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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29885C433EF for ; Thu, 10 Feb 2022 09:49:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239016AbiBJJs5 convert rfc822-to-8bit (ORCPT ); Thu, 10 Feb 2022 04:48:57 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:36390 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239025AbiBJJss (ORCPT ); Thu, 10 Feb 2022 04:48:48 -0500 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id EC204138 for ; Thu, 10 Feb 2022 01:48:48 -0800 (PST) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-48-zq-35qpQOqaQZ_cZnG8zjw-1; Thu, 10 Feb 2022 09:48:45 +0000 X-MC-Unique: zq-35qpQOqaQZ_cZnG8zjw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.28; Thu, 10 Feb 2022 09:48:44 +0000 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.028; Thu, 10 Feb 2022 09:48:44 +0000 From: David Laight To: =?iso-8859-1?Q?=27Uwe_Kleine-K=F6nig=27?= , Qing Wang CC: Thierry Reding , Lee Jones , "linux-pwm@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH] pwm: use div64_u64() instead of do_div() Thread-Topic: [PATCH] pwm: use div64_u64() instead of do_div() Thread-Index: AQHYHclpMmDYeR7Hx0KRNkbIRj4HSKyMibOg Date: Thu, 10 Feb 2022 09:48:44 +0000 Message-ID: <9273cd6497354dd882faf55b194ff590@AcuMS.aculab.com> References: <1644395998-4397-1-git-send-email-wangqing@vivo.com> <20220209152609.gqeivcehkuzgz3sk@pengutronix.de> In-Reply-To: <20220209152609.gqeivcehkuzgz3sk@pengutronix.de> Accept-Language: en-GB, 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 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Uwe Kleine-König > Sent: 09 February 2022 15:26 ... > > - do_div(cycles, period_ns); > > + div64_u64(cycles, period_ns); > > This is wrong, div64_u64() has a different calling convention than do_div(). > > The issue however is real. Please add Not really although I can't see a check I'd assume that period_ns is expected to be much less than a second - so well under 32 bits There is certainly a general expectation that multiplying by other 'largish' values won't exceed 64 bits. Plausible the pwm 'period' should actually be a u32. But then care would be needed to ensure the multiplies have 64bit results. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)