linux-kernel - Re: [PATCH v9 05/11] iio: accel: adxl345: simplify reading the FIFO

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Message-ID: <CAFXKEHaGk5NZ4dT9xLkAfirn974P9miwjs=5N+PTqJ2x00QOiA@mail.gmail.com>
Date: Mon, 16 Jun 2025 00:14:47 +0200
From: Lothar Rubusch <l.rubusch@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: lars@...afoo.de, Michael.Hennerich@...log.com, 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 v9 05/11] iio: accel: adxl345: simplify reading the FIFO

Hi Jonathan,

On Sat, Jun 14, 2025 at 3:47 PM Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Tue, 10 Jun 2025 21:59:27 +0000
> Lothar Rubusch <l.rubusch@...il.com> wrote:
>
> > Bulk reading from the FIFO can be simplified. Remove unnecessary
> > variables and simplify reading sets of x-, y- and z-axis measurements.
> >
> > This is a refactoring change and should not impact functionality.
> >
> > Signed-off-by: Lothar Rubusch <l.rubusch@...il.com>
> > ---
> >  drivers/iio/accel/adxl345_core.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
> > index 18c625d323ba..dcfbfe4cac0f 100644
> > --- a/drivers/iio/accel/adxl345_core.c
> > +++ b/drivers/iio/accel/adxl345_core.c
> > @@ -884,15 +884,13 @@ static int adxl345_get_samples(struct adxl345_state *st)
> >   */
> >  static int adxl345_fifo_transfer(struct adxl345_state *st, int samples)
> >  {
> > -     size_t count;
> >       int i, ret = 0;
> >
> > -     /* count is the 3x the fifo_buf element size, hence 6B */
> > -     count = sizeof(st->fifo_buf[0]) * ADXL345_DIRS;
> >       for (i = 0; i < samples; i++) {
> >               /* read 3x 2 byte elements from base address into next fifo_buf position */
> >               ret = regmap_bulk_read(st->regmap, ADXL345_REG_XYZ_BASE,
> > -                                    st->fifo_buf + (i * count / 2), count);
> > +                                    st->fifo_buf + (i * ADXL345_DIRS),
> > +                                    2 * ADXL345_DIRS);
>                                        sizeof(st->fifo_buf[0]) * ADXL345_DIRS);
>
> As it's not locally obvious where that 2 comes from.

Hm, I left the comment some lines above: "read 3x 2 byte elements from
base address into next fifo_buf position" - so, the 2 comes from the 2
bytes. 3x because of the 3-axis sensor, so 3 axis times 2 bytes. How
can I improve it? The patch is just a simplification, removing that
unnecessary count variable.

>
> >               if (ret)
> >                       return ret;
> >
>