linux-kernel - Re: [PATCH 1/2] power: supply: Add support for RN5T618/RC5T619 charger and fuel gauge

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Message-ID: <20200827071019.7022301c@kemnade.info>
Date:   Thu, 27 Aug 2020 07:10:19 +0200
From:   Andreas Kemnade <andreas@...nade.info>
To:     Sebastian Reichel <sebastian.reichel@...labora.com>
Cc:     lee.jones@...aro.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, b.galvani@...il.com, phh@....me,
        letux-kernel@...nphoenux.org
Subject: Re: [PATCH 1/2] power: supply: Add support for RN5T618/RC5T619
 charger and fuel gauge

Hi,

On Wed, 26 Aug 2020 23:59:50 +0200
Sebastian Reichel <sebastian.reichel@...labora.com> wrote:

> Hi,
> 
> On Wed, Aug 26, 2020 at 08:28:34PM +0200, Andreas Kemnade wrote:
> > On Wed, 26 Aug 2020 19:48:17 +0200
> > Sebastian Reichel <sebastian.reichel@...labora.com> wrote:  
> > > On Sat, Aug 15, 2020 at 06:56:09PM +0200, Andreas Kemnade wrote:  
> > > > [...]
> > > > +static int rn5t618_battery_current_now(struct rn5t618_power_info *info,
> > > > +				       union power_supply_propval *val)
> > > > +{
> > > > +	u16 res;
> > > > +	int ret;
> > > > +
> > > > +	ret = rn5t618_battery_read_doublereg(info, RN5T618_CC_AVEREG1, &res);
> > > > +	if (ret)
> > > > +		return ret;
> > > > +
> > > > +	val->intval = res;
> > > > +	/* 2's complement */
> > > > +	if (val->intval & (1 << 13))
> > > > +		val->intval = val->intval - (1 << 14);  
> 
> Btw. I think sign_extend32() can be used here?
> 
> > > > +	/* negate current to be positive when discharging */
> > > > +	val->intval *= -1000;    
> > > 
> > > mh, the sign is not documented (which should be fixed). At least
> > > sbs-battery does it the other way around (negative current when
> > > discharging, positive otherwise). Some drivers do not support
> > > signed current and always report positive values (e.g. ACPI driver).
> > > 
> > > What did you use as reference for swapping the sign?
> > >   
> > Well, I have searched for documentation, found nothing and used the
> > bq27xxx driver as reference  which I am used to from the GTA04/GTA02,
> > so things behave equal. That are the devices where a was most
> > intensively looking at those values.
> > I thought that there would be some unwritten rule about that.  
> 
> The mess is mostly due to lacking reviewing from my side
> (and possibly my predecessors). I just went through a dozen of
> drivers and it looks like most either do not support signed current
> (and use negative values as error code :() or use negative current
> for discharge. I could not find any other driver using negative
> numbers for charging. I think it's best to negative = discharge as
> official correct value and will send an update patch for the
> documentation later.
> 
ok, I will remove that sign-change and keep/update the comment
so that you know that the driver does it the official way
and send a v2 with the other things you mentioned.

Regards,
Andreas

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