linux-kernel - Re: [PATCH v2 4/7] atmel-mci: support multiple mmc slots

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Message-ID: <20081012175853.0d75b78f@mjolnir.drzeus.cx>
Date:	Sun, 12 Oct 2008 17:58:53 +0200
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
Cc:	kernel@...32linux.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/7] atmel-mci: support multiple mmc slots

On Sun, 12 Oct 2008 15:13:44 +0200
Haavard Skinnemoen <haavard.skinnemoen@...el.com> wrote:

> Pierre Ossman <drzeus-list@...eus.cx> wrote:
> > On Sun,  5 Oct 2008 18:21:27 +0200
> > Haavard Skinnemoen <haavard.skinnemoen@...el.com> wrote:
> > 
> > > +		/* Calculate clock divider */
> > > +		clkdiv = DIV_ROUND_UP(host->bus_hz, 2 * clock_min) - 1;
> > >  		if (clkdiv > 255) {
> > >  			dev_warn(&mmc->class_dev,
> > >  				"clock %u too slow; using %lu\n",
> > > -				ios->clock, host->bus_hz / (2 * 256));
> > > +				clock_min, host->bus_hz / (2 * 256));
> > >  			clkdiv = 255;
> > >  		}
> > >  
> > 
> > Has this ever happened, or is it just a bit defensive? :)
> > 
> > (not that there is something wrong with that)
> 
> It can happen if the controller is hooked up to a fast bus and fOD is
> slow for whatever reason. And if it does, clkdiv will wrap around and
> end up at a rate much faster than requested, so saturating it at the
> maximum divider is the safe thing to do.
> 

Isn't this calculated for f_min though so that the MMC core will never
request such a frequency?

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  rdesktop, core developer          http://www.rdesktop.org

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