Re: [PATCH V2 2/4] pwm: tegra: Increase precision in pwm rate calculation

From: Laxman Dewangan <ldewangan@nvidia.com>
To: Thierry Reding <thierry.reding@gmail.com>
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
Subject: Re: [PATCH V2 2/4] pwm: tegra: Increase precision in pwm rate calculation
Date: Thu, 6 Apr 2017 22:33:55 +0530	[thread overview]
Message-ID: <58E674FB.3080006@nvidia.com> (raw)
In-Reply-To: <20170406162417.GB19312@ulmo.ba.sec>

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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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