Re: [PATCH 2/5] power: supply: bd71828: Fix current direction

[Matti Vaittinen <mazziesaccount@gmail.com>]

On 12/08/2026 12:30, Andy Shevchenko wrote:
> On Wed, Aug 12, 2026 at 10:25:36AM +0200, Andreas Kemnade wrote:
>> On Wed, 12 Aug 2026 11:17:36 +0300
>> Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:
>>> On Wed, Aug 12, 2026 at 10:10:50AM +0200, Andreas Kemnade wrote:
>>>> On Mon, 10 Aug 2026 13:09:07 +0300
>>>> Matti Vaittinen <matti.vaittinen@linux.dev> wrote:
> 
> ...
> 
>>>> That code is complicated. What about a generic 16bit non_2complemented sign
>>>> to 2-complemented sign function/macro. Such would have prevented the error
>>>> in the first places. So &vals[i] = signbit_to_2complement(be16_to_cpu(tmp_curr), 15) * pwr->curr_factor
>>>
>>> Do you mean existing sign_extend32() from bitops.h?
>>>
>>
>> I don't think it does what is needed. Here we have
>>
>> 0000 0000 0000 0001 -> 1
>> Usually we have
>>
>> 1111 1111 1111 1111 -> -1
>>
>> but here
>>
>> 1000 0000 0000 0001 -> -1
> 
> I see, wouldn't this be then as simple as
> 
> 	sign = $REGVAL & BIT(15 /* sign bit */);
> 	if (sign)
> 		$REGVAL = sign - $REGVAL;

I find this more confusing than the current idea, which effectively is:

if (sign)
    val = val_without_sign * -1;
else
    val = val_without_sign (* 1);

(I can't straight away say if "$REGVAL = sign - $REGVAL;" yields same 
result.)

Yours,
   -- Matti

-- 
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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