[MMC] Multiple cards on one host - Kernel

This is a discussion on [MMC] Multiple cards on one host - Kernel ; 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 ...

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Thread: [MMC] Multiple cards on one host

  1. [MMC] Multiple cards on one host

    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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  2. Re: [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?

    Rgds
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    -- Pierre Ossman

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

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  3. 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 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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