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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 634B1C54FCB for ; Fri, 24 Apr 2020 22:21:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 44A2920736 for ; Fri, 24 Apr 2020 22:21:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726234AbgDXWVb (ORCPT ); Fri, 24 Apr 2020 18:21:31 -0400 Received: from alexa-out-sd-01.qualcomm.com ([199.106.114.38]:55410 "EHLO alexa-out-sd-01.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725874AbgDXWVb (ORCPT ); Fri, 24 Apr 2020 18:21:31 -0400 Received: from unknown (HELO ironmsg03-sd.qualcomm.com) ([10.53.140.143]) by alexa-out-sd-01.qualcomm.com with ESMTP; 24 Apr 2020 15:21:30 -0700 Received: from gurus-linux.qualcomm.com ([10.46.162.81]) by ironmsg03-sd.qualcomm.com with ESMTP; 24 Apr 2020 15:21:29 -0700 Received: by gurus-linux.qualcomm.com (Postfix, from userid 383780) id E22914C90; Fri, 24 Apr 2020 15:21:29 -0700 (PDT) Date: Fri, 24 Apr 2020 15:21:29 -0700 From: Guru Das Srinagesh To: Geert Uytterhoeven Cc: Linux PWM List , Thierry Reding , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Subbaraman Narayanamurthy , David Collins , Linux Kernel Mailing List , Alexander Shiyan , Arnd Bergmann Subject: Re: [PATCH v13 04/11] pwm: clps711x: Cast period to u32 before use as divisor Message-ID: <20200424222129.GC31118@codeaurora.org> References: <02ba64d8289bf84a8d140f5a3c38ed64a9474d3b.1587523702.git.gurus@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Apr 23, 2020 at 11:30:19AM +0200, Geert Uytterhoeven wrote: > On Wed, Apr 22, 2020 at 5:00 AM Guru Das Srinagesh wrote: > > Since the PWM framework is switching struct pwm_args.period's datatype > > to u64, prepare for this transition by typecasting it to u32. > > > > Also, since the dividend is still a 32-bit number, any divisor greater > > than the numerator will cause the quotient to be zero, so return 0 in > > that case to efficiently skip the division. > > > > Cc: Alexander Shiyan > > Cc: Arnd Bergmann > > > > Signed-off-by: Guru Das Srinagesh > > --- > > drivers/pwm/pwm-clps711x.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > > index 924d39a..0d368ac 100644 > > --- a/drivers/pwm/pwm-clps711x.c > > +++ b/drivers/pwm/pwm-clps711x.c > > @@ -43,7 +43,10 @@ static void clps711x_pwm_update_val(struct clps711x_chip *priv, u32 n, u32 v) > > static unsigned int clps711x_get_duty(struct pwm_device *pwm, unsigned int v) > > { > > /* Duty cycle 0..15 max */ > > - return DIV_ROUND_CLOSEST(v * 0xf, pwm->args.period); > > + if ((u32)pwm->args.period > (v * 0xf)) > > Shouldn't the cast be removed from the expression above? > Else a period larger than or equal to 2^32 may be accepted, but truncated > silently. And even cause a division by zero error. I agree. Will remove the cast in the next patchset. Thank you. Guru Das.