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SubjectRe: [MMC] Multiple cards on one host
On Wed, 3 Sep 2008 10:43:43 +0200
Sascha Hauer <> 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?

-- Pierre Ossman

Linux kernel, MMC maintainer
rdesktop, core developer

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