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

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Message-ID: <20080903161102.004f6f9e@mjolnir.drzeus.cx>
Date:	Wed, 3 Sep 2008 16:11:02 +0200
From:	Pierre Ossman <drzeus-mmc@...eus.cx>
To:	Sascha Hauer <s.hauer@...gutronix.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [MMC] Multiple cards on one host

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.

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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