linux-kernel - Re: [Patch 1/1 v5] via-sdmmc: VIA MSP card reader driver support

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Date:	Tue, 28 Apr 2009 21:49:47 +0200
From:	Pierre Ossman <drzeus-mmc@...eus.cx>
To:	JosephChan@....com.tw
Cc:	linux-kernel@...r.kernel.org, arnd@...db.de, ben-linux@...ff.org
Subject: Re: [Patch 1/1 v5] via-sdmmc: VIA MSP card reader driver support

On Wed, 22 Apr 2009 01:35:29 +0800
JosephChan@....com.tw wrote:

> -----Original Message-----
> From: Pierre Ossman [mailto:drzeus-mmc@...eus.cx] 
> >> +	else if (ios->clock >=  5000000)
> >> +		clock = PCI_CLK_8M;
> >>+	else
> >>+		clock = PCI_CLK_375K;
> >>+
> 
> > This looks a bit strange. Why are you not comparing with the clock frequency you'll be setting?
> 
> Do you mean that we should check the current clock frequency before setting?

No. My point was that you compare with, for example, 5 MHz, but then
you set the clock to 8 MHz. This is very dangerous as you'll most
likely overclock things.


> 
> > You also need to set the bits stating if the controller supports the high-speed SD and/or MMC mode, otherwise the core won't go over 25/20 MHz.
> 
> 
> OK, we will add the following line in the via_init_mmc_host function:
> 
>        mmc->caps |= MMC_CAP_MMC_HIGHSPEED |MMC_CAP_SD_HIGHSPEED;
> 

You sure the controller handles MMC high-speed timings though? They are
different from SD high-speed, which is why there are two separate caps
bits.

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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