Re: [PATCH v3 12/19] hwmon: (mr75203) fix voltage equation for negative source input

Farber, Eliav
2022-09-01T12:48:25Z

On 8/31/2022 3:04 PM, Andy Shevchenko wrote:
> On Tue, Aug 30, 2022 at 07:22:05PM +0000, Eliav Farber wrote:
>> According to Moortec Embedded Voltage Monitor (MEVM) series 3 data
>> sheet,
>> the minimum input signal is -100mv and maximum input signal is +1000mv.
>> When n was small enough, such that PVT_N_CONST * n < PVT_R_CONST it
>> resulted in n overflowing to a very large number (since n is u32 type).
>>
>> This change fixes the problem by casting n to long and replacing shift
>> right with div operation.
>
> Fixes tag?

For v4 I modified the commit message to (hopefully) be more
understandable:

"
According to Moortec Embedded Voltage Monitor (MEVM) series 3 data
sheet, the minimum input signal is -100mv and maximum input signal
is +1000mv.

On 64 bit machines sizeof(u32) = 4 and sizeof(long) = 8.
So when measuring a negative input and n is small enough, such that
PVT_N_CONST * n < PVT_R_CONST, it results in n overflowing to a very
large number which is not negative (because 4 MSB bytes of val are 0).

This change fixes the sign problem and supports negative values by
casting n to long and replacing shift right with div operation.
"

> ...
>
>>               n &= SAMPLE_DATA_MSK;
>> +
>
> Unrelated change.

Removed.

--
Thanks, Eliav