From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <58E674FB.3080006@nvidia.com> Date: Thu, 6 Apr 2017 22:33:55 +0530 From: Laxman Dewangan MIME-Version: 1.0 Subject: Re: [PATCH V2 2/4] pwm: tegra: Increase precision in pwm rate calculation References: <1491488461-24621-1-git-send-email-ldewangan@nvidia.com> <1491488461-24621-3-git-send-email-ldewangan@nvidia.com> <20170406162417.GB19312@ulmo.ba.sec> In-Reply-To: <20170406162417.GB19312@ulmo.ba.sec> Content-Type: multipart/alternative; boundary="------------090305010106000103050904" To: Thierry Reding Cc: robh+dt@kernel.org, jonathanh@nvidia.com, mark.rutland@arm.com, linux-pwm@vger.kernel.org, devicetree@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org List-ID: --------------090305010106000103050904 Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit On Thursday 06 April 2017 09:54 PM, Thierry Reding wrote: > * PGP Signed by an unknown key > > On Thu, Apr 06, 2017 at 07:50:59PM +0530, Laxman Dewangan wrote: >> The rate of the PWM calculated as follows: >> hz = NSEC_PER_SEC / period_ns; >> rate = (rate + (hz / 2)) / hz; >> >> This has the precision loss in lower PWM rate. >> Changing this to have more precision as: >> hz = DIV_ROUND_CLOSE(NSEC_PER_SEC * 100, period_ns); >> rate = DIV_ROUND_CLOSE(rate * 100, hz) > DIV_ROUND_CLOSEST(). And I much prefer this to the actual code below. I > don't think it's necessary to have a local variable for the precision. Do you suggest to use DIV_ROUND_CLOSEST() instead of DIV_ROUND_CLOSEST_ULL()? This is ULL division and so we need to use this one. Or am I missing something --------------090305010106000103050904 Content-Type: text/html; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit
On Thursday 06 April 2017 09:54 PM, Thierry Reding wrote:
* PGP Signed by an unknown key

On Thu, Apr 06, 2017 at 07:50:59PM +0530, Laxman Dewangan wrote:

The rate of the PWM calculated as follows:
	hz = NSEC_PER_SEC / period_ns;
 	rate = (rate + (hz / 2)) / hz;

This has the precision loss in lower PWM rate.
Changing this to have more precision as:
	hz = DIV_ROUND_CLOSE(NSEC_PER_SEC * 100, period_ns);
	rate = DIV_ROUND_CLOSE(rate * 100, hz)

DIV_ROUND_CLOSEST(). And I much prefer this to the actual code below. I
don't think it's necessary to have a local variable for the precision.
Do you suggest to use DIV_ROUND_CLOSEST() instead of DIV_ROUND_CLOSEST_ULL()?

This is ULL division and so we need to use this one.

Or am I missing something
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