From: Sascha Hauer <s.hauer@pengutronix.de>
To: Carlo Caione <carlo.caione@gmail.com>
Cc: barebox@lists.infradead.org
Subject: Re: [PATCH] shift and clocksource
Date: Tue, 21 Jun 2011 13:53:44 +0200 [thread overview]
Message-ID: <20110621115344.GV23771@pengutronix.de> (raw)
In-Reply-To: <66AE9D1D-45EA-459B-9CC1-385EFED19880@gmail.com>
On Tue, Jun 21, 2011 at 12:08:00AM +0200, Carlo Caione wrote:
> Added clocks_calc_mult_shift()
>
> Signed-off-by: Carlo Caione <carlo.caione@gmail.com>
> ---
> common/clock.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
You should also add this to include/clock.h. Otherwise the patch looks
good.
Sascha
> 1 files changed, 55 insertions(+), 0 deletions(-)
>
> diff --git a/common/clock.c b/common/clock.c
> index 15df0ab..79c06c8 100644
> --- a/common/clock.c
> +++ b/common/clock.c
> @@ -57,6 +57,61 @@ uint64_t get_time_ns(void)
> EXPORT_SYMBOL(get_time_ns);
>
> /**
> + * clocks_calc_mult_shift - calculate mult/shift factors for scaled math of clocks
> + * @mult: pointer to mult variable
> + * @shift: pointer to shift variable
> + * @from: frequency to convert from
> + * @to: frequency to convert to
> + * @maxsec: guaranteed runtime conversion range in seconds
> + *
> + * The function evaluates the shift/mult pair for the scaled math
> + * operations of clocksources and clockevents.
> + *
> + * @to and @from are frequency values in HZ. For clock sources @to is
> + * NSEC_PER_SEC == 1GHz and @from is the counter frequency. For clock
> + * event @to is the counter frequency and @from is NSEC_PER_SEC.
> + *
> + * The @maxsec conversion range argument controls the time frame in
> + * seconds which must be covered by the runtime conversion with the
> + * calculated mult and shift factors. This guarantees that no 64bit
> + * overflow happens when the input value of the conversion is
> + * multiplied with the calculated mult factor. Larger ranges may
> + * reduce the conversion accuracy by chosing smaller mult and shift
> + * factors.
> + */
> +
> +void clocks_calc_mult_shift(uint32_t *mult, uint32_t *shift, uint32_t from, uint32_t to, uint32_t maxsec)
> +{
> + uint64_t tmp;
> + uint32_t sft, sftacc = 32;
> +
> + /*
> + * Calculate the shift factor which is limiting the conversion
> + * range:
> + */
> + tmp = ((uint64_t)maxsec * from) >> 32;
> + while (tmp) {
> + tmp >>=1;
> + sftacc--;
> + }
> +
> + /*
> + * Find the conversion shift/mult pair which has the best
> + * accuracy and fits the maxsec conversion range:
> + */
> + for (sft = 32; sft > 0; sft--) {
> + tmp = (uint64_t) to << sft;
> + tmp += from / 2;
> + do_div(tmp, from);
> + if ((tmp >> sftacc) == 0)
> + break;
> + }
> + *mult = tmp;
> + *shift = sft;
> +}
> +
> +
> +/**
> * clocksource_hz2mult - calculates mult from hz and shift
> * @hz: Clocksource frequency in Hz
> * @shift_constant: Clocksource shift factor
> --
> 1.7.5.2
>
>
--
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next prev parent reply other threads:[~2011-06-21 11:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-19 16:18 Carlo Caione
2011-06-20 6:25 ` Sascha Hauer
2011-06-20 22:08 ` [PATCH] " Carlo Caione
2011-06-21 11:53 ` Sascha Hauer [this message]
2011-06-21 18:56 ` Carlo Caione
2011-06-21 22:18 ` Sascha Hauer
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