From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3365C10DCE for ; Thu, 12 Mar 2020 09:14:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C39ED2067C for ; Thu, 12 Mar 2020 09:14:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726569AbgCLJOO convert rfc822-to-8bit (ORCPT ); Thu, 12 Mar 2020 05:14:14 -0400 Received: from eu-smtp-delivery-151.mimecast.com ([146.101.78.151]:57091 "EHLO eu-smtp-delivery-151.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726390AbgCLJOO (ORCPT ); Thu, 12 Mar 2020 05:14:14 -0400 Received: from AcuMS.aculab.com (156.67.243.126 [156.67.243.126]) (Using TLS) by relay.mimecast.com with ESMTP id uk-mta-9-6SWbZ0TDPPuNfXXMJ3Jmdw-1; Thu, 12 Mar 2020 09:14:10 +0000 X-MC-Unique: 6SWbZ0TDPPuNfXXMJ3Jmdw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) by AcuMS.aculab.com (fd9f:af1c:a25b:0:43c:695e:880f:8750) with Microsoft SMTP Server (TLS) id 15.0.1347.2; Thu, 12 Mar 2020 09:14:09 +0000 Received: from AcuMS.Aculab.com ([fe80::43c:695e:880f:8750]) by AcuMS.aculab.com ([fe80::43c:695e:880f:8750%12]) with mapi id 15.00.1347.000; Thu, 12 Mar 2020 09:14:09 +0000 From: David Laight To: 'Guru Das Srinagesh' CC: "linux-pwm@vger.kernel.org" , Thierry Reding , =?iso-8859-1?Q?Uwe_Kleine-K=F6nig?= , Subbaraman Narayanamurthy , "linux-kernel@vger.kernel.org" , "Michael Turquette" , Stephen Boyd , "linux-clk@vger.kernel.org" Subject: RE: [PATCH v8 01/12] clk: pwm: Use 64-bit division function Thread-Topic: [PATCH v8 01/12] clk: pwm: Use 64-bit division function Thread-Index: AQHV90YvPG+mI4RpM0Wy3POJxK2r86hDnJdAgACbbwCAAHWSkA== Date: Thu, 12 Mar 2020 09:14:09 +0000 Message-ID: References: <338966686a673c241905716c90049993e7bb7d6a.1583889178.git.gurus@codeaurora.org> <7506bc2972324fd286dac6327ec73a3a@AcuMS.aculab.com> <20200312020938.GA14827@codeaurora.org> In-Reply-To: <20200312020938.GA14827@codeaurora.org> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Guru Das Srinagesh > Sent: 12 March 2020 02:10 > On Wed, Mar 11, 2020 at 04:58:24PM +0000, David Laight wrote: > > From: Guru Das Srinagesh > > > Sent: 11 March 2020 01:41 > > > > > > Since the PWM framework is switching struct pwm_args.period's datatype > > > to u64, prepare for this transition by using div64_u64 to handle a > > > 64-bit divisor. > > > ... > > > --- a/drivers/clk/clk-pwm.c > > > +++ b/drivers/clk/clk-pwm.c > > > @@ -89,7 +89,7 @@ static int clk_pwm_probe(struct platform_device *pdev) > > > } > > > > > > if (of_property_read_u32(node, "clock-frequency", &clk_pwm->fixed_rate)) > > > - clk_pwm->fixed_rate = NSEC_PER_SEC / pargs.period; > > > + clk_pwm->fixed_rate = div64_u64(NSEC_PER_SEC, pargs.period); > > > > That cannot be needed, a 32 bit division is fine. > > Could you please explain why? I think the use of this function is > warranted in order to handle the division properly with a 64-bit > divisor. ... > > I'd assign pargs.period to an 'unsigned int' variable > > prior to the division (I hate casts - been bitten by them in the past.). > > Wouldn't this truncate the 64-bit value? The intention behind this patch > is to allow the processing of 64-bit values in full. You are dividing a 32bit constant by a value. If pargs.period is greater than 2^32 the result is zero. I think you divide by 'fixed_rate' a bit later on - better not be zero. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)