Re: [PATCH 03/13] power: max17047_battery: The temp alert values are 8-bit 2's complement

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 14-04-17 17:09, Krzysztof Kozlowski wrote:
> On Fri, Apr 14, 2017 at 02:59:09PM +0200, Hans de Goede wrote:
>> The temp alert values are 8-bit 2's complement, so sign-extend them
>> before reporting them back to the caller.
>
> Are you sure that these are reported with sign bit? I couldn't find
> confirmation of this in datasheet.

From: MAX17047-MAX17050.pdf

"T ALRT Threshold Register (02h)
The T ALRT Threshold register sets upper and lower limits
that generate an ALRT pin interrupt if exceeded by the
Temperature register value. The upper 8 bits set the maxi-
mum value and the lower 8 bits set the minimum value.
Interrupt threshold limits are stored in two’s-complement
format"

And the reset default of 7F80h also hints at this,
as it is +127 for max -128 for min (aka temp based
alerts disabled).

Regards,

Hans


>
> Best regards,
> Krzysztof
>
>>
>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>> ---
>>  drivers/power/supply/max17042_battery.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/power/supply/max17042_battery.c b/drivers/power/supply/max17042_battery.c
>> index 790dfa9..a51b296 100644
>> --- a/drivers/power/supply/max17042_battery.c
>> +++ b/drivers/power/supply/max17042_battery.c
>> @@ -270,14 +270,14 @@ static int max17042_get_property(struct power_supply *psy,
>>  		if (ret < 0)
>>  			return ret;
>>  		/* LSB is Alert Minimum. In deci-centigrade */
>> -		val->intval = (data & 0xff) * 10;
>> +		val->intval = sign_extend32(data & 0xff, 7) * 10;
>>  		break;
>>  	case POWER_SUPPLY_PROP_TEMP_ALERT_MAX:
>>  		ret = regmap_read(map, MAX17042_TALRT_Th, &data);
>>  		if (ret < 0)
>>  			return ret;
>>  		/* MSB is Alert Maximum. In deci-centigrade */
>> -		val->intval = (data >> 8) * 10;
>> +		val->intval = sign_extend32(data >> 8, 7) * 10;
>>  		break;
>>  	case POWER_SUPPLY_PROP_TEMP_MIN:
>>  		val->intval = chip->pdata->temp_min;
>> --
>> 2.9.3
>>