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

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Message-ID: <10724132.nUPlyArG6x@radijator>
Date: Sat, 30 Aug 2025 15:03:47 +0200
From: Duje Mihanović <duje@...emihanovic.xyz>
To: David Lechner <dlechner@...libre.com>,
 Andy Shevchenko <andy.shevchenko@...il.com>
Cc: 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 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?

> > > +     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.

> > > +             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?

> > > +     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?

> > > +     const u8 config[] = {0xff, 0xfd, 0x1};
> > 
> > IIRC, IIO subsystem prefers spaces around the braces.
> > 
> >                         { 0xff, 0xfd, 0x1 };
> 
> Also make them fixed width, i.e. 0x01

I've replaced these with macros as David suggested.

> > > +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'?

Regards,
--
Duje