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Thu, 8 Mar 2018 01:33:12 -0500 Received: from mail-bn3nam01on0102.outbound.protection.outlook.com ([104.47.33.102]:44208 "EHLO NAM01-BN3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S965544AbeCHFAB (ORCPT ); Thu, 8 Mar 2018 00:00:01 -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 4.9 015/190] pwm: tegra: Increase precision in PWM rate calculation Thread-Topic: [PATCH AUTOSEL for 4.9 015/190] pwm: tegra: Increase precision in PWM rate calculation Thread-Index: AQHTtpopMmjF9WW37kCj38IqioCeOg== Date: Thu, 8 Mar 2018 04:58:56 +0000 Message-ID: <20180308045810.8041-15-alexander.levin@microsoft.com> References: <20180308045810.8041-1-alexander.levin@microsoft.com> In-Reply-To: <20180308045810.8041-1-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;DM5PR2101MB0983;7:ghoYVSCGhpRUf6mO3meJ28Y+I66a6ZfYU0rzqQiLVBuGJ/KqblkoDrXFZzliiFx8Ks4DiwShoTPNhHnVns85M8zg7M4y1e+12Xjk6gOuoV+nJgEwDajHyFm/a9fViMPQ9K4E0e4mdWJrmm1KDAQokL3hvYXbAKuNNjCmVX/y7G44olB3o0twRiQgUtxeiV6SxX9XfaJ/EXsuRTZ22gSksIxGZCOoI2eXep4NU2yTzgQe8pOjWla4pNKccid9PRo8;20:C0PjpX8OPNXFqB153z07l629rCIiuIaGPqRHHJH1ynUTFVVV7t+VdPelr6vH+2jX2aIMzcqJPlUOnEeipZCNgTvkxK/Cym34kksuBxma12fHPZOAZ0Aw23FjqX5tKf8hmtkcErxULFOQ1XhmZgB+xHbEa0vNA0WBHjVSLq9VLtg= x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 28ccc908-1d8c-4af7-abd9-08d584b170da x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB0983; 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x-microsoft-antispam-message-info: YJSjgftqPjv0tLrBNOf1JGZB5Z4unCb/zMGVqecF3rpK2phMvC5rLuL6G5KgJQx3+xPuW9xKna2HjhC0qHwTIdHQ6oktzTo9hbFHoFaZLQyy5d9XqThucY09LsEh1/qFnfAplaaOrfGCt+J2YFo20rS39uyFvnWIq71gu0Ro3CmwoZKaXnh10wOYbFHjlWOJNjsycpQK0Fi0FPt0396A4CAAoGr1KaK0zwi9UxVRGHd+uhJq+9712Mkq3xb4fmOstqX0U/c0/6LU+LnLbTOlw0GCkhSKZE6IkvxZJnNDZYSQoRfz/qnS/U2Rx9tat4ZnTuGlxPIy6ZKkIa4KQK79BA== spamdiagnosticoutput: 1:99 spamdiagnosticmetadata: NSPM Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: microsoft.com X-MS-Exchange-CrossTenant-Network-Message-Id: 28ccc908-1d8c-4af7-abd9-08d584b170da X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Mar 2018 04:58:56.6365 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47 X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB0983 Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Laxman Dewangan [ Upstream commit 250b76f43f57d578ebff5e7211eb2c73aa5cd6ca ] The rate of the PWM calculated as follows: hz =3D NSEC_PER_SEC / period_ns; 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 e4647840cd6e..7e8906d6ab7a 100644 --- a/drivers/pwm/pwm-tegra.c +++ b/drivers/pwm/pwm-tegra.c @@ -76,6 +76,7 @@ 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 =3D duty_ns; unsigned long rate, hz; + unsigned long long ns100 =3D NSEC_PER_SEC; u32 val =3D 0; int err; =20 @@ -95,9 +96,11 @@ 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