[U-Boot] [PATCH v2 1/3] image: Make image_get_fdt work like image_get_{ram_disk, kernel}

[Simon Glass]

Hi Wolfgang,

On Sat, Nov 5, 2011 at 2:53 PM, Wolfgang Denk <wd at denx.de> wrote:
> Dear Simon Glass,
>
> In message <CAPnjgZ0bbhvZ1VPwY=0y9YZJdf+EOBgyKKVPFuAkBqy2z4L3HA at mail.gmail.com> you wrote:
>>
>> Just a quick Q. What is the ultimate intent here? Should we be aiming
>> to have U-Boot copy and decompress the data into RAM ready for Linux?
>
> Yes.
>
> Rigth from the beginning of PPCBoot / U-Boot we designed it that
> U-Boot would do all needed steps to verify, load and uncompress an
> image.  It make no sense to attach the uncompression and loading code
> to each and every image, and to download it and store it again and
> again and again.  This works really well for example on Power, only
> ARM is one of the examples where the PTB never bothered to acquaint
> themself with ideas that went beyond the capabilities of Blob or
> similar boot loaders.

OK, it makes sense to me. If U-Boot is doing some unpacking it should
do it all IMO. It is supposed to be the boot loader, not half a boot
loader. Perhaps for other boot loaders the situation is different.

>
>> In theory this should be slightly faster since U-Boot already has the
>> data in its cache. I think zImage now supports having an FDT inside
>> but what is the advantage of zImage over a uImage with compressed
>> portions?
>
> There is none.  Also, there is no advantage in attaching the DT blob
> to the Linux image/. This is only of use to braindead boot loaders.

If so can you please point me to it?

Searching for "DTB append ARM zImage" provides lots of recent
activity. The justification for this series seems to be old boot
loaders. Is there a LKML thread about why it should/shouldn't be done
in U-Boot specifically - other boot loaders may require the kernel to
do it, but for U-Boot there would need to be some sort of reason I
think.

I am currently using a hybrid solution (U-Boot loads the zImage and
DTB, then kernel decompresses zImage) and we have discussed changing
this. It may need a new build target in the kernel, but not rocket
science.

Regards,
Simon

>
> Best regards,
>
> Wolfgang Denk
>
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