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

[Jonathan Cameron <jic23@kernel.org>]

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
> ---
>  .../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;
>  
>  	/*
> @@ -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 = { };
>  	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);
>  			}
>  		}