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[86.9.19.6]) by smtp.gmail.com with ESMTPSA id c140sm9479234wmd.18.2020.05.22.02.37.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 22 May 2020 02:37:40 -0700 (PDT) Date: Fri, 22 May 2020 10:37:38 +0100 From: Daniel Thompson To: Guru Das Srinagesh Cc: linux-pwm@vger.kernel.org, Thierry Reding , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Subbaraman Narayanamurthy , David Collins , linux-kernel@vger.kernel.org, Joe Perches , Stephen Boyd , Lee Jones , Arnd Bergmann , Geert Uytterhoeven , Guenter Roeck , Dan Carpenter , linux-arm-kernel@lists.infradead.org Subject: Re: [RESEND PATCH v14 04/11] pwm: clps711x: Cast period to u32 before use as divisor Message-ID: <20200522093738.cko5rj4wrxfd4hxu@holly.lan> References: <1d6918c3fc2976bdbdb687bf54a2ef09fc1558db.1589330178.git.gurus@codeaurora.org> <20200521101934.j5ivjky4e6byveut@holly.lan> <20200521202525.GA24026@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200521202525.GA24026@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 21, 2020 at 01:25:25PM -0700, Guru Das Srinagesh wrote: > On Thu, May 21, 2020 at 11:19:34AM +0100, Daniel Thompson wrote: > > On Wed, May 20, 2020 at 03:55:57PM -0700, 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. > > > > > > 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..da771b1 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 (pwm->args.period > (v * 0xf)) > > > + return 0; > > > > This doesn't look right to me. > > > > DIV_ROUND_CLOSEST() does rounded division and the short circuit doesn't > > implement that. > > My initial patch [1] was to simply use DIV64_U64_ROUND_CLOSEST(), but I > got review feedback to add a short-circuit (same thread, [2]). I feel > like I should skip the short-circuiting and type casting and simply just > use DIV64_U64_ROUND_CLOSEST() - what do you think? A trivial review of pwm-clps711x.c suggests that the period is always 32-bit anyway so why not just throw away the short circuit entirely and replace with a comment saying that CLPS711X has a hard coded period that is always >1000000000 ? Daniel.