[maemo-users] dual boot with 2007 from device and 2008 from MMC - possible?

From: Frantisek Dufka dufkaf at seznam.cz
Date: Thu Nov 29 11:29:19 EET 2007
Austin Che wrote:
>     I actually had been looking at back-porting kexec into the 2.6.18
>     kernel. 

Might be worth trying too, see below

> But I just recompiled 2.6.21 with kexec on and patched
>     kexec-tools with arm patches and it does not work for me (the
>     screen just goes blank and eventually the whole device
>     reboots). kexec seems to be really quite simple (code-wise) and so
>     I can't imagine it being that difficult to figure out for someone
>     with a clue about omap.

I would expect at least two problems:

- passing right data (set of tagged structures) that comes from 
bootloader to new kernel, these are at specific physical address at boot 
time of first kernel but I think they get freed and overwritten later.

- setting hardware back to some harmless state so new kernel can 
initialize it again properly. This could be quite tricky for OMAP. Best 
for this it to kexec new kernel as early as possible before full system 
boot initializes dsp, audio, wlan, bt, camera ... Maybe even some stub 
kernel with everything uneeded stripped off could improve chances.

As for booting 2.6.18 from 2.6.21 one problem may be advanced frequency 
and voltage scaling which is not present in 2.6.18. Might be worth 
trying to force CPU clock to 333 (which will hopefully set also other 
clocks and paremeters correctly) before kexec-ing older kernel so 2.6.18 
won't be surprised too much.


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