linux-kernel - Re: [patch 7/7] SDHCI: Add change

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Date:	Sat, 15 Nov 2008 23:57:39 +0000
From:	Ben Dooks <ben-linux@...ff.org>
To:	Pierre Ossman <drzeus-mmc@...eus.cx>
Cc:	Ben Dooks <ben-linux@...ff.org>, linux-kernel@...r.kernel.org,
	sdhci-devel@...t.drzeus.cx
Subject: Re: [patch 7/7] SDHCI: Add change_clock callback for glue drivers

On Fri, Nov 14, 2008 at 11:20:21PM +0100, Pierre Ossman wrote:
> On Mon, 03 Nov 2008 20:09:51 +0000
> Ben Dooks <ben-linux@...ff.org> wrote:
> 
> > Add a change_clock callback to allow drivers to update
> > device specific clock selections and control registers
> > when there is a change in clock.
> > 
> > Move the main part of sdhci_set_clock() to a new routine
> > which can be called by the glue drivers to do the sdhci
> > standard clock management.
> > 
> > Update the sdhci-s3c driver to use this to select the
> > appropriate clock source when clocks change.
> > 
> > Signed-off-by: Ben Dooks <ben-linux@...ff.org>
> > 
> 
> I'm afraid I don't quite follow on the requirements here. Care to
> elaborate as to why this is needed?

The controller has a number of possible clock sources, the bus clock
it is connected to (generally called hclk) and three more clocks from
the heirachy that is muxed/divided from either an 48MHz, 27MHz or the
EPLL.

The callback allows the recalculation and selection of the best clock
to run the card clock for the controller.
 
> > Index: linux.git/drivers/mmc/host/sdhci-pci.c
> > ===================================================================
> > --- linux.git.orig/drivers/mmc/host/sdhci-pci.c	2008-11-03 12:17:50.000000000 +0000
> > +++ linux.git/drivers/mmc/host/sdhci-pci.c	2008-11-03 12:18:41.000000000 +0000
> > @@ -391,6 +391,7 @@ static int sdhci_pci_enable_dma(struct s
> >  
> >  static struct sdhci_ops sdhci_pci_ops = {
> >  	.enable_dma	= sdhci_pci_enable_dma,
> > +	.change_clock	= sdhci_change_clock,
> >  };
> >  
> >  /*****************************************************************************\
> 
> This seems pointless :)
> 
> > @@ -950,6 +955,8 @@ out:
> >  	host->clock = clock;
> >  }
> >  
> > +EXPORT_SYMBOL_GPL(sdhci_set_clock);
> > +
> 
> Wrong symbol. :)

ok, will fix

-- 
Ben (ben@...ff.org, http://www.fluff.org/)

  'a smiley only costs 4 bytes'
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