Bugs in dps310 Linux driver

["Andres Heinloo" <andres@gfz-potsdam.de>]

Hello,

I've been struggling with the dps310 driver, which gives incorrect 
pressure values and in particular different values than manufacturers 
code (https://github.com/Infineon/RaspberryPi_DPS).

I think I've found where the problem is. Firstly, there is a mistake 
in bit numbering at 
https://github.com/torvalds/linux/blob/857f1268a591147f7be7509f249dbb3aba6fc65c/drivers/iio/pressure/dps310.c#L51

According to datasheet, correct is:

#define  DPS310_INT_HL          BIT(7)
#define  DPS310_TMP_SHIFT_EN    BIT(3)
#define  DPS310_PRS_SHIFT_EN    BIT(2)
#define  DPS310_FIFO_EN         BIT(1)
#define  DPS310_SPI_EN          BIT(0)

Eg., the current code is using wrong bit (4) for DPS310_PRS_SHIFT_EN, 
which means that pressure shift is never enabled.

Secondly, there is a problem with overflows starting at 
https://github.com/torvalds/linux/blob/857f1268a591147f7be7509f249dbb3aba6fc65c/drivers/iio/pressure/dps310.c#L654

Since p is a 24-bit value,

nums[3] = p * p * p * (s64)data->c30;

can and does overflow.

Second overflow problem is at 
https://github.com/torvalds/linux/blob/857f1268a591147f7be7509f249dbb3aba6fc65c/drivers/iio/pressure/dps310.c#L684

In fact, I don't understand why 1000000000LL is needed. Since only 7 
values are summed, using 10LL should give the same precision.

Best regards,
Andres