linux-kernel - Re: [RFC PATCH 0/5] Frequency resolution in CCF vs. cpufreq

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Message-ID: <20140515074724.GJ16662@pengutronix.de>
Date:	Thu, 15 May 2014 09:47:24 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>
Cc:	Mike Turquette <mturquette@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	Michal Simek <michal.simek@...inx.com>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	cpufreq@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH 0/5] Frequency resolution in CCF vs. cpufreq

On Wed, May 14, 2014 at 03:30:50PM -0700, Soren Brinkmann wrote:
> Hi,
> 
> I have one or two problems with cpufreq and the CCF, which are caused by
> rounding/different frequency resolutions.
> 
> cpufreq works with kHz, while the CCF uses Hz. On Zynq our default frequency is
> 666666666 Hz which the CCF, due to rounding, reports as 666666660. And for
Why does this happen? Isn't that a bug? What is the actual freqency?
666666666 Hz or 2000000000/3 Hz?

> cpufreq, which simply divides values it obtains through clk_round_rate() by
> 1000, 666666.
> Since passing 666666 to clk_round_rate() does not result in 666666660
> (clk_round_rate() always rounds down!), we chose to put 666667 in the OPP. This
What is OPP?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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