linux-kernel - Re: [PATCH 1/2] iio: adc: Add driver for Marvell 88PM886 PMIC ADC

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Message-ID: <CAHp75VcU-AbfRfMZUanV8eHb5oatQPhGS-ntyWuDFtUgKc-OLA@mail.gmail.com>
Date: Sat, 30 Aug 2025 17:53:48 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Duje Mihanović <duje@...emihanovic.xyz>
Cc: David Lechner <dlechner@...libre.com>, Jonathan Cameron <jic23@...nel.org>, 
	Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, Karel Balej <balejk@...fyz.cz>, Lee Jones <lee@...nel.org>, 
	David Wronek <david@...nlining.org>, phone-devel@...r.kernel.org, 
	~postmarketos/upstreaming@...ts.sr.ht, linux-kernel@...r.kernel.org, 
	linux-iio@...r.kernel.org
Subject: Re: [PATCH 1/2] iio: adc: Add driver for Marvell 88PM886 PMIC ADC

On Sat, Aug 30, 2025 at 4:04 PM Duje Mihanović <duje@...emihanovic.xyz> wrote:
> On Saturday, 30 August 2025 06:37:27 Central European Summer Time Andy Shevchenko wrote:
> > On Fri, Aug 29, 2025 at 2:41 AM David Lechner <dlechner@...libre.com> wrote:
> > > On 8/28/25 5:17 PM, Duje Mihanović wrote:

...

> > > +     if (adcnum < 0 || adcnum > 3)
> > > +             return -EINVAL;
> >
> > in_range()
>
> Not sure how relevant that check is anymore; in my current local
> version this can definitely only be called for one of the GPADCx
> channels. Should I drop it then?

Good point. Yes, we don't want a dead code in the kernel (or always
true / false conditionals).

...

> > > > +     for (int i = 0; i < 16; i++) {
> >
> > Why signed? What is the magic value here?
>
> No magic to my understanding, it's that the bias generator can output
> 16 different current levels.

The define it

#define ..._MAX_OUTPUT_CURRENT_LEVELS  16

...

> > > > +             ret = regmap_update_bits(*map, reg, 0xf, i);
> >
> > GENMASK() or even better to have a definitive constant.
>
> While at it, could
>
> > > +              *amp = 1 + i * 5;
>
> use a macro too?

This is something I haven't checked, dunno.

...

> > > > +     raw = gpadc_get_raw(iio, chan->channel);
> > > > +     if (raw < 0) {
> > > > +             ret = raw;
> > > > +             goto out;
> > > > +     }
> >
> > Instead just assign to ret and if okay, reassign to raw.
>
> I've refactored that function greatly since and now have:
>
> *val = gpadc_get_raw(iio, chan->channel);
> if (*val < 0)
>         return *val;
>
> Is assigning to *val immediately alright?

Only if it's not going to change anymore in this function.

...

> > > > +config 88PM886_GPADC
> > > > +     tristate "Marvell 88PM886 GPADC driver"
> > > > +     depends on MFD_88PM886_PMIC
> > > > +     default y
> >
> > Really? Why tristate then?
> > I would expect default MFD_88PM886_PMIC instead,
> >
> > > > +     help
> > > > +       Say Y here to enable support for the GPADC (General Purpose ADC)
> > > > +       found on the Marvell 88PM886 PMIC. The GPADC measures various
> > > > +       internal voltages and temperatures, including (but not limited to)
> > > > +       system, battery and USB.
> >
> > Please, add a line about the module name if one chooses 'm'. Or see
> > above — drop the "tristate" and explain why this driver may not be a
> > module in the commit message.
>
> 'default MFD_88PM886_PMIC' would make it y as that one is a bool. How
> about 'default m if MFD_88PM886_PMIC' or, since this already depends on
> _PMIC, 'default m'?

I didn't get it. Why? defaulting to MFD is okay, otherwise one needs
to explain 'y' (and even explicit 'm' choice) for the _leaf_ driver.

-- 
With Best Regards,
Andy Shevchenko