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

[Matti Vaittinen]

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@xxxxxxxxxxxxxxx> 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@xxxxxxxxx> 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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