iio: pressure: ms5611: ms5611_prom_is_valid false negative bug

The ms5611 driver falsely rejects lots of MS5607-02BA03-50 chips
with "PROM integrity check failed" because it doesn't accept a prom crc
value of zero as legitimate.

According to the datasheet for this chip (and the manufacturer's
application note about the PROM CRC), none of the possible values for the
CRC are excluded - but the current code in ms5611_prom_is_valid() ends with

return crc_orig != 0x0000 && crc == crc_orig

Discussed with the driver author (Tomasz Duszynski) and he indicated that
at that time (2015) he was dealing with some faulty chip samples which
returned blank data under some circumstances and/or followed example code
which indicated CRC zero being bad.

As far as I can tell this exception should not be applied anymore; We've
got a few hundred custom boards here with this chip where large numbers
of the prom have a legitimate CRC value 0, and do work fine, but which the
current driver code wrongly rejects.

Signed-off-by: Alexander Zangerl <[email protected]>
Fixes: c064416 ("iio: pressure: add support for MS5611 pressure and temperature sensor")
Link: https://lore.kernel.org/r/[email protected]
Cc: <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>

Author: Alexander Zangerl

drivers/iio/pressure/ms5611_core.c

@@ -76,7 +76,7 @@ static bool ms5611_prom_is_valid(u16 *prom, size_t len)
 
 	crc = (crc >> 12) & 0x000F;
 
-	return crc_orig != 0x0000 && crc == crc_orig;
+	return crc == crc_orig;
 }
 
 static int ms5611_read_prom(struct iio_dev *indio_dev)