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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jcGwY-0000bb-EQ; Fri, 22 May 2020 23:19:10 +0000 Received: from alexa-out-sd-01.qualcomm.com ([199.106.114.38]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jcGwU-0000ac-UQ for linux-arm-kernel@lists.infradead.org; Fri, 22 May 2020 23:19:08 +0000 Received: from unknown (HELO ironmsg03-sd.qualcomm.com) ([10.53.140.143]) by alexa-out-sd-01.qualcomm.com with ESMTP; 22 May 2020 16:19:05 -0700 Received: from gurus-linux.qualcomm.com ([10.46.162.81]) by ironmsg03-sd.qualcomm.com with ESMTP; 22 May 2020 16:19:04 -0700 Received: by gurus-linux.qualcomm.com (Postfix, from userid 383780) id 9E1E24DEF; Fri, 22 May 2020 16:19:04 -0700 (PDT) Date: Fri, 22 May 2020 16:19:04 -0700 From: Guru Das Srinagesh To: Daniel Thompson Subject: Re: [RESEND PATCH v14 04/11] pwm: clps711x: Cast period to u32 before use as divisor Message-ID: <20200522231904.GB2873@codeaurora.org> References: <1d6918c3fc2976bdbdb687bf54a2ef09fc1558db.1589330178.git.gurus@codeaurora.org> <20200521101934.j5ivjky4e6byveut@holly.lan> <20200521202525.GA24026@codeaurora.org> <20200522093738.cko5rj4wrxfd4hxu@holly.lan> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200522093738.cko5rj4wrxfd4hxu@holly.lan> User-Agent: Mutt/1.5.21 (2010-09-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200522_161907_004222_AC7B4D2B X-CRM114-Status: GOOD ( 22.12 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org, linux-pwm@vger.kernel.org, Arnd Bergmann , David Collins , Stephen Boyd , linux-kernel@vger.kernel.org, Thierry Reding , Geert Uytterhoeven , Dan Carpenter , Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= , Joe Perches , Subbaraman Narayanamurthy , Lee Jones , Guenter Roeck Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, May 22, 2020 at 10:37:38AM +0100, Daniel Thompson wrote: > 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 ? Sorry, I don't follow the significance of 1000000000 - could you please explain? Just to clarify, what I was saying in my previous email was the following: I think it might be simpler to just throw away the short circuit and just do: s/DIV_ROUND_CLOSEST/DIV64_U64_ROUND_CLOSEST like in another patch in this series [1]. That should handle the rounding properly as per design. Is that okay? [1] https://lore.kernel.org/lkml/ca783e0f5ff7b517ce0854908f0e89b07551bfe5.1588616856.git.gurus@codeaurora.org/ Thank you. Guru Das. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel