Commit 1b7898ee276b "powerpc/boot: Use the pre-boot decompression API" breaks boot

[Heiner Kallweit]

Am 10.10.2016 um 06:41 schrieb Michael Ellerman:
> Heiner Kallweit <hkallweit1 at gmail.com> writes:
> 
>> Am 07.10.2016 um 21:26 schrieb Heiner Kallweit:
>>> Am 07.10.2016 um 07:51 schrieb Oliver O'Halloran:
>>>> Hi, Heiner
>>>>
>>>> Could you send me a copy of the kernel .config (or which defconfig)
>>>> that you're using, the name of the HW platform that you're using and
>>>> if possible the kernel image itself?
>>>>
>>>> Thanks,
>>>> Oliver
>>>>
>>> Thanks for the quick reply. Attached are .config and cuImage.
>>> HW is a TP-Link TL-WDR4900 WiFi router (P1014-based) running OpenWRT.
>>>
>> After further checking I think I found the issue. The old gunzip code
>> handled uncompressed data transparently whilst the new one bails out
>> if it doesn't find a proper gzip header.
>> And in my case the actual kernel image is uncompressed.
>> With the following patch the system boots fine again (at least for me).
> 
> Thanks for testing and tracking it down.
> 
> I wonder why the actual image is uncompressed? Or alternately why do we
> tell uboot the image is compressed when it's not?
> 
Uboot is provided with a compressed image, but what gets compressed is
not the pure kernel image but the resulting image incl. boot wrapper code,
see this part of the wrapper script:

cuboot*)
    gzip -n -f -9 "$ofile"
    ${MKIMAGE} -A ppc -O linux -T kernel -C gzip -a "$base" -e "$entry" \
            $uboot_version -d "$ofile".gz "$ofile"

And this resulting image is decompressed by uboot already during boot.
Therefore the boot wrapper code sees an uncompressed kernel image.

IMHO in case of using cuboot no CONFIG_KERNEL_<COMPR TYPE> config option
should be set and Makefile + code in arch/powerpc/boot should be able
to deal with this situation:
- don't copy and build the decompression stuff
- use an alternative version of prep_kernel() in main.c which doesn't
  attempt to decompress the kernel image

This should be a cleaner solution than probing the kernel image whether
it's compressed or not.

Rgds, Heiner