On Mon, 06 Mar 2023 22:15:15 +0100 "Andres Heinloo" <andres@xxxxxxxxxxxxxx> wrote: > On Sun, 05 Mar 2023 03:05:01 +0100 > "Andres Heinloo" <andres@xxxxxxxxxxxxxx> wrote: > > On Sat, 4 Mar 2023 17:06:20 +0000 > > Jonathan Cameron <jic23@xxxxxxxxxx> wrote: > >> On Fri, 03 Mar 2023 12:10:00 +0100 > >> "Andres Heinloo" <andres@xxxxxxxxxxxxxx> wrote: > >> > >>> 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. > >> > >> Checking the datasheet, seems like you are right. > >> https://www.infineon.com/dgdl/Infineon-DPS310-DataSheet-v01_02-EN.pdf?fileId=5546d462576f34750157750826c42242 > >> Section 7: > >> Though that's not the only bit that is wrong. Looks like FIFO > >>enable is as well. > >> So any fix should deal with that as well. > > > > Yes, DPS310_PRS_SHIFT_EN, DPS310_FIFO_EN, DPS310_SPI_EN are all > >wrong, but the latter 2 are not used by the driver. > > > > > >> The differences between the register map and the datasheet I'm > >>looking at make > >> me think that perhaps the driver was developed against a prototype > >>part. > >> The registers are in a different order for starters with the B0, B1 > >>and B2 > >> sets in reverse order. Any fix patch should tidy that up as well. > > > > Yes, but that's just different naming. MSB is called B2 in the > >datasheet and B0 in the driver. > > > > > >>> 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. > >> > >> Makes sense, though I can't immediately see a good solution as we > >>need > >> to maintain the remainder part. > > > > I don't have a good solution either, but there must be other IIO > >sensors that have something similar that could be possibly reused. > > > > > >>> 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. > >> Whilst the existing value seems large - I'm not great with > >>precision calcs so could > >> you lay out why 10LL is sufficient? > > > > Unless I overlooked something, the error of integer division (eg., > >discarding fractional part) is <1. In this case, the results of 7 > >integer divisions are summed, so the error is <7. When multiplying > >numerators by 10LL, the error would be <0.7. Which is OK, since we > >are interested only in the integer part. > > Unfortunately it seems that there may be more problems with the > driver. I've noticed that my device has lost sample rate and precision > settings few times. When looking at the code, it seems the settings > are not restored when dps310_reset_reinit() is called at > https://github.com/torvalds/linux/blob/8ca09d5fa3549d142c2080a72a4c70ce389163cd/drivers/iio/pressure/dps310.c#L438 > Agreed. Looks like that stuff is missing. This reset path is pretty horrible in general, so I'm not surprised a few things got missed. Should be easy enough to add a cache of those and and set them again if you want to try that. > Apparently I've also ended up with data->timeout_recovery_failed == > true at > https://github.com/torvalds/linux/blob/8ca09d5fa3549d142c2080a72a4c70ce389163cd/drivers/iio/pressure/dps310.c#L443, > but the device worked fine after just reloading the kernel module. > This is difficult to reproduce, though. Hmm. There are a few things that could cause that. Maybe something running slow, or an intermittent write failure (noisy environment or bad wire / track maybe?) > Andres
