linux-kernel - Re: [PATCH v4 3/3] iio: imu: bmi270: add support for motion events

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Message-ID: <aHd2s987EMCdgdrJ@smile.fi.intel.com>
Date: Wed, 16 Jul 2025 12:53:55 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Gustavo Silva <gustavograzs@...il.com>
Cc: Alex Lanzano <lanzano.alex@...il.com>,
	Jonathan Cameron <jic23@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org, Lothar Rubusch <l.rubusch@...il.com>
Subject: Re: [PATCH v4 3/3] iio: imu: bmi270: add support for motion events

On Tue, Jul 15, 2025 at 08:55:35PM -0300, Gustavo Silva wrote:
> On Tue, Jul 15, 2025 at 10:49:25AM +0300, Andy Shevchenko wrote:
> > On Tue, Jul 15, 2025 at 10:37:22AM +0300, Andy Shevchenko wrote:
> > > On Fri, Jul 11, 2025 at 08:36:03PM -0300, Gustavo Silva wrote:

...

> > > > +/* 9.81 * 1000000 m/s^2 */
> > > > +#define BMI270_G_MEGA_M_S_2				9810000
> > > 
> > > I thought this is MICRO...
> > 
> > Btw, what if we use the device on poles and on equator (or even on orbital
> > station)? I'm wondering if this constant should be defined in units.h or
> > even in uAPI that user space may add a correction if needed.
> > 
> I certainly hadn't thought about these scenarios.
> FWIW, the accelerometer scale values also assume g = 9.81 m/s^2.
> For example, 0.000598 = 2 * 9.81 / 32768

Right, but this should be supplied to user space somehow. OTOH the measure error
may be high enough (what is the precision of the measurements by the way?) that
it will neglect the differences in the 'g' constant.

All the details are given in [1].

[1]: https://en.wikipedia.org/wiki/Gravity_of_Earth#:~:text=The%20precise%20strength%20of%20Earth's,/s2)%20by%20definition.

-- 
With Best Regards,
Andy Shevchenko