[MMC] Multiple cards on one host

[MMC] Multiple cards on one host

[Sascha Hauer]

Hi,

I have a board (PXA based) which has two SD slots. It uses a gpio to
switch between the slots. In times when the MMC subsystem implemented
the bus topology our customer used this fact to connect the two slots on
a single host (although it was never intended to work with SD cards, it
seemed to work). Any idea how to implement this on recent kernels? I
thought about registering two hosts in pxamci.c, but this seems quite
hacky and I suppose I'll run into locking trouble.

Sascha

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Re: [MMC] Multiple cards on one host

[Pierre Ossman]

On Wed, 3 Sep 2008 10:43:43 +0200
Sascha Hauer <s.hauer@pengutronix.de> wrote:

> Hi,
> 
> I have a board (PXA based) which has two SD slots. It uses a gpio to
> switch between the slots. In times when the MMC subsystem implemented
> the bus topology our customer used this fact to connect the two slots on
> a single host (although it was never intended to work with SD cards, it
> seemed to work). Any idea how to implement this on recent kernels? I
> thought about registering two hosts in pxamci.c, but this seems quite
> hacky and I suppose I'll run into locking trouble.
> 

To be honest, I don't think you can sanely support it. The OMAP guys
have been playing with some kind of multiplexer in front of the
controller, but it just seems like a world of hurt to me.

Perhaps you can convert to using SPI for the second slot if the
customer really needs a design with two slots?

Rgds
-- 
     -- Pierre Ossman

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

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Re: [MMC] Multiple cards on one host

[Sascha Hauer]

On Wed, Sep 03, 2008 at 04:11:02PM +0200, Pierre Ossman wrote:
> On Wed, 3 Sep 2008 10:43:43 +0200
> Sascha Hauer <s.hauer@pengutronix.de> wrote:
> 
> > Hi,
> > 
> > I have a board (PXA based) which has two SD slots. It uses a gpio to
> > switch between the slots. In times when the MMC subsystem implemented
> > the bus topology our customer used this fact to connect the two slots on
> > a single host (although it was never intended to work with SD cards, it
> > seemed to work). Any idea how to implement this on recent kernels? I
> > thought about registering two hosts in pxamci.c, but this seems quite
> > hacky and I suppose I'll run into locking trouble.
> > 
> 
> To be honest, I don't think you can sanely support it. The OMAP guys
> have been playing with some kind of multiplexer in front of the
> controller, but it just seems like a world of hurt to me.

That's what I was afraid of. Lets see what our customer says (I hope I
won't find myself in this world of hurt)

> 
> Perhaps you can convert to using SPI for the second slot if the
> customer really needs a design with two slots?

Might be an option.

Thanks for your answer.

Sascha


-- 
 Pengutronix - Linux Solutions for Science and Industry
   Handelsregister:  Amtsgericht Hildesheim, HRA 2686
     Hannoversche Str. 2, 31134 Hildesheim, Germany
   Phone: +49-5121-206917-0 |  Fax: +49-5121-206917-9