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Date:   Mon, 7 Jun 2021 17:24:44 +0300
From:   Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To:     Jarkko Nikula <jarkko.nikula@linux.intel.com>
Cc:     linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        wsa@kernel.org
Subject: Re: [PATCH resend v1 1/3] units: Add SI metric prefix definitions
Message-ID: <YL4sLLQ/Y+GafaeH@smile.fi.intel.com>
References: <20210603160433.35816-1-andriy.shevchenko@linux.intel.com>
 <0466dab7-f2d2-3b7c-52a6-a12a6b09a67f@linux.intel.com>
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Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
Precedence: bulk

On Mon, Jun 07, 2021 at 03:33:31PM +0300, Jarkko Nikula wrote:
> On 6/3/21 7:04 PM, Andy Shevchenko wrote:
> > Sometimes it's useful to have well-defined SI metric prefix to be used
> > to self-describe the formulas or equations.
> > 
> > List most popular ones in the units.h.

...

> > +/* Metric prefixes in accordance with Syst?me international (d'unit?s) */
> > +#define PETA	1000000000000000LL
> > +#define TERA	1000000000000LL
> > +#define GIGA	1000000000L
> > +#define MEGA	1000000L
> > +#define KILO	1000L
> > +#define HECTO	100L
> > +#define DECA	10L
> > +#define DECI	10L
> > +#define CENTI	100L
> > +#define MILLI	1000L
> > +#define MICRO	1000000L
> > +#define NANO	1000000000L
> > +#define PICO	1000000000000LL
> > +#define FEMTO	1000000000000000LL
> 
> For me milli is always 1/1000.

For me as well. Kernel does not operate with float point numbers.
That's why it's ordered like this.

> Might lead to confusion with these defines if
> idea is to multiply with KILO but divide with MILLI?

If the author of the hypothetical driver doesn't understand this, maybe
they can ask first, but I am an optimist here and I assume that whoever
writes the driver for a sensor / etc has a minimum education to see
what's needed for the certain case.

-- 
With Best Regards,
Andy Shevchenko