On Mon, Apr 19, 2021 at 8:06 AM Dmitry Osipenko <digetx@xxxxxxxxx> wrote: > The driver uses > (x+23000)/280 formula for the conversion of raw temperature value, which > gives 82C for x=0, thus apparently formula is wrong because x=50000 > should give us ~25C. > > I tried to search for the datasheet with the formula, but couldn't find it. There is no public datasheet. I have never seen a non-public datasheet either. As the initial submission of the driver says: "This driver is based on information from the rough input driver in drivers/input/misc/mpu3050.c and the scratch misc driver posted by Nathan Royer in 2011. Some years have passed but this is finally a fully-fledged driver for this gyroscope. It was developed and tested on the Qualcomm APQ8060 Dragonboard." Nathans submission: https://lore.kernel.org/lkml/1309486707-1658-1-git-send-email-nroyer@xxxxxxxxxxxxxx/ (you find the threads at the bottom) This submission came from inside Invensense so it is the closest authoritative source we have. > Linus, will you be able to check whether the formula used by the driver > is correct? Thanks in advance. Sadly the code is the documentation when it comes to Invensense stuff, I am CC:ing Nathans Invensense address in the vain hope he is still working there and could help, also CC to Jean-Baptiste who was there last year and maybe can help out. I don't anymore remember exactly how I found this equation, but it wasn't from any datasheet. I vaguely remember browsing through some Android userspace sensor code. What I tend to do is dig around in old mobile phone Android trees, and there you sometimes find this information in different GPL code drops. I bet I got it from browsing some of those. Here is an example (Tegra): https://android.googlesource.com/kernel/tegra/+/dba2740d025c8e7e7e3c61d84a4f964d2c1c0ac9/drivers/misc/inv_mpu Worst case what one *can* do is to calibrate the scale, like put the device in a controlled environment of some two reasonably far apart temperatures and measure, assuming it is at least linear. Some professionals use controlled environment chambers for this. But I hope there is a better way. Yours, Linus Walleij
