lkml.org 
[lkml]   [2013]   [Nov]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [PATCH 1/9] dt: Handle passed/built-in DT selection in early_init_dt_scan()
    From
    On Thu, Nov 21, 2013 at 4:53 PM, Grant Likely <grant.likely@secretlab.ca> 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?

    Thanks!

    Gr{oetje,eeting}s,

    Geert

    --
    Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

    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


    \
     
     \ /
      Last update: 2013-11-21 19:01    [W:7.055 / U:0.044 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site