linux-kernel - Re: [PATCH 1/1] DaVinci: MMC: V4: MMC/SD controller driver for DaVinci family.

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Date:	Tue, 28 Apr 2009 21:45:31 +0200
From:	Pierre Ossman <drzeus-mmc@...eus.cx>
To:	"Kumar, Purushotam" <purushotam@...com>
Cc:	"davinci-linux-open-source@...ux.davincidsp.com" 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] DaVinci: MMC: V4: MMC/SD controller driver for
 DaVinci family.

On Fri, 17 Apr 2009 16:34:22 +0530
"Kumar, Purushotam" <purushotam@...com> wrote:

> > > +
> > > +	if (mmc_freq > mmc_req_freq)
> > > +		mmc_push_pull = mmc_push_pull + 1;
> > 
> > The naming of the divider is a bit confusing here. :)
> 
> I am thinking to change " mmc_push_pull" to " mmc_push_pull_divider". Please suggest other appropriate name.
> 

Or just "divider". The rest should be clear from the context.

> > > +	if (ios->bus_mode == MMC_BUSMODE_OPENDRAIN) {
> > > +		u32 temp;
> > > +
> > > +		/* Ignoring the init clock value passed for fixing the inter
> > > +		 * operability with different cards.
> > > +		 */
> > > +		open_drain_freq = ((unsigned int)cpu_arm_clk
> > > +				/ (2 * MMCSD_INIT_CLOCK)) - 1;
> > > +
> > > +		if (open_drain_freq > 0xFF)
> > > +			open_drain_freq = 0xFF;
> > > +
> > > +		temp = readl(host->base + DAVINCI_MMCCLK) & ~MMCCLK_CLKRT_MASK;
> > > +		temp |= open_drain_freq;
> > > +		writel(temp, host->base + DAVINCI_MMCCLK);
> > > +
> > > +		/* Convert ns to clock cycles */
> > > +		ns_in_one_cycle = (1000000) / (MMCSD_INIT_CLOCK/1000);
> > 
> > I'm still not sure why you need this. Open drain mode is always used at
> > a low frequency anyway.
> 
> 
> If my understanding is correct you are suggesting that at lower freq. there is no need to update the timeout parameter and can use the default value of ns_in_one_cycle.
> 
> The mmc_davinci_prepare_data() may  be called even during open drain frequency mode and here we are calculating the timeout value and updating the timeout reg. So ns_in_one_cycle should hold a proper value once we call mmc_davinci_prepare_data(). I think there is no harm in having this calculation here.
> 

I see. I thought this was some fiddling to override the core's decision
on clock frequency.

Why do you need to calculate the timeout differently based on
push-pull/open drain mode though?

Rgds
-- 
     -- Pierre Ossman

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

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