[RFC] Kbuild support for ARM FIT images

[Joel A Fernandes]

On Wed, Feb 20, 2013 at 10:26 PM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 02/20/2013 06:37 PM, Joel A Fernandes wrote:
>> Hello,
>> I've been spinning some work-in-progress patches for FIT build support
>> in the kernel.
>> With the move to multiplatform support on OMAP, I feel it is a good
>> time to add  FIT support, also looking at the proliferating number of
>> dtbs, as it is a nice way
>
> To my mind, FIT is pointless. And forcing the kernel build process to

I don't think so, there are many usecases for FIT and cleanly
embedding DTBs is a common usecase, (along with stronger checksums,
compression). That is also the basis of my ELC talk tomorrow morning
;-)
You could peruse the slides at, http://wwwelinux.org/Fit-boot to get a
better understanding of what FIT solves. With the move to
multiplatform kernels, it is quite a logical next step to add this
support to the kernel build.

> create bootloader-specific files doesn't seem like a good idea. Doing so
> would require pulling in even more outside tools into the kernel build flow.

As for pulling additional tools, dtc is already a part of the kernel
so the idea is to use existing tools.

> All you need is to copy the zImage and any relevant .dtb files into
> /boot, and have U-Boot load the relevant .dtb file by constructing the
> filename as roughly ${soc}-${board}.dtb, then use the bootz command to
> boot it. You can have a completely generic boot.scr (or built-in script).

FIT doesnt need any such bootloader variables and thus benefits from
the simplicity.

> Note: Not all (many?) U-Boot support FIT anyway, so you'd need to flash

For these boards, we can special case to doing a non-fit boot to keep
them backward-compatibility. I don't think maintaining
backward-compatibility requires any additional work, but just building
the kernel with a different make target.

Regards,
Joel