Re: [PATCH v7 1/6] iio: imu: st_lsm6dsx: Fix check for invalid samples from FIFO

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> On Wed,  4 Mar 2026 09:06:00 +0100
> Francesco Lavra <flavra@baylibre.com> wrote:
> 
> > The DRDY_MASK feature implemented in sensor chips marks gyroscope and
> > accelerometer invalid samples (i.e. samples that have been acquired during
> > the settling time of sensor filters) with the special values 0x7FFFh,
> > 0x7FFE, and 0x7FFD.
> > The driver checks FIFO samples against these special values in order to
> > discard invalid samples; however, it does the check regardless of the type
> > of samples being processed, whereas this feature is specific to gyroscope
> > and accelerometer data. This could cause valid samples to be discarded.
> > 
> > Fix the above check so that it takes into account the type of samples being
> > processed. To avoid casting to __le16 * when checking sample values, clean
> > up the type representation for data read from the FIFO.
> > 
> > Fixes: 960506ed2c69 ("iio: imu: st_lsm6dsx: enable drdy-mask if available")
> > Signed-off-by: Francesco Lavra <flavra@baylibre.com>
> Looks fine to me, but looking for a Lorenzo tag ideally given it's not
> a particularly trivial fix!
> 
> Jonathan

Hi Francesco,

thx for fixing this, I think the patch is fine, just a couple of nits inline if
you need to repost.

Regards,
Lorenzo

Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>

> > ---
> >  .../iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c    | 23 +++++++++++--------
> >  1 file changed, 14 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > index 5b28a3ffcc3d..a6ee2da5a06c 100644
> > --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_buffer.c
> > @@ -365,8 +365,6 @@ static inline int st_lsm6dsx_read_block(struct st_lsm6dsx_hw *hw, u8 addr,
> >  	return 0;
> >  }
> >  
> > -#define ST_LSM6DSX_IIO_BUFF_SIZE	(ALIGN(ST_LSM6DSX_SAMPLE_SIZE, \
> > -					       sizeof(s64)) + sizeof(s64))
> >  /**
> >   * st_lsm6dsx_read_fifo() - hw FIFO read routine
> >   * @hw: Pointer to instance of struct st_lsm6dsx_hw.
> > @@ -539,14 +537,14 @@ int st_lsm6dsx_read_fifo(struct st_lsm6dsx_hw *hw)
> >  #define ST_LSM6DSX_INVALID_SAMPLE	0x7ffd
> >  static int
> >  st_lsm6dsx_push_tagged_data(struct st_lsm6dsx_hw *hw, u8 tag,
> > -			    u8 *data, s64 ts)
> > +			    __le16 *data, s64 ts)
> >  {
> > -	s16 val = le16_to_cpu(*(__le16 *)data);
> >  	struct st_lsm6dsx_sensor *sensor;
> >  	struct iio_dev *iio_dev;
> >  
> >  	/* invalid sample during bootstrap phase */
> > -	if (val >= ST_LSM6DSX_INVALID_SAMPLE)
> > +	if ((tag == ST_LSM6DSX_GYRO_TAG || tag == ST_LSM6DSX_ACC_TAG) &&
> > +	    (s16)le16_to_cpup(data) >= ST_LSM6DSX_INVALID_SAMPLE)
> >  		return -EINVAL;

what about moving this check to a dedicated routine? Like
st_lsm6dsx_check_data() or similar?

> >  
> >  	/*
> > @@ -609,7 +607,13 @@ int st_lsm6dsx_read_tagged_fifo(struct st_lsm6dsx_hw *hw)
> >  	 * must be passed a buffer that is aligned to 8 bytes so
> >  	 * as to allow insertion of a naturally aligned timestamp.
> >  	 */
> > -	u8 iio_buff[ST_LSM6DSX_IIO_BUFF_SIZE] __aligned(8);
> > +	struct {
> > +		union {
> > +			__le16 data[3];
> > +			__le32 fifo_ts;
> > +		};
> > +		aligned_s64 timestamp;
> > +	} iio_buff = { };

you can get rid of space between brackets.

> >  	u8 tag;
> >  	bool reset_ts = false;
> >  	int i, err, read_len;
> > @@ -648,7 +652,7 @@ int st_lsm6dsx_read_tagged_fifo(struct st_lsm6dsx_hw *hw)
> >  
> >  		for (i = 0; i < pattern_len;
> >  		     i += ST_LSM6DSX_TAGGED_SAMPLE_SIZE) {
> > -			memcpy(iio_buff, &hw->buff[i + ST_LSM6DSX_TAG_SIZE],
> > +			memcpy(&iio_buff, &hw->buff[i + ST_LSM6DSX_TAG_SIZE],
> >  			       ST_LSM6DSX_SAMPLE_SIZE);
> >  
> >  			tag = hw->buff[i] >> 3;
> > @@ -659,7 +663,7 @@ int st_lsm6dsx_read_tagged_fifo(struct st_lsm6dsx_hw *hw)
> >  				 * B0 = ts[7:0], B1 = ts[15:8], B2 = ts[23:16],
> >  				 * B3 = ts[31:24]
> >  				 */
> > -				ts = le32_to_cpu(*((__le32 *)iio_buff));
> > +				ts = le32_to_cpu(iio_buff.fifo_ts);
> >  				/*
> >  				 * check if hw timestamp engine is going to
> >  				 * reset (the sensor generates an interrupt
> > @@ -670,7 +674,8 @@ int st_lsm6dsx_read_tagged_fifo(struct st_lsm6dsx_hw *hw)
> >  					reset_ts = true;
> >  				ts *= hw->ts_gain;
> >  			} else {
> > -				st_lsm6dsx_push_tagged_data(hw, tag, iio_buff,
> > +				st_lsm6dsx_push_tagged_data(hw, tag,
> > +							    iio_buff.data,
> >  							    ts);
> >  			}
> >  		}
> 

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