[bug report] iio: accel: bma400: Add support for single and double tap events

[Dan Carpenter <dan.carpenter@oracle.com>]

Hello Jagath Jog J,

The patch 961db2da159d: "iio: accel: bma400: Add support for single
and double tap events" from Aug 31, 2022, leads to the following
Smatch static checker warning:

	drivers/iio/accel/bma400_core.c:1287 bma400_tap_event_en()
	error: uninitialized symbol 'field_value'.

drivers/iio/accel/bma400_core.c
    1242 static int bma400_tap_event_en(struct bma400_data *data,
    1243                                enum iio_event_direction dir, int state)
    1244 {
    1245         unsigned int mask, field_value;
                                    ^^^^^^^^^^^^
This is uninitialized.

    1246         int ret;
    1247 
    1248         /*
    1249          * Tap interrupts can be configured only in normal mode.
    1250          * See table in section 4.3 "Power modes - performance modes" of
    1251          * datasheet v1.2.
    1252          */
    1253         if (data->power_mode != POWER_MODE_NORMAL)
    1254                 return -EINVAL;
    1255 
    1256         /*
    1257          * Tap interrupts are operating with a data rate of 200Hz.
    1258          * See section 4.7 "Tap sensing interrupt" in datasheet v1.2.
    1259          */
    1260         if (data->sample_freq.hz != 200 && state) {
    1261                 dev_err(data->dev, "Invalid data rate for tap interrupts.\n");
    1262                 return -EINVAL;
    1263         }
    1264 
    1265         ret = regmap_update_bits(data->regmap, BMA400_INT12_MAP_REG,
    1266                                  BMA400_S_TAP_MSK,
    1267                                  FIELD_PREP(BMA400_S_TAP_MSK, state));
    1268         if (ret)
    1269                 return ret;
    1270 
    1271         switch (dir) {
    1272         case IIO_EV_DIR_SINGLETAP:
    1273                 mask = BMA400_S_TAP_MSK;
    1274                 set_mask_bits(&field_value, BMA400_S_TAP_MSK,
                                       ^^^^^^^^^^^^
Smatch ought to print a warning here but these macros use a bunch of
*(&(*(&field_value))) permutations that confuse Smatch.  Smatch does
not print a warning if you're just taking the address of a variable.

This initializes BIT(3)?  I believe that KMSan will detect this as a bug
an issue a warning here.

    1275                               FIELD_PREP(BMA400_S_TAP_MSK, state));
    1276                 break;
    1277         case IIO_EV_DIR_DOUBLETAP:
    1278                 mask = BMA400_D_TAP_MSK;
    1279                 set_mask_bits(&field_value, BMA400_D_TAP_MSK,
    1280                               FIELD_PREP(BMA400_D_TAP_MSK, state));
    1281                 break;
    1282         default:
    1283                 return -EINVAL;
    1284         }
    1285 
    1286         ret = regmap_update_bits(data->regmap, BMA400_INT_CONFIG1_REG, mask,
--> 1287                                  field_value);

This uses BIT(3).  The function only cares about BIT(3) but the other
bits are uninitialized.

    1288         if (ret)
    1289                 return ret;
    1290 
    1291         set_mask_bits(&data->tap_event_en_bitmask, mask, field_value);
    1292 
    1293         return 0;
    1294 }

regards,
dan carpenter