Re: [PATCH v3 06/15] iio: accel: adxl345: add single tap feature

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 13 Mar 2025 17:29:08 +0100
Lothar Rubusch <l.rubusch@gmail.com> wrote:

> Hi Jonathan,
> 
> I prepared, reorganized and tested a v4 patch set. Given that I see
> how busy you must be these days with current increased mail traffic
> just in IIO ML when I compare it to some years ago,
> I don't want to bother you too much.

Thanks!  It's a travel heavy month which always messes with finding
time for reviews.  Too much bored time on planes with not enough space
to open a laptop properly!

> Some particular doubts I will inline down below. If possible with your
> work flow and to avoid giving you extra work, I'd like to ask you to
> read the questions here, but to give your answers right to the
> v4 patch set (so, i.e. after having seen the current state of source).
> It also should make my points
> a bit clearer. Anyway, this is just my idea, since I'm always happy
> about any feedback!

I might reply there as well, but it's easy to put a few comments here.

> 
> On Sun, Mar 2, 2025 at 1:14 PM Jonathan Cameron <jic23@kernel.org> wrote:
> >
> > On Thu, 20 Feb 2025 10:42:25 +0000
> > Lothar Rubusch <l.rubusch@gmail.com> wrote:
> >  
> > > Add the single tap feature with a threshold in 62.5mg/LSB points and a
> > > scaled duration in us. Keep singletap threshold in regmap cache but
> > > the scaled value of duration in us as member variable.
> > >
> > > Both use IIO channels for individual enable of the x/y/z axis. Initializes
> > > threshold and duration with reasonable content. When an interrupt is
> > > caught it will be pushed to the according IIO channel.
> > >
> > > Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
> > > ---
> > >  drivers/iio/accel/adxl345_core.c | 364 ++++++++++++++++++++++++++++++-
> > >  1 file changed, 362 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
> > > index 0cee81bc1877..d05593c0d513 100644
> > > --- a/drivers/iio/accel/adxl345_core.c
> > > +++ b/drivers/iio/accel/adxl345_core.c
> > > @@ -8,6 +8,7 @@
> > >   */
> > >
> > >  #include <linux/bitfield.h>
> > > +#include <linux/bitops.h>
> > >  #include <linux/interrupt.h>
> > >  #include <linux/module.h>
> > >  #include <linux/property.h>
> > > @@ -17,6 +18,7 @@
> > >  #include <linux/iio/iio.h>
> > >  #include <linux/iio/sysfs.h>
> > >  #include <linux/iio/buffer.h>
> > > +#include <linux/iio/events.h>
> > >  #include <linux/iio/kfifo_buf.h>
> > >
> > >  #include "adxl345.h"
> > > @@ -31,6 +33,33 @@
> > >  #define ADXL345_INT1                 0
> > >  #define ADXL345_INT2                 1
> > >
> > > +#define ADXL345_REG_TAP_AXIS_MSK     GENMASK(2, 0)  
> > This is a bit confusing.  Here we have a mask for axis that
> > has 3 bits.  
> > > +
> > > +enum adxl345_axis {
> > > +     ADXL345_Z_EN = BIT(0),
> > > +     ADXL345_Y_EN = BIT(1),
> > > +     ADXL345_X_EN = BIT(2),
> > > +     /* Suppress double tap detection if value > tap threshold */
> > > +     ADXL345_TAP_SUPPRESS = BIT(3),  
> > and here an enum that is closely related with 4.  
> 
> I see your point. There are several registers used in the sensor for
> directions. A status register for tap and activity directions, and a
> activity/inactivity direction register. For Tap, direction enables are
> stored using the suppress bit in the fourth position. All those
> locations use actually four bit. Partly the upper four, partly the
> lower four. That's why I use here four bit for reading and writing.
> The locations 0, 1, 2 then can be used directly. Location 3 only
> applies to tap detection.
> 
> I'll keep this in v4 patches, and hope to understand you correctly
> that this is not a "real" issue?
I'd split the AXIS_MSK into two parts.  One with just the axes
(make it the | of the 3 separate bits) and another one with suppress bit.
I'm not sure an enum really helps. Maybe better to just have defines.


> > > +
> > > +static int adxl345_read_event_value(struct iio_dev *indio_dev,
> > > +                                 const struct iio_chan_spec *chan,
> > > +                                 enum iio_event_type type,
> > > +                                 enum iio_event_direction dir,
> > > +                                 enum iio_event_info info,
> > > +                                 int *val, int *val2)
> > > +{
> > > +     struct adxl345_state *st = iio_priv(indio_dev);
> > > +     unsigned int tap_threshold;
> > > +     int ret;
> > > +
> > > +     switch (type) {
> > > +     case IIO_EV_TYPE_GESTURE:
> > > +             switch (info) {
> > > +             case IIO_EV_INFO_VALUE:
> > > +                     /*
> > > +                      * The scale factor is 62.5mg/LSB (i.e. 0xFF = 16g) but
> > > +                      * not applied here.  
> >
> > Maybe say why.
> >  
> 
> Usually I did scaling for the time values. Time values is something I
> can understand someone
> rather wants to configure in corresponding time units, such as [ms],
> [us] or [s] rather than bit
> values. For [mg] values, franckly speaking, I imagine this is a bit overkill.
> 
> The threshold quite often is rather expect to be higher or lower,
> depending a bit on variation of
> the measurements. In the context of this rather "cheap" sensor, I
> guess I'm not putting up a
> seismic instrument, but rather generic tap detection, freefall or
> general activity in a general
> purpose context such as gaming, or the like. Let me know if this
> assumption here is too lazy.

Generally event values would be matched to scale of _RAW but for a
gesture, it is indeed a rather vague thing.  I'll take a look at 
the new code and think about this a bit.

Jonathan