linux-kernel - Re: [MMC] Multiple cards on one host

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Message-ID: <20080903165011.GG4941@pengutronix.de>
Date:	Wed, 3 Sep 2008 18:50:11 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Pierre Ossman <drzeus-mmc@...eus.cx>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [MMC] Multiple cards on one host

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@...gutronix.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


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