Re: Writing a driver for a card reader controller - how?

From: M. Warner Losh (imp_at_bsdimp.com)
Date: 11/26/05

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    Date: Fri, 25 Nov 2005 23:38:21 -0700 (MST)
To: listmember@thiemo.net

    In message: <20051125105626.GA99656@mygiea.ham01.thiemo.net>
                Thiemo Nordenholz <listmember@thiemo.net> writes:
    : > Do you have a copy of the MMC standard?
    : Let's say, I have access to one.

    I have access to the sanitized versions of the standard as well, but
    not the full standard.

    : > Does the MMC standard actually define a standard host interface?
    :
    : It seems to describe a set of registers, their sizes and possible content,
    : but I have yet to find out how to send the commands to the card that are
    : defined by the standard. It seems like this must be done by the controller.

    There's two sets of registers that I've been able to find. One is the
    set of hardware registers on the host which the host uses to interact
    with the card. This is the critical one to discover, because without
    it, we cannot hope to make things work with the card. Looks like
    Linux has a few different mmc bridges that they support.

    The second set is described in the sub-set of the standard I was able
    to find on the mmc web site. These registers are standard, and I
    anticipate that FreeBSD will have a mmc-bus layer that interacts with
    these things. My initial take on the newbus hierarchy will look
    something like:

                   winbondmmcbr timmcbr atmmcbr
                 | | |
              mmcbus mmcbus mmcbus
                 | | |
               mmcf mmcf mmcf

    Where each bridge driver takes care of providing a standard inteface
    to the mmcbus layer. That layer would provide the means to do
    transfers and the like. mmcf would be the interface presented to the
    user for mmc flash cards.

    There's also new mmc I/O cards that have been defined. I don't know
    if they are in use yet or not, but web searches for mmc + bluetooth
    will show some results. I'd imagine that we'd have a mmcbt driver
    that attaches to mmcbus if such devices ever become mainstream.

    mmc slots can also support sd slots (well, most sd/mmc slots are
    really sd slots, but since mmc is a subset of sd in many ways, support
    for both is often paired). sd has some potentially probelmatical
    intellectual property issues, but we should design a framework that
    would allow a sdbus, mgatebus, etc to also attach to the above
    bridges.

    Warner

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