linux-kernel - Re: [PATCH v2 1/3] units: Add SI metric prefix definitions

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Message-ID: <dbcd926e934dc66e17cc35c4c0d2b867474379e5.camel@perches.com>
Date:   Mon, 07 Jun 2021 08:43:02 -0700
From:   Joe Perches <joe@...ches.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        wsa@...nel.org
Subject: Re: [PATCH v2 1/3] units: Add SI metric prefix definitions

On Mon, 2021-06-07 at 18:23 +0300, 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.
[]
> diff --git a/include/linux/units.h b/include/linux/units.h
[]
> @@ -4,6 +4,22 @@
>  
>  #include <linux/math.h>
>  
> +/* Metric prefixes in accordance with Système international (d'unités) */
> +#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
> +
>  #define MILLIWATT_PER_WATT	1000L
>  #define MICROWATT_PER_MILLIWATT	1000L
>  #define MICROWATT_PER_WATT	1000000L

Somewhat surprisingly to me, this seems safe.

(though I suggest using UL and ULL rather than L and LL)

The only use of any of these seems to be:

sound/pcmcia/vx/vxp_ops.c:      [VX_MICRO]      = 0x0c,         // MICRO
sound/pcmcia/vx/vxp_ops.c:              vx_outb(chip, MICRO, level);
sound/pcmcia/vx/vxp_ops.c:                      vx_outb(chip, MICRO, vx_compute_mic_level(chip->mic_level));

and these vx_outb uses are themselves macros that prepend VX_ to the 2nd arg.