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Message-ID: <dbcd926e934dc66e17cc35c4c0d2b867474379e5.camel@perches.com>
Subject: Re: [PATCH v2 1/3] units: Add SI metric prefix definitions
From:   Joe Perches <joe@perches.com>
To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Jarkko Nikula <jarkko.nikula@linux.intel.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        wsa@kernel.org
Date:   Mon, 07 Jun 2021 08:43:02 -0700
In-Reply-To: <20210607152344.57458-1-andriy.shevchenko@linux.intel.com>
References: <20210607152344.57458-1-andriy.shevchenko@linux.intel.com>
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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 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
> +
> ?#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.