From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guru Das Srinagesh Subject: Re: [PATCH v9 04/11] pwm: clps711x: Use 64-bit division macro Date: Tue, 17 Mar 2020 16:30:05 -0700 Message-ID: <20200317233003.GA11350@codeaurora.org> References: <587f9ccae68ad7e1ce97fa8da6037292af1a5095.1584473399.git.gurus@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from alexa-out-sd-02.qualcomm.com ([199.106.114.39]:48641 "EHLO alexa-out-sd-02.qualcomm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727150AbgCQXaG (ORCPT ); Tue, 17 Mar 2020 19:30:06 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-pwm-owner@vger.kernel.org List-Id: linux-pwm@vger.kernel.org To: Arnd Bergmann Cc: Linux PWM List , Thierry Reding , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Subbaraman Narayanamurthy , "linux-kernel@vger.kernel.org" , Alexander Shiyan On Tue, Mar 17, 2020 at 11:22:06PM +0100, Arnd Bergmann wrote: > > diff --git a/drivers/pwm/pwm-clps711x.c b/drivers/pwm/pwm-clps711x.c > > index 924d39a..ba9500a 100644 > > --- a/drivers/pwm/pwm-clps711x.c > > +++ b/drivers/pwm/pwm-clps711x.c > > @@ -43,7 +43,7 @@ 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); > > + return DIV64_U64_ROUND_CLOSEST(v * 0xf, pwm->args.period); > > } > > Is it actually going to exceed U32_MAX? If not, a type cast may be > more appropriate here than the expensive 64-bit division. With the final change in this patch series, the framework will support periods that exceed U32_MAX. My concern is that using a typecast would mean that in those cases, this driver will not support > U32_MAX values. Using DIV64_U64_ROUND_CLOSEST makes the driver future proof and able to handle > U32_MAX values correctly. What do you think? Thank you. Guru Das.