delvare]

Hi Guenter,

On Thu, 7 Jul 2011 13:42:44 -0700, Guenter Roeck wrote:
> Negative temperatures were returned in degrees C instead of milli-Degrees C.
> Also, negative temperatures were reported for remote temperature sensors even
> if the chip was configured for positive-only results.
> 
> Fix by detecting temperature modes, and by treating negative temperatures
> similar to positive temperatures, with appropriate sign extension.
> 
> Signed-off-by: Guenter Roeck <guenter.roeck at ericsson.com>
> ---
> Candidate for -stable.
> 
>  drivers/hwmon/lm95241.c |   20 ++++++++++++++------
>  1 files changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hwmon/lm95241.c b/drivers/hwmon/lm95241.c
> index 01c638e..ec02e30 100644
> --- a/drivers/hwmon/lm95241.c
> +++ b/drivers/hwmon/lm95241.c
> @@ -98,11 +98,16 @@ struct lm95241_data {
>  };
>  
>  /* Conversions */
> -static int TempFromReg(u8 val_h, u8 val_l)
> +static int temp_from_reg_signed(u8 val_h, u8 val_l)
>  {
> -	if (val_h & 0x80)
> -		return val_h - 0x100;
> -	return val_h * 1000 + val_l * 1000 / 256;
> +	s16 val_hl = (val_h << 8) | val_l;
> +	return val_hl * 1000 / 256;
> +}
> +
> +static int temp_from_reg_unsigned(u8 val_h, u8 val_l)
> +{
> +	u16 val_hl = (val_h << 8) | val_l;
> +	return val_hl * 1000 / 256;
>  }
>  
>  static struct lm95241_data *lm95241_update_device(struct device *dev)
> @@ -135,10 +140,13 @@ static ssize_t show_input(struct device *dev, struct device_attribute *attr,
>  			  char *buf)
>  {
>  	struct lm95241_data *data = lm95241_update_device(dev);
> +	int index = to_sensor_dev_attr(attr)->index;
>  
>  	return snprintf(buf, PAGE_SIZE - 1, "%d\n",
> -		TempFromReg(data->temp[to_sensor_dev_attr(attr)->index],
> -			    data->temp[to_sensor_dev_attr(attr)->index + 1]));
> +			!index || (data->config & index) ?

Hmm. This really should be:

+			!index || (data->config & (1 << (index / 2))) ?

It just _happens_ that (1 << (index / 2)) == index for index values 2
and 4, so your code works. But if we ever add support for a compatible
device with an extra temperature channel, it'll break. Not sure if the
rest of the driver code would properly cope with such a change anyway,
though.

Furthermore, I think that readability could be slightly improved by
changing "!index" to "index == 0", as this is neither an error
condition nor a boolean).

Readability could be improved even more with driver-wide changes but
this is obviously out-of-scope for this patch.

> +		temp_from_reg_signed(data->temp[index], data->temp[index + 1]) :
> +		temp_from_reg_unsigned(data->temp[index],
> +				       data->temp[index + 1]));
>  }
>  
>  static ssize_t show_type(struct device *dev, struct device_attribute *attr,

-- 
Jean Delvare