[U-Boot] Appended DTB Android boot image support

[Alex Deymo]

Hi Ramon,

What "header_version" is the boot image you have? The
include/android_image.h in U-Boot is a little bit old so it only defines
the v0 format. The "unused" field in v0 was renamed to "header_version"
where 0 means v0. The v1 adds a few more fields, including a DTB/DTBO for
*recovery* mode.
See
https://android.googlesource.com/platform/system/core/+/master/mkbootimg/include/bootimg/bootimg.h

Having multiple DTs and picking one or merge overlays at runtime is a
reasonable thing and there's some documentation in AOSP on how to do it in
Android: https://source.android.com/devices/architecture/dto/multiple (and
other sections around it). There are some options on where to store these
and even a supported format for placing multiple .dtbo in a single "dtbo"
partition (but appending multiple DTBs at the end of the kernel is not one
of these).

Which are the "seconday" fields you are referring to?
I'm not familiar with the Dragonboard images, but it looks like they just
extended this over the reserved space in a different way. Maybe you can
convert the header to the newer format, but that still requires work in
U-Boot to support the new format.

Regards,
Alex


Le lun. 30 avr. 2018 à 16:17, Ramon Fried <ramon.fried at gmail.com> a écrit :

> Hi all.
> I'm currently adding support for Qualcomm Dragonboards  to U-boot as a
> primary bootloader without chain-loading using LK which is currently
> already supported in mainline U-boot.
>
> Qualcomm Android images are regular android images where the DTB's are
> appended to the image. Qualcomm used the "unused" field in the image
> header to populate the size of the DTB *.
>
> I'm looking for a more standard version for supporting these kind of
> images.
> Currently, to boot these images, you must provide DTB somewhere in mem
> and provide it as argument to bootm for instance.
>
> My goal is to add support that U-boot will parse the image, see that
> the DTB is included and use that as the FDT automatically.
>
> I'm looking at the "secondary" fields which are currently not used as
> a valid option to point to the DTB and it's size.
>
> Do you know if someone is working on something similar, or do you have
> any suggestions for the right approach to this issue ?
>
> Thanks,
> Ramon
>
> * - Actually, Qualcomm appends a pack of DTBs with offset table and
> chooses the right DTB in runtime.
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