Function devm_regmap_init_i2c() returns an ERR_PTR on errors, and its return value should be checked before using. 

Function hmc5843_i2c_probe() in drivers\iio\magnetometer\hmc5843_i2c.c use the return value of devm_regmap_init_i2c() as an argument of hmc5843_common_probe without validation.

In addition, the hmc5843_common_probe() defined in drivers\iio\magnetometer\hmc5843_core.c as the following where the second parameter is used directly. Therefore, the return value of devm_regmap_init_i2c() is missing checked.

drivers\iio\magnetometer\hmc5843_i2c.c:
   60  {
   61  	return hmc5843_common_probe(&cli->dev,
   62: 			devm_regmap_init_i2c(cli, &hmc5843_i2c_regmap_config),
   63  			id->driver_data, id->name);
   64  }

drivers\iio\magnetometer\hmc5843_core.c
int hmc5843_common_probe(struct device *dev, struct regmap *regmap,
			 enum hmc5843_ids id, const char *name)
{
	struct hmc5843_data *data;
	struct iio_dev *indio_dev;
	int ret;

	indio_dev = devm_iio_device_alloc(dev, sizeof(*data));
	if (!indio_dev)
		return -ENOMEM;

	dev_set_drvdata(dev, indio_dev);

	/* default settings at probe */
	data = iio_priv(indio_dev);
	data->dev = dev;
	data->regmap = regmap;
	data->variant = &hmc5843_chip_info_tbl[id];
	mutex_init(&data->lock);

Here is the correct usage,

input\touchscreen\tsc2004.c:
   49  {
   50  	return tsc200x_probe(&i2c->dev, i2c->irq, &tsc2004_input_id,
   51: 			     devm_regmap_init_i2c(i2c, &tsc200x_regmap_config),
   52  			     tsc2004_cmd);
   53  }

drivers\input\touchscreen\tsc200x-core.c
int tsc200x_probe(struct device *dev, int irq, const struct input_id *tsc_id,
		  struct regmap *regmap,
		  int (*tsc200x_cmd)(struct device *dev, u8 cmd))
{
	struct tsc200x *ts;
	struct input_dev *input_dev;
	u32 x_plate_ohm;
	u32 esd_timeout;
	int error;

	if (irq <= 0) {
		dev_err(dev, "no irq\n");
		return -ENODEV;
	}

	if (IS_ERR(regmap))
		return PTR_ERR(regmap);