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Message-ID: <aSn3PthKIvFAhDS6@smile.fi.intel.com>
Date: Fri, 28 Nov 2025 21:25:50 +0200
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Jorge Marques <gastmaier@...il.com>
Cc: Jorge Marques <jorge.marques@...log.com>,
Lars-Peter Clausen <lars@...afoo.de>,
Michael Hennerich <Michael.Hennerich@...log.com>,
Jonathan Cameron <jic23@...nel.org>,
David Lechner <dlechner@...libre.com>,
Nuno Sá <nuno.sa@...log.com>,
Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>,
Conor Dooley <conor+dt@...nel.org>,
Jonathan Corbet <corbet@....net>,
Linus Walleij <linus.walleij@...aro.org>,
Bartosz Golaszewski <brgl@...ev.pl>, linux-iio@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, linux-gpio@...r.kernel.org
Subject: Re: [PATCH v2 3/9] iio: adc: Add support for ad4062
On Fri, Nov 28, 2025 at 07:50:02PM +0100, Jorge Marques wrote:
> On Thu, Nov 27, 2025 at 10:58:24AM +0200, Andy Shevchenko wrote:
> > On Wed, Nov 26, 2025 at 12:40:00PM +0100, Jorge Marques wrote:
> > > On Mon, Nov 24, 2025 at 12:20:57PM +0200, Andy Shevchenko wrote:
> > > > On Mon, Nov 24, 2025 at 10:18:02AM +0100, Jorge Marques wrote:
Please, remove the context you are agree with or which has no need
to be answered, it helps to parse and reply.
...
> > > > > +static int ad4062_calc_sampling_frequency(int fosc, unsigned int n_avg)
> > > > > +{
> > > > > + /* See datasheet page 31 */
> > > > > + u64 duration = div_u64((u64)(n_avg - 1) * NSEC_PER_SEC, fosc) + AD4062_TCONV_NS;
> > > > > +
> > > > > + return DIV_ROUND_UP_ULL(NSEC_PER_SEC, duration);
> > > >
> > > > Why u64?
> > > >
> > > > The DIV_ROUND_UP_ULL() seems an overkill here. Or do you expect duration be
> > > > more than 4 billions?
> > > >
> > > This is necessary since at fosc 111 Hz and avg 4096 it does take longer
> > > than 4 seconds, even though I do timeout after 1 seconds in the raw
> > > acquisition.
> >
> > Values above NSEC_PER_SEC+1 do not make sense (it will return 0),
> > and that fits u32. Can you refactor to avoid 64-bit arithmetics?
>
> Ok, any frequency lower than 1 Hz does not make sense.
Depends on the cases, we have sub-Hz sensors or some other stuff.
So, "...does not make sense in _this_ case." That's what I implied.
> static int ad4062_calc_sampling_frequency(int fosc, unsigned int oversamp_ratio)
Shouldn't fosc be unsigned?
> {
> /* See datasheet page 31 */
It's fine, but better to add a formula here or more information about
the calculations done in the function.
> u32 period = NSEC_PER_SEC / fosc;
period_ns ?
(We usually add units to this kind of variables for better understanding
of the calculations)
> u32 n_avg = BIT(oversamp_ratio) - 1;
>
> /* Result is less than 1 Hz */
> if (n_avg >= fosc)
> return 1;
+ blank line.
> return NSEC_PER_SEC / (n_avg * period + AD4062_TCONV_NS);
> }
LGTM, thanks!
> > > > > +}
...
> > > static int ad4062_set_chan_calibscale(struct ad4062_state *st, int gain_int,
> > > int gain_frac)
> > > {
> > > u32 gain;
> > > int ret;
> > >
> > > if (gain_int < 0 || gain_frac < 0)
> > > return -EINVAL;
> > >
> > > gain = gain_int * MICRO + gain_frac;
> > > if (gain > 1999970)
> >
> > But this magic should be changed to what you explained to me
> > (as in 0xffff/0x8000 with the proper precision, and this
> > can be done in 32-bit space).
> >
> > Or even better
> >
> > if (gain_int < 0 || gain_int > 1)
> > return -EINVAL;
> >
> > if (gain_int == 1 && gain_frac > 0x7fff) // did I get this right?
> > return -EINVAL;
> gain_frac would be 999999 max, or 999970 for the limit that fits in the
> register after the math. I think > 1.999.970 is self explanatory.
On the place of unprepared reader this is a complete magic number without
scale, without understanding where it came from, etc.
So, can you define it as a derivative from the other constants and with
a comment perhaps?
> > > return -EINVAL;
> > >
> > > put_unaligned_be16(DIV_ROUND_CLOSEST_ULL((u64)gain * AD4062_MON_VAL_MIDDLE_POINT,
> > > MICRO),
> >
> > ...with temporary variable at minimum.
> >
> > But again, I still don't see the need for 64-bit space.
>
> Well, by dividing mon_val and micro values by a common divisor the
> operation fit in 32-bits:
>
> static int ad4062_set_chan_calibscale(struct ad4062_state *st, int gain_int,
> int gain_frac)
> {
/* Divide numerator and denumerator by known great common divider */
> const u32 mon_val = AD4062_MON_VAL_MIDDLE_POINT / 64;
> const u32 micro = MICRO / 64;
Yep, I suggested the same in another patch under review (not yours) for
the similar cases where we definitely may easily avoid overflow.
Alternatively you can use gcd().
> const u32 gain = gain_int * MICRO + gain_frac;
> int ret;
>
> if (gain_int < 0 || gain_frac < 0)
> return -EINVAL;
>
> if (gain > 1999970)
> return -EINVAL;
>
> put_unaligned_be16(DIV_ROUND_CLOSEST(gain * mon_val, micro), st->buf.bytes);
>
> ret = regmap_bulk_write(st->regmap, AD4062_REG_MON_VAL,
> &st->buf.be16, sizeof(st->buf.be16));
> if (ret)
> return ret;
>
> /* Enable scale if gain is not equal to one */
> return regmap_update_bits(st->regmap, AD4062_REG_ADC_CONFIG,
> AD4062_REG_ADC_CONFIG_SCALE_EN_MSK,
> FIELD_PREP(AD4062_REG_ADC_CONFIG_SCALE_EN_MSK,
> !(gain_int == 1 && gain_frac == 0)));
Btw, I think you can move this check up and save in a temporary variable which
might affect the binary size of the compiled object as accesses to the gain_int
and gain_frac will be grouped in the same place with potential of the reusing
the CPU register(s)..
> }
> > > st->buf.bytes);
> > >
> > > ret = regmap_bulk_write(st->regmap, AD4062_REG_MON_VAL,
> > > &st->buf.be16, sizeof(st->buf.be16));
> > > if (ret)
> > > return ret;
> > >
> > > /* Enable scale if gain is not equal to one */
> > > return regmap_update_bits(st->regmap, AD4062_REG_ADC_CONFIG,
> > > AD4062_REG_ADC_CONFIG_SCALE_EN_MSK,
> > > FIELD_PREP(AD4062_REG_ADC_CONFIG_SCALE_EN_MSK,
> > > !(gain_int == 1 && gain_frac == 0)));
> > > }
> > >
> > > To provide the enough resolution to compute every step (e.g., 0xFFFF and
> > > 0xFFFE) with the arbitrary user input.
--
With Best Regards,
Andy Shevchenko
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