Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751557AbdFHMYy (ORCPT ); Thu, 8 Jun 2017 08:24:54 -0400 Received: from mail-wm0-f48.google.com ([74.125.82.48]:36133 "EHLO mail-wm0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750914AbdFHMYk (ORCPT ); Thu, 8 Jun 2017 08:24:40 -0400 From: Jerome Brunet To: Thierry Reding , Kevin Hilman , Neil Armstrong Cc: Jerome Brunet , Carlo Caione , linux-pwm@vger.kernel.org, linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 3/3] pwm: meson: improve pwm calculation precision. Date: Thu, 8 Jun 2017 14:24:16 +0200 Message-Id: <20170608122416.1993-4-jbrunet@baylibre.com> X-Mailer: git-send-email 2.9.4 In-Reply-To: <20170608122416.1993-1-jbrunet@baylibre.com> References: <20170608122416.1993-1-jbrunet@baylibre.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2269 Lines: 63 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; -- 2.9.4