From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELtlKhTxQ8zDKGgABH4N1kv3VSS3WpHf78wPO7VsYDNiBpdAR7hqMSnJf586Cy1Ll8Ro2N3y ARC-Seal: i=1; a=rsa-sha256; t=1521483886; cv=none; d=google.com; s=arc-20160816; b=bnNhmSiRmSZHh0h4EDzUSaieyvZio9lgijEtTc22Q822yrs6onKQyAfFQgZNbkg887 RfDdZO8uTHmMWqDO9CMzJK8cdrnXgsioCL1+hifVnGgx59OdzSWW5UOMX/QiL73996iZ tbyTxlP6SiaMfHAsfaPIk+s1382vVNbLdhFVM6NF0psdb1xjr9X5NeAym7tJFKmxWPLr 9TbsRGViglTdcTB21LvU0L7asSw6mbLT1q/qaZ8aBFFEuYHMCD9e8CwryLyNW90SJfM/ 8n6VzL4x6cjMckua9o8vn2Rj1ZTtb/IegeKLgdjuOKAn3a7V2CfVletU8Pk/3XfHDgMP L39g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=mime-version:user-agent:references:in-reply-to:message-id:date :subject:cc:to:from:arc-authentication-results; bh=jJcIzNGpqhTu4EcQkleIYW4XZH+7LZZMv9++QOVlE1M=; b=MfqzMahywZY03MjTQYau/YeUgUR4lRO9lKkzcUVt6E8b9BXjZCHVDvZcdcJ/DTMUJu lwLnZWxZ7QJ41IOgSPfOSknLS9B1NioSIt12eIFlqFJvfoTF9FK4ltJxPk/JlHaglTf9 EoQYb+Ht7NH06/rzUJ9HjQ4T1exHII4YseBgnOGNtRx7gRQ3SryS2ZV1O46ySGuY2Dzu RHoss9o5obc1ZmGbugLQCO/4bRG0aBVyDpfps/ldKe4TeUVpLRi3NbHM+eXi8D3zqtL9 scvWoJG1Voc/pLYZ8FIS91d6qDllsTY5CiA5h9B4c0SWBi4AQ+xo8kHWxeWMf+0xKgfm /2+g== ARC-Authentication-Results: i=1; mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org Authentication-Results: mx.google.com; spf=softfail (google.com: domain of transitioning gregkh@linuxfoundation.org does not designate 90.92.61.202 as permitted sender) smtp.mailfrom=gregkh@linuxfoundation.org From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Laxman Dewangan , Thierry Reding , Sasha Levin Subject: [PATCH 4.9 154/241] pwm: tegra: Increase precision in PWM rate calculation Date: Mon, 19 Mar 2018 19:06:59 +0100 Message-Id: <20180319180757.557584913@linuxfoundation.org> X-Mailer: git-send-email 2.16.2 In-Reply-To: <20180319180751.172155436@linuxfoundation.org> References: <20180319180751.172155436@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-LABELS: =?utf-8?b?IlxcU2VudCI=?= X-GMAIL-THRID: =?utf-8?q?1595390982053089635?= X-GMAIL-MSGID: =?utf-8?q?1595391488366735260?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Laxman Dewangan [ Upstream commit 250b76f43f57d578ebff5e7211eb2c73aa5cd6ca ] The rate of the PWM calculated as follows: hz = NSEC_PER_SEC / period_ns; rate = (rate + (hz / 2)) / hz; This has the precision loss in lower PWM rate. Change this to have more precision as: hz = DIV_ROUND_CLOSEST_ULL(NSEC_PER_SEC * 100, period_ns); rate = DIV_ROUND_CLOSEST(rate * 100, hz) Example: 1. period_ns = 16672000, PWM clock rate is 200 KHz. Based on old formula hz = NSEC_PER_SEC / period_ns = 1000000000ul/16672000 = 59 (59.98) rate = (200K + 59/2)/59 = 3390 Based on new method: hz = 5998 rate = DIV_ROUND_CLOSE(200000*100, 5998) = 3334 If we measure the PWM signal rate, we will get more accurate period with rate value of 3334 instead of 3390. 2. period_ns = 16803898, PWM clock rate is 200 KHz. Based on old formula: hz = 59, rate = 3390 Based on new formula: hz = 5951, rate = 3360 The PWM signal rate of 3360 is more near to requested period than 3333. Signed-off-by: Laxman Dewangan Signed-off-by: Thierry Reding Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/pwm/pwm-tegra.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) --- a/drivers/pwm/pwm-tegra.c +++ b/drivers/pwm/pwm-tegra.c @@ -76,6 +76,7 @@ static int tegra_pwm_config(struct pwm_c struct tegra_pwm_chip *pc = to_tegra_pwm_chip(chip); unsigned long long c = duty_ns; unsigned long rate, hz; + unsigned long long ns100 = NSEC_PER_SEC; u32 val = 0; int err; @@ -95,9 +96,11 @@ static int tegra_pwm_config(struct pwm_c * cycles at the PWM clock rate will take period_ns nanoseconds. */ rate = clk_get_rate(pc->clk) >> PWM_DUTY_WIDTH; - hz = NSEC_PER_SEC / period_ns; - rate = (rate + (hz / 2)) / hz; + /* Consider precision in PWM_SCALE_WIDTH rate calculation */ + ns100 *= 100; + hz = DIV_ROUND_CLOSEST_ULL(ns100, period_ns); + rate = DIV_ROUND_CLOSEST(rate * 100, hz); /* * Since the actual PWM divider is the register's frequency divider