linux-kernel - Re: [PATCH 2/3] iio: imu: st_lsm6dsx: set FIFO ODR for accelerometer and magnetometer only

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Message-ID: <338c098efe0d22aa27d0713fba449e75c4355fc4.camel@baylibre.com>
Date: Mon, 12 Jan 2026 18:37:54 +0100
From: Francesco Lavra <flavra@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>, David Lechner
 <dlechner@...libre.com>,  Nuno Sá <nuno.sa@...log.com>,
 Andy Shevchenko <andy@...nel.org>,  linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] iio: imu: st_lsm6dsx: set FIFO ODR for
 accelerometer and magnetometer only

On Sun, 2026-01-11 at 16:26 +0000, Jonathan Cameron wrote:
> On Sun, 11 Jan 2026 16:23:51 +0000
> Jonathan Cameron <jic23@...nel.org> wrote:
> 
> > On Fri,  9 Jan 2026 19:15:27 +0100
> > Francesco Lavra <flavra@...libre.com> wrote:
> > 
> > > The st_lsm6dsx_set_fifo_odr() function, which is called when enabling
> > > and
> > > disabling the hardware FIFO, checks the contents of the hw->settings-
> > > >batch
> > > array at index sensor->id, and then sets the current ODR value in
> > > sensor
> > > registers that depend on whether the register address is set in the
> > > above
> > > array element. This logic is valid for internal sensors only, i.e.
> > > the
> > > accelerometer and magnetometer; however, since commit c91c1c844ebd

Oops: s/magnetometer/gyroscope/ (will fix this in the next iteration)

> > > ("iio:
> > > imu: st_lsm6dsx: add i2c embedded controller support"), this function
> > > is
> > > called also when configuring the hardware FIFO for external sensors
> > > (i.e.
> > > sensors accessed through the sensor hub functionality), which can
> > > result in
> > > unrelated device registers being written.
> > > 
> > > Add a check to the beginning of st_lsm6dsx_set_fifo_odr() so that it
> > > does
> > > not touch any registers unless it is called for internal sensors.
> > > 
> > > Fixes: c91c1c844ebd ("iio: imu: st_lsm6dsx: add i2c embedded
> > > controller support")
> > > Signed-off-by: Francesco Lavra <flavra@...libre.com>
> > This seems fine to me. Ideally it would have been first patch in the
> > series
> > as this is one we want to backport.  I'll leave it on list little while
> > though to see if Lorenzo or anyone else has time to take a look.
> > 
> One thing...
> 
> > Thanks,
> > 
> > Jonathan
> > 
> > 
> > > ---
> > >  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > > b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > > index 5ac45e6230b5..9db48e835d4f 100644
> > > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > > @@ -225,6 +225,9 @@ static int st_lsm6dsx_set_fifo_odr(struct
> > > st_lsm6dsx_sensor *sensor,
> > >         const struct st_lsm6dsx_reg *batch_reg;
> > >         u8 data;
> > >  
> > > +       /* Only accel and gyro have batch registers. */
> 
> It's true we can't use the batch register, but not clear from this
> comment
> that the else path below is inappropriate.  Is it the absence of patch
> register
> or just that the set_fifo_odr is meaningless for other sensors that
> matters?
> I think this comment needs to provide more detail.

The set_fifo_odr is meaningless for external sensors, so the else path
below is also inappropriate for external sensors; I will amend the comment
to clarify that only internal sensors have a FIFO ODR configuration
register.

> > > +       if (sensor->id >= ARRAY_SIZE(hw->settings->batch))
> > > +               return 0;
> > >         batch_reg = &hw->settings->batch[sensor->id];
> > >         if (batch_reg->addr) {
> > >                 int val;


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