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

On Wed, Aug 12, 2026 at 12:37:49PM +0300, Matti Vaittinen wrote:
> 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 <[email protected]> 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 <[email protected]> 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);

If you have other use for val_wo_sign, then you can even drop multiplication.

	val = sign ? -val_wo_sing: val_wo_sign;

More comprehensive view

	sign = $REGVAL & BIT(15 /* sign bit */);
	$REGVAL &= ~sign;
	val = sign ? -$REGVAL : $REGVAL;

-- 
With Best Regards,
Andy Shevchenko