linux-kernel - Re: [PATCH 3/4] atmel-mci: support multiple mmc slots

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Date:	Thu, 25 Sep 2008 09:05:56 +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 3/4] atmel-mci: support multiple mmc slots

On Wed, 24 Sep 2008 16:35:27 +0200
Haavard Skinnemoen <haavard.skinnemoen@...el.com> wrote:

> 
> On AP7000, the clock line is shared. Do I have to run the clock at the
> minimum of the two slots' maximum rates, or does it only matter when
> the card is being accessed?
> 

I'd say always. I'd never dare overclock something that's powered, even
if we're not currently communicating with it.

Remember to deal with the case of a powered but unclocked card. This
will primarily happen during card init, but it could should up later as
well if we start implementing aggressive power management.

> > > > (This will also get a bit more painful when/if the core starts
> > > > disabling the clock when a card is idle)
> > > 
> > > The atmel-mci driver already stops the clock between requests.
> > 
> > Then I expect a patch to remove that. Fiddling with the clock is
> > dangerous and I've seen everything from hung cards to silently broken
> > writes when you disable the clock too early after a request.
> 
> Ok. I'll see if I can fix that -- I take it you want a patch for
> 2.6.27, then?
> 

.28 should be fine. It's a pretty uncommon bug.

> > > > 
> > > > Fall back to polling?
> > > 
> > > Probably, yes. Can I fall back to polling after the host has been
> > > registered?
> > > 
> > 
> > Hmm... no. Not sure how to handle this...
> 
> I'll see if I can figure out a way to do it. I'm not giving it high
> priority since it's a fairly obscure error case which shouldn't happen
> with properly implemented board code.
> 

Agreed.

-- 
     -- Pierre Ossman

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

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