On Thu, Nov 21, 2013 at 1:21 PM, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote:
>> bool __init early_init_dt_scan(void *params)
>> {
>> - if (!params)
>> - return false;
>> -
>> /* Setup flat device-tree pointer */
>> initial_boot_params = params;
>>
>> - /* check device tree validity */
>> - if (be32_to_cpu(initial_boot_params->magic) != OF_DT_HEADER) {
>> - initial_boot_params = NULL;
>> - return false;
>> + /* check passed device tree validity */
>> + if (initial_boot_params &&
>> + be32_to_cpu(initial_boot_params->magic) == OF_DT_HEADER) {
>> + pr_info("FDT at %p\n", initial_boot_params);
>> + goto found;
>> + }
>> +
>> + /* check built-in device tree validity */
>> + initial_boot_params = &__dtb_start;
>> + if (__dtb_end != (void *)&__dtb_start &&
>> + be32_to_cpu(initial_boot_params->magic) == OF_DT_HEADER) {
>> + pr_info("Compiled-in FDT at %p\n", initial_boot_params);
>> + goto found;
>
> __dtb_start is in an init section which is discarded after initcalls.
> For this to work, the dtb needs to be copied into a region of allocated
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.
> 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().
> 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.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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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