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Thu, 8 Mar 2018 00:46:47 -0500 Received: from mail-by2nam03on0097.outbound.protection.outlook.com ([104.47.42.97]:10302 "EHLO NAM03-BY2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S965963AbeCHFFJ (ORCPT ); Thu, 8 Mar 2018 00:05:09 -0500 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: Laxman Dewangan , Thierry Reding , Sasha Levin Subject: [PATCH AUTOSEL for 4.4 009/101] pwm: tegra: Increase precision in PWM rate calculation Thread-Topic: [PATCH AUTOSEL for 4.4 009/101] pwm: tegra: Increase precision in PWM rate calculation Thread-Index: AQHTtpp6Mc2Rgbtj/kGS+079TMou1w== Date: Thu, 8 Mar 2018 05:01:12 +0000 Message-ID: <20180308050023.8548-9-alexander.levin@microsoft.com> References: <20180308050023.8548-1-alexander.levin@microsoft.com> In-Reply-To: <20180308050023.8548-1-alexander.levin@microsoft.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [52.168.54.252] x-ms-publictraffictype: Email x-microsoft-exchange-diagnostics: 1;DM5PR2101MB0727;7:yeo1dyafnLdGpvEdenLLW+81kFn560KHO8guLF2+3x8quQwxeOqTwTdnylRd2D4TTOOAcmIBSNN63YA8A0/iLk7FMnNOr0g6EXb2VgpQKsILqEaj5vZ1UujFwgnp5qwkfTXZiSsf+1A/N8LPEfo+uT6JISaLyabYOA+R8pHzGPAiIGcz71Jxp56wSX5tugCNgp66kMn5VyaZKvQo00QelgwiCGCpd9FplLCOIX8Dignq9q88Y9QY3ISxPiYUVz2L;20:iPxLSygOTSnPSJqrYw5KVqsDT5bXOYMuC4LXG4gzVGhXxS5vxbtwgey2mohHGal2HZlikoVX7ezckje1GDdOO2sQcnltQQ0NtoSHu6r4jZeipkoneD5Ewyc3VVBUenFRYXNDzuzCdCNUS6EKPDCi669bQVxC2oPoZfkaaAYwGIA= x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 83df092e-3ef9-40f5-3039-08d584b22913 x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB0727; 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rate =3D (rate + (hz / 2)) / hz; This has the precision loss in lower PWM rate. Change this to have more precision as: hz =3D DIV_ROUND_CLOSEST_ULL(NSEC_PER_SEC * 100, period_ns); rate =3D DIV_ROUND_CLOSEST(rate * 100, hz) Example: 1. period_ns =3D 16672000, PWM clock rate is 200 KHz. Based on old formula hz =3D NSEC_PER_SEC / period_ns =3D 1000000000ul/16672000 =3D 59 (59.98) rate =3D (200K + 59/2)/59 =3D 3390 Based on new method: hz =3D 5998 rate =3D DIV_ROUND_CLOSE(200000*100, 5998) =3D 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 =3D 16803898, PWM clock rate is 200 KHz. Based on old formula: hz =3D 59, rate =3D 3390 Based on new formula: hz =3D 5951, rate =3D 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 --- drivers/pwm/pwm-tegra.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/pwm/pwm-tegra.c b/drivers/pwm/pwm-tegra.c index d4de0607b502..3039fb762893 100644 --- a/drivers/pwm/pwm-tegra.c +++ b/drivers/pwm/pwm-tegra.c @@ -69,6 +69,7 @@ static int tegra_pwm_config(struct pwm_chip *chip, struct= pwm_device *pwm, struct tegra_pwm_chip *pc =3D to_tegra_pwm_chip(chip); unsigned long long c; unsigned long rate, hz; + unsigned long long ns100 =3D NSEC_PER_SEC; u32 val =3D 0; int err; =20 @@ -87,9 +88,11 @@ static int tegra_pwm_config(struct pwm_chip *chip, struc= t pwm_device *pwm, * cycles at the PWM clock rate will take period_ns nanoseconds. */ rate =3D clk_get_rate(pc->clk) >> PWM_DUTY_WIDTH; - hz =3D NSEC_PER_SEC / period_ns; =20 - rate =3D (rate + (hz / 2)) / hz; + /* Consider precision in PWM_SCALE_WIDTH rate calculation */ + ns100 *=3D 100; + hz =3D DIV_ROUND_CLOSEST_ULL(ns100, period_ns); + rate =3D DIV_ROUND_CLOSEST(rate * 100, hz); =20 /* * Since the actual PWM divider is the register's frequency divider --=20 2.14.1