[bug report] iio: hrtimer: Allow sub Hz granularity

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

Hello Gwendal Grignou,

The patch dafcf4ed8392: "iio: hrtimer: Allow sub Hz granularity" from
Feb 25, 2021, leads to the following static checker warning:

	drivers/iio/trigger/iio-trig-hrtimer.c:68 iio_hrtimer_store_sampling_frequency()
	warn: assigned value is less than 'u32max'

drivers/iio/trigger/iio-trig-hrtimer.c
    49  static
    50  ssize_t iio_hrtimer_store_sampling_frequency(struct device *dev,
    51                                               struct device_attribute *attr,
    52                                               const char *buf, size_t len)
    53  {
    54          struct iio_trigger *trig = to_iio_trigger(dev);
    55          struct iio_hrtimer_info *info = iio_trigger_get_drvdata(trig);
    56          unsigned long long val;
    57          u64 period;
    58          int integer, fract, ret;
    59  
    60          ret = iio_str_to_fixpoint(buf, 100, &integer, &fract);
    61          if (ret)
    62                  return ret;
    63          if (integer < 0 || fract < 0)
    64                  return -ERANGE;
    65  
    66          val = fract + 1000 * integer;  /* mHz */
                      ^^^^^^^^^^^^^^^^^^^^^^
"fract" and "integer" are integers so the arithmatic will wrap instead
of going above UINT_MAX

    67  
    68          if (!val || val > UINT_MAX)
                            ^^^^^^^^^^^^^^
Unpossible!

    69                  return -EINVAL;
    70  
    71          info->sampling_frequency[0] = integer;  /* Hz */
    72          info->sampling_frequency[1] = fract * 1000;  /* uHz */
    73          period = PSEC_PER_SEC;
    74          do_div(period, val);
    75          info->period = period;  /* nS */
    76  
    77          return len;
    78  }

regards,
dan carpenter