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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 27F8FC433F5 for ; Thu, 18 Nov 2021 10:11:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0C9BF61BFB for ; Thu, 18 Nov 2021 10:11:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245631AbhKRKOk (ORCPT ); Thu, 18 Nov 2021 05:14:40 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41134 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244516AbhKRKMv (ORCPT ); Thu, 18 Nov 2021 05:12:51 -0500 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F09A7C061764; Thu, 18 Nov 2021 02:09:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To: Content-Transfer-Encoding:Content-Type:MIME-Version:References:Message-ID: Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=LbHt7EJoFhOZV5kub5JngiZnvgmRApjPOTDxo+lLz4I=; b=yn/MviBBs9GuGJOPYQtbWTc10J 3bJXszwjy2n4ksLEz5pN3TssG6jLuQ7sloPDL/FkW1EEnTXGE0uNZwSGfd1+rV/gpp31so/+LrdmE G40SSHuM6NCyJ+LOZ+jISQ3AUBIGszfgs3k7GiftgJ0f6Itusd7TgmweSscUc3rCo/98OA6l5qLLD yLuHTZsYByFB9FyvFktEV6wbXp/4+1xsCHd9UnTULsnxpE3pXDBjSE5ppcnTZxK1yfaCB+hD+dp6H rzwlQe4d3vypAQ6v76WYLKoL8tral5qXuNoHfPx7t5MyHRG/xj1DRgGWYaFjhQXoBIIhpZbWMptjt 3tp3Z5rg==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:55710) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1mneMT-0002nO-5y; Thu, 18 Nov 2021 10:09:45 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1mneMP-0003qm-4t; Thu, 18 Nov 2021 10:09:41 +0000 Date: Thu, 18 Nov 2021 10:09:41 +0000 From: "Russell King (Oracle)" To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: cgel.zte@gmail.com, linux-pwm@vger.kernel.org, alexandre.belloni@bootlin.com, Zeal Robot , linux-kernel@vger.kernel.org, ludovic.desroches@microchip.com, thierry.reding@gmail.com, Changcheng Deng , lee.jones@linaro.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] pwm: Use div64_ul instead of do_div Message-ID: References: <20211117020426.159242-1-deng.changcheng@zte.com.cn> <20211117112400.bkscb2pyavonpfsn@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20211117112400.bkscb2pyavonpfsn@pengutronix.de> Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 17, 2021 at 12:24:00PM +0100, Uwe Kleine-König wrote: > Hello, > > On Wed, Nov 17, 2021 at 02:04:26AM +0000, cgel.zte@gmail.com wrote: > > From: Changcheng Deng > > > > do_div() does a 64-by-32 division. If the divisor is unsigned long, using > > div64_ul can avoid truncation to 32-bit. > > After some research I understood your commit log. I'd write: > > do_div() does a 64-by-32 division. Here the divsor is an > unsigned long which on some platforms is 64 bit wide. So use > div64_ul instead of do_div to avoid a possible truncation. > > The priority of this patch seems to be low, as the device seems to exist > only on (32bit) arm. ... where unsigned long is 32-bit. In any case, for this to overflow, we would need to have a clock in excess of 2^32-1 Hz, or around 4GHz - and if we had such a situation on 32-bit devices, we need to change the type for holding the frequency in the clk API, and probably a lot of code in the CCF as well. Unless there is a real reason for this change, I would suggest leaving the code as is - there is absolutely no point in making these divisions more expensive unless there is a real reason. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!