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    SubjectRe: [RFC] [PATCH] Device Tree on ARM platform
    On Thu, 28 May 2009, Sascha Hauer wrote:
    > > There is the advantage of easy multiplatform support. I regularly
    > > build a single kernel image which boots on all my MPC5200 boards, and
    > > on my MPC83xx boards.
    >
    > That is not necessarily an advantage of a device tree. On ARM you can
    > also build a kernel which runs on 20+ PXA platforms at the same time.
    > (And I'm sure it can be done to even support say i.MX and PXA at the
    > same time, but this is another story)

    Well, you can run it on 20+ PXA platforms which have all their own
    machine number, but you have all the little details of each platform
    hardcoded into the kernel.

    That does not help at all when your board has 5 variants just
    different in subtle details which can not be probed or enumerated by
    inspection. That's a common scenario in the embedded world.

    So you either have 5 board numbers and all the details harcoded again
    or you add some extra magic to deduce on which variant you are running
    on.

    We have seen almost everything in the weirdness range from poking in
    some hardcoded FLASH cells over weird command line parsers up to a XML
    parser which were added to work around the limitations of the machine
    number model.

    With a device tree you can avoid that crap and provide a standardized
    interface for such cases.

    I'm not saying that the device tree will make all those problems go
    away magically, but it's orders of magnitudes better than what people
    do now.

    There is no need to force switch all of ARM to the device tree, but
    adding support for it would be a good move. Nobody wants to enforce it
    and both models can live happily side by side and we'll see which
    variant turns out to be the long term favourite solution.

    Thanks,

    tglx


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