Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751461AbdFHMgH (ORCPT ); Thu, 8 Jun 2017 08:36:07 -0400 Received: from mail-wm0-f54.google.com ([74.125.82.54]:38315 "EHLO mail-wm0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751410AbdFHMgF (ORCPT ); Thu, 8 Jun 2017 08:36:05 -0400 Subject: Re: [PATCH v2 3/3] pwm: meson: improve pwm calculation precision. To: Jerome Brunet , Thierry Reding , Kevin Hilman References: <20170608122416.1993-1-jbrunet@baylibre.com> <20170608122416.1993-4-jbrunet@baylibre.com> Cc: Carlo Caione , linux-pwm@vger.kernel.org, linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org From: Neil Armstrong Organization: Baylibre Message-ID: <935f2e9a-9872-d1c5-8300-2d0697593e75@baylibre.com> Date: Thu, 8 Jun 2017 14:35:59 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170608122416.1993-4-jbrunet@baylibre.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2506 Lines: 67 On 06/08/2017 02:24 PM, Jerome Brunet wrote: > When using input clocks with high rates, such as clk81 (166MHz), the > fin_ns = NSEC_PER_SEC / fin_freq can introduce a significant error. > > Ex: fin_freq = 166666667, NSEC_PER_SEC = 1000000000 > fin_ns = 5,9999999 > > which is, of course, rounded down to 5. This introduce an error of ~20% > on the period requested from the pwm. > > This patch use ps instead of ns (and 64bits integer) to perform the > calculation. This should give a good enough precision. > > Fixes: 211ed630753d ("pwm: Add support for Meson PWM Controller") > Signed-off-by: Jerome Brunet > --- > drivers/pwm/pwm-meson.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/drivers/pwm/pwm-meson.c b/drivers/pwm/pwm-meson.c > index b911a944744a..4cdc66f7f718 100644 > --- a/drivers/pwm/pwm-meson.c > +++ b/drivers/pwm/pwm-meson.c > @@ -163,7 +163,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, > unsigned int duty, unsigned int period) > { > unsigned int pre_div, cnt, duty_cnt; > - unsigned long fin_freq = -1, fin_ns; > + unsigned long fin_freq = -1; > + u64 fin_ps; > > if (~(meson->inverter_mask >> id) & 0x1) > duty = period - duty; > @@ -179,13 +180,14 @@ static int meson_pwm_calc(struct meson_pwm *meson, > } > > dev_dbg(meson->chip.dev, "fin_freq: %lu Hz\n", fin_freq); > - fin_ns = NSEC_PER_SEC / fin_freq; > + fin_ps = ((u64)NSEC_PER_SEC * 1000) / fin_freq; > > /* Calc pre_div with the period */ > for (pre_div = 0; pre_div < MISC_CLK_DIV_MASK; pre_div++) { > - cnt = DIV_ROUND_CLOSEST(period, fin_ns * (pre_div + 1)); > - dev_dbg(meson->chip.dev, "fin_ns=%lu pre_div=%u cnt=%u\n", > - fin_ns, pre_div, cnt); > + cnt = DIV_ROUND_CLOSEST_ULL((u64)period * 1000, > + fin_ps * (pre_div + 1)); > + dev_dbg(meson->chip.dev, "fin_ps=%llu pre_div=%u cnt=%u\n", > + fin_ps, pre_div, cnt); > if (cnt <= 0xffff) > break; > } > @@ -208,7 +210,8 @@ static int meson_pwm_calc(struct meson_pwm *meson, > channel->lo = cnt; > } else { > /* Then check is we can have the duty with the same pre_div */ > - duty_cnt = DIV_ROUND_CLOSEST(duty, fin_ns * (pre_div + 1)); > + duty_cnt = DIV_ROUND_CLOSEST_ULL((u64)duty * 1000, > + fin_ps * (pre_div + 1)); > if (duty_cnt > 0xffff) { > dev_err(meson->chip.dev, "unable to get duty cycle\n"); > return -EINVAL; > Great, I missed this !! Acked-by: Neil Armstrong