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    SubjectRe: [PATCH 1/9] dt: Handle passed/built-in DT selection in early_init_dt_scan()
    On Thu, Nov 21, 2013 at 4:53 PM, Grant Likely <> wrote:
    >> My changes don't change the current behavior much: currently
    >> early_init_dt_scan() is already called with &__dtb_start in several places.
    >> If this is broken, it's already broken.
    > Yes, but it is called on platforms that already make that assumption
    > that __dtb_start must be copied and therefore call
    > unflatten_and_copy_devicetree(). This change makes *all* platforms do
    > that. That breaks arm, arm64, c6x, microblaze, some mips platforms, and
    > powerpc!

    arm, arm64, and powerpc don't have builtin DTBs, hence no change.
    microblaze and c6x already did "early_init_devtree(&__dtb_start)" before.

    That leaves mips, which has DT handling in too many variants, which I
    didn't all verify.

    >> > memory. The dtb section can also potentially contain multiple .dtb
    >> > blobs. In the use case that you care about you are probably only
    >> Multiple dtb blobs are currently handled in platform-specific code, which
    >> passes the right dtb to early_init_dt_scan().
    > The problem is that it makes the default dt completely random because
    > the generic code still deferrences __dtb_start.

    Only if no DT was passed by the bootloader. And only if there really
    is something at __dtb_start. Before it would fail if no DTB was passed
    by the bootloader.

    >> > thinking about one, but it is entirely possible for device drivers to
    >> > have a dtb linked in which may break this if it gets linked in a
    >> > different order. The specific example I'm thinking about is I want to
    >> > have the DT selftest code load an overlay to get testcase data from a
    >> > dtb blob.
    >> >
    >> > The other concern I have here is that I don't really want this to be the
    >> > default on a lot of platforms. ARM and PowerPC for instance should only
    >> > get the default dtb from the boot wrapper. It needs to be configurable
    >> > in some way.
    >> On ARM and PowerPC, the section is empty, hence &__dbt_start ==
    >> &__dtb_end.
    > There is no guarantee that that will always be so. The patch makes some
    > poor assumtions, but they shouldn't be difficult to fix.

    OK, how to proceed?




    Geert Uytterhoeven -- There's lots of Linux beyond ia32 --

    In personal conversations with technical people, I call myself a hacker. But
    when I'm talking to journalists I just say "programmer" or something like that.
    -- Linus Torvalds

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