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List:       linux-iio
Subject:    [bug report] staging:iio:sca3000 extract old event handling and move to poll for events from buffer
From:       Dan Carpenter <dan.carpenter () oracle ! com>
Date:       2021-05-28 12:00:52
Message-ID: YLDbdN688C0xBgMn () mwanda
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Hello Jonathan Cameron,

The patch 25888dc51163: "staging:iio:sca3000 extract old event
handling and move to poll for events from buffer" from May 18, 2011,
leads to the following static checker warning:

	drivers/iio/accel/sca3000.c:734 sca3000_read_raw()
	warn: no-op. '((*val) << 19) >> 19'

drivers/iio/accel/sca3000.c
   709  static int sca3000_read_raw(struct iio_dev *indio_dev,
   710                              struct iio_chan_spec const *chan,
   711                              int *val,
   712                              int *val2,
   713                              long mask)
   714  {
   715          struct sca3000_state *st = iio_priv(indio_dev);
   716          int ret;
   717          u8 address;
   718  
   719          switch (mask) {
   720          case IIO_CHAN_INFO_RAW:
   721                  mutex_lock(&st->lock);
   722                  if (chan->type == IIO_ACCEL) {
   723                          if (st->mo_det_use_count) {
   724                                  mutex_unlock(&st->lock);
   725                                  return -EBUSY;
   726                          }
   727                          address = sca3000_addresses[chan->address][0];
   728                          ret = sca3000_read_data_short(st, address, 2);
   729                          if (ret < 0) {
   730                                  mutex_unlock(&st->lock);
   731                                  return ret;
   732                          }
   733                          *val = (be16_to_cpup((__be16 *)st->rx) >> 3) & 0x1FFF;
   734                          *val = ((*val) << (sizeof(*val) * 8 - 13)) >>
                                                  ^^^^^^^^^^^^^^^^^^^^^^^
   735                                  (sizeof(*val) * 8 - 13);
                                        ^^^^^^^^^^^^^^^^^^^^^^^

This code works, but it relies on undefined behavior of left shift
overflow and it's very unsatisfying.  Pretty sure there is a UBSan
warning for this at runtime.

   736                  } else {
   737                          /* get the temperature when available */
   738                          ret = sca3000_read_data_short(st,
   739                                                        SCA3000_REG_TEMP_MSB_ADDR,
   740                                                        2);
   741                          if (ret < 0) {
   742                                  mutex_unlock(&st->lock);
   743                                  return ret;
   744                          }
   745                          *val = ((st->rx[0] & 0x3F) << 3) |
   746                                 ((st->rx[1] & 0xE0) >> 5);
   747                  }
   748                  mutex_unlock(&st->lock);
   749                  return IIO_VAL_INT;

regards,
dan carpenter
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