Messages in this thread | | | Date | Thu, 19 Oct 2023 08:53:31 +0300 | Subject | Re: [PATCH v5 2/3] iio: accel: Support Kionix/ROHM KX022A accelerometer | From | Matti Vaittinen <> |
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On 10/18/23 22:34, Jonathan Cameron wrote: > On Wed, 18 Oct 2023 01:37:12 +0530 > Jagath Jog J <jagathjog1996@gmail.com> wrote:
Hi Jagath - and thanks!
>> Hi Matti, >> >> On Mon, Oct 24, 2022 at 6:10 PM Matti Vaittinen >> <mazziesaccount@gmail.com> wrote: >>> >>> KX022A is a 3-axis accelerometer from ROHM/Kionix. The sensor features >>> include variable ODRs, I2C and SPI control, FIFO/LIFO with watermark IRQ, >>> tap/motion detection, wake-up & back-to-sleep events, four acceleration >>> ranges (2, 4, 8 and 16g), and probably some other cool features. >> >> This is a nice driver, and I found it very helpful as a reference. >> One question regarding scale please see below. >> >>> + * range is typically +-2G/4G/8G/16G, distributed over the amount of bits. >>> + * The scale table can be calculated using >>> + * (range / 2^bits) * g = (range / 2^bits) * 9.80665 m/s^2 >>> + * => KX022A uses 16 bit (HiRes mode - assume the low 8 bits are zeroed >>> + * in low-power mode(?) ) >>> + * => +/-2G => 4 / 2^16 * 9,80665 * 10^6 (to scale to micro) >>> + * => +/-2G - 598.550415 >>> + * +/-4G - 1197.10083 >>> + * +/-8G - 2394.20166 >>> + * +/-16G - 4788.40332 >>> + */ >>> +static const int kx022a_scale_table[][2] = { >>> + { 598, 550415 }, >>> + { 1197, 100830 }, >>> + { 2394, 201660 }, >>> + { 4788, 403320 }, >>> +}; >> >> Given that the integer part is non-zero, and >> IIO_VAL_INT_PLUS_MICRO is returned for read_scale, >> As raw value will never be fractional how does this >> correspond to a reading of 9.8 m/s² for the Z-axis? > > Definitely suspicious as should be in m/s^2 for an acceleration and > it should be > > 9.8*16/2^bits > > So I think these are out by a factor of 10^6 I think you are right. Looks like I misinterpreted the meaning of IIO_VAL_INT_PLUS_MICRO when I took my first tour in the IIO with this driver. The comment above the scale table does support that assumption ... 10^6 would match such a brainfart. (This is my first thought. I will take better look at this later today and see if I can come up with a fix if no-one else has sent a patch already).
I CC'd Mehdi who has also been working on this driver.
Regarding the KX022A - I am not aware of upstream users of this IC (yet). May be you're the first lucky one :) Hence, I am tempted to just fixing the driver - but it's Jonathan who will take the splatters when **** hits the fan - so it's his call to decide whether we can still fix this. _If_ there are users who have adapted to this buggy scale (users I am not aware of) then fix will break their apps. Mehdi, do you know any users of this upstream driver?
I will ping the HQ guy who has contacts to those who might be using the driver in a downstream repository and ask him to inform potential users.
It'd be very nice to get this fixed.
Sorry and thanks!
Yours, -- Matti
-- Matti Vaittinen Linux kernel developer at ROHM Semiconductors Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
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