linux-kernel - Re: [PATCH v4 4/5] iio: fxas21002c: add ODR/Scale support

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Message-ID: <2cd9b1674ae88f153a5afe65c151cabf308e4fe7.camel@az8.co>
Date:   Fri, 14 Sep 2018 16:26:44 +0100
From:   Afonso Bordado <afonsobordado@....co>
To:     Himanshu Jha <himanshujha199640@...il.com>
Cc:     kbuild-all@...org, jic23@...nel.org, knaack.h@....de,
        lars@...afoo.de, pmeerw@...erw.net, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v4 4/5] iio: fxas21002c: add ODR/Scale support

Hi,

Thanks for your help with this.

> And I suspect it may be originating from your code snippet:
> 
> #define FXAS21002C_SCALE(scale) (IIO_DEGREE_TO_RAD(62500U >>
> (scale)))
> 
> and looking at the implementation:
> 
> include/linux/iio/iio.h
> /**
>  * IIO_DEGREE_TO_RAD() - Convert degree to rad
>  * @deg: A value in degree
>  *
>  * Returns the given value converted from degree to rad
>  */
> #define IIO_DEGREE_TO_RAD(deg) (((deg) * 314159ULL + 9000000ULL) /
> 18000000ULL)
> 
> This '/' operator might be the culprit!
> 
> Just for checking that the error, remove the macro declaration
> `FXAS21002C_SCALE`
> plus its usage and re-cross compile using `make ARCH=i386`.
> 
> In my case I used the `div64_s64` function handles builds for both
> 32/64
> arch accordingly.

Yes, this is indeed the culprit. If `div64_s64` works the same way, I
wonder if the best option is to change the macro definition.

I can provide a patch for this along with changing the rest of the
definitions. However i would like some confirmation before starting
this.