LIS2DUX12/LIS2DUXS12 driver create badly named event files

Hi, I'm using LIS2DUX12 accelerometer in a Linux environment with kernel version 5.10 and I'm testing event monitoring with iio_event_monitor tool. I managed to verify the functionality of a few events (TAP, DTAP, FF and MLC) but I couldn't test the behavior of the SIGN_MOTION event because I'm having a hard time trying to enable that event from C code. This is because the file responsible to track the event enable/disable status has a particularly bad name: in my case it is in_???'L0_thresh_rising_en. This made me realize that a few other event files were also incorrect because they are named like in_(null)0_thresh_rising_en.

So I decided to take a look inside the kernel and the driver to better understand what is going on and I found out that the driver is using custom enum type values to initialize the structure struct iio_chan_spec of these sensor.

/* stm_iio_types.h */
/* Linux IIO driver custom types */
enum {
    STM_IIO_LAST = 0x3f,
    STM_IIO_SIGN_MOTION = STM_IIO_LAST - 6,
    STM_IIO_STEP_COUNTER = STM_IIO_LAST - 5,
    STM_IIO_TILT = STM_IIO_LAST - 4,
    STM_IIO_TAP = STM_IIO_LAST - 3,
    STM_IIO_TAP_TAP = STM_IIO_LAST - 2,
    STM_IIO_WRIST_TILT_GESTURE = STM_IIO_LAST - 1,
    STM_IIO_GESTURE = STM_IIO_LAST,
};

/* st_lis2duxs12.h */
#define ST_LIS2DUXS12_EVENT_CHANNEL(ctype, etype)   \
{                           \
    .type = ctype,                  \
    .modified = 0,                  \
    .scan_index = -1,               \
    .indexed = -1,                  \
    .event_spec = &st_lis2duxs12_##etype##_event,   \
    .num_event_specs = 1,               \
}

/* st_lis2duxs12_basicfunc.c */
static const struct iio_chan_spec st_lis2duxs12_ff_channels[] = {
    ST_LIS2DUXS12_EVENT_CHANNEL(STM_IIO_GESTURE, thr),
    IIO_CHAN_SOFT_TIMESTAMP(1),
};
static const struct iio_chan_spec st_lis2duxs12_tap_channels[] = {
    ST_LIS2DUXS12_EVENT_CHANNEL(STM_IIO_TAP, thr),
    IIO_CHAN_SOFT_TIMESTAMP(1),
};
static const struct iio_chan_spec st_lis2duxs12_dtap_channels[] = {
    ST_LIS2DUXS12_EVENT_CHANNEL(STM_IIO_TAP_TAP, thr),
    IIO_CHAN_SOFT_TIMESTAMP(1),
};
static const struct iio_chan_spec st_lis2duxs12_ttap_channels[] = {
    ST_LIS2DUXS12_EVENT_CHANNEL(STM_IIO_GESTURE, thr),
    IIO_CHAN_SOFT_TIMESTAMP(1),
};

For my understanding, this is a problem because when the kernel generates the event names for these sensors/devices, it tries to get a char pointer from the iio_chan_type_name_spec[] variable that has only IIO_MASSCONCENTRATION (=34) items which is less than the first STM custom type STM_IIO_SIGN_MOTION (=57). So our index/type is out of bounds.

/* industrial-core.c */
static const char * const iio_chan_type_name_spec[] = {
    [IIO_VOLTAGE] = "voltage",
    [IIO_CURRENT] = "current",
    [IIO_POWER] = "power",
    [IIO_ACCEL] = "accel",
    [IIO_ANGL_VEL] = "anglvel",
    [IIO_MAGN] = "magn",
    [IIO_LIGHT] = "illuminance",
    [IIO_INTENSITY] = "intensity",
    [IIO_PROXIMITY] = "proximity",
    [IIO_TEMP] = "temp",
    [IIO_INCLI] = "incli",
    [IIO_ROT] = "rot",
    [IIO_ANGL] = "angl",
    [IIO_TIMESTAMP] = "timestamp",
    [IIO_CAPACITANCE] = "capacitance",
    [IIO_ALTVOLTAGE] = "altvoltage",
    [IIO_CCT] = "cct",
    [IIO_PRESSURE] = "pressure",
    [IIO_HUMIDITYRELATIVE] = "humidityrelative",
    [IIO_ACTIVITY] = "activity",
    [IIO_STEPS] = "steps",
    [IIO_ENERGY] = "energy",
    [IIO_DISTANCE] = "distance",
    [IIO_VELOCITY] = "velocity",
    [IIO_CONCENTRATION] = "concentration",
    [IIO_RESISTANCE] = "resistance",
    [IIO_PH] = "ph",
    [IIO_UVINDEX] = "uvindex",
    [IIO_ELECTRICALCONDUCTIVITY] = "electricalconductivity",
    [IIO_COUNT] = "count",
    [IIO_INDEX] = "index",
    [IIO_GRAVITY]  = "gravity",
    [IIO_POSITIONRELATIVE]  = "positionrelative",
    [IIO_PHASE] = "phase",
    [IIO_MASSCONCENTRATION] = "massconcentration",
};

I think this is the point where the empty string messes things up:

/* industrial-core.c */
/* int __iio_device_attr_init() */
case IIO_SEPARATE:
    if (chan->indexed)
        name = kasprintf(GFP_KERNEL, "%s_%s%d_%s",
                iio_direction[chan->output],
                iio_chan_type_name_spec[chan->type],
                chan->channel,
                full_postfix);

Am I understanding this behavior correctly? How can we fix this?

Thanks

STMicroelectronics / st-mems-android-linux-drivers-iio

LIS2DUX12/LIS2DUXS12 driver create badly named event files #20