From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-wy0-f177.google.com ([74.125.82.177]) by canuck.infradead.org with esmtps (Exim 4.76 #1 (Red Hat Linux)) id 1QYmdf-00039w-Ts for barebox@lists.infradead.org; Mon, 20 Jun 2011 22:08:17 +0000 Received: by wyf23 with SMTP id 23so3307599wyf.36 for ; Mon, 20 Jun 2011 15:08:04 -0700 (PDT) Mime-Version: 1.0 (Apple Message framework v1084) From: Carlo Caione In-Reply-To: <20110620062559.GJ23771@pengutronix.de> Date: Tue, 21 Jun 2011 00:08:00 +0200 Message-Id: <66AE9D1D-45EA-459B-9CC1-385EFED19880@gmail.com> References: <91BC1EFE-8DED-47F9-9027-DA5140A1A73E@gmail.com> <20110620062559.GJ23771@pengutronix.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: barebox-bounces@lists.infradead.org Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: [PATCH] shift and clocksource To: Sascha Hauer Cc: barebox@lists.infradead.org Added clocks_calc_mult_shift() Signed-off-by: Carlo Caione --- common/clock.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 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 _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox