linux-kernel - Re: [PATCH v10 6/7] iio: accel: adxl345: extend inactivity time for less than 1s

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Message-ID: <CAFXKEHb9Fbd_UOF90EumEtns82VPhYBrLZ=JtmhVJ4pJsT=q-g@mail.gmail.com>
Date: Mon, 23 Jun 2025 23:21:01 +0200
From: Lothar Rubusch <l.rubusch@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: lars@...afoo.de, Michael.Hennerich@...log.com, jic23@...nel.org, 
	dlechner@...libre.com, nuno.sa@...log.com, andy@...nel.org, corbet@....net, 
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-doc@...r.kernel.org, eraretuya@...il.com
Subject: Re: [PATCH v10 6/7] iio: accel: adxl345: extend inactivity time for
 less than 1s

Hi Andy,

This is a tricky one, I'll give some examples why (I think) the code
is needed as is.


On Mon, Jun 23, 2025 at 12:17 PM Andy Shevchenko
<andriy.shevchenko@...el.com> wrote:
>
> On Sun, Jun 22, 2025 at 03:50:09PM +0000, Lothar Rubusch wrote:
> > Inactivity and free-fall events are essentially the same type of sensor
> > events. Therefore, inactivity detection (normally set for periods between 1
> > and 255 seconds) can be extended for shorter durations to support free-fall
> > detection.
> >
> > For periods shorter than 1 second, the driver automatically configures the
> > threshold and duration using the free-fall register. For periods longer
> > than 1 second, it uses the inactivity threshold and duration using the
> > inactivity registers.
> >
> > When using the free-fall register, the link bit is not set, which means
> > auto-sleep cannot be enabled if activity detection is also active.
>
> ...
>
> > -static int adxl345_set_inact_time(struct adxl345_state *st, u32 val_s)
> > +static int adxl345_set_inact_time(struct adxl345_state *st, u32 val_int,
> > +                               u32 val_fract)
> >  {
> >       int max_boundary = U8_MAX;
> >       int min_boundary = 10;
> > -     unsigned int val = min(val_s, U8_MAX);
> > +     unsigned int val;
>
> You see, I even suggested splitting this assignment to begin with.
> The change will be clearer with that done.
>
> >       enum adxl345_odr odr;
> >       unsigned int regval;
> >       int ret;
> >
> > -     if (val == 0) {
> > +     if (val_int == 0 && val_fract == 0) {

The case for 0sec, 0.0 or setting "0" and fract will consequently be
"0". 0 is an invalid input for this period and sensor, so it will
default to an optimized period based on given ODR.

> > +             /* Generated inactivity time based on ODR */
> >               ret = regmap_read(st->regmap, ADXL345_REG_BW_RATE, &regval);
> >               if (ret)
> >                       return ret;
>
> >               odr = FIELD_GET(ADXL345_BW_RATE_MSK, regval);
> >               val = clamp(max_boundary - adxl345_odr_tbl[odr][0],
> >                           min_boundary, max_boundary);
> > +             st->inact_time_ms = MILLI * val;
> > +
> > +             /* Inactivity time in s */
> > +             return regmap_write(st->regmap, ADXL345_REG_TIME_INACT, val);
> > +     } else if (val_int == 0 && val_fract > 0) {
>
> val_fract check is not needed here.
>

Case for e.g. 0.123, numbers under 1s. This goes into the free-fall register.

> > +             /* time < 1s, free-fall */
> > +
> > +             /*
> > +              * Datasheet max. value is 255 * 5000 us = 1.275000 seconds.
> > +              *
> > +              * Recommended values between 100ms and 350ms (0x14 to 0x46)
> > +              */
> > +             st->inact_time_ms = DIV_ROUND_UP(val_fract, MILLI);
> > +
> > +             return regmap_write(st->regmap, ADXL345_REG_TIME_FF,
> > +                                 DIV_ROUND_CLOSEST(val_fract, 5));
> > +     } else if (val_int > 0) {
>
> if now is redundant here, right?
>

So, this will be 1s through 255s. Periods above 1sec. This goes into
the inactivity register.

> > +             /* Time >= 1s, inactivity */
> > +             st->inact_time_ms = MILLI * val_int;
> > +
> > +             return regmap_write(st->regmap, ADXL345_REG_TIME_INACT, val_int);
> >       }
> >
> > -     return regmap_write(st->regmap, ADXL345_REG_TIME_INACT, val);
> > +     /* Do not support negative or wrong input. */
> > +     return -EINVAL;
> >  }
>
> --
> With Best Regards,
> Andy Shevchenko
>
>