[U-Boot] UBoot running UBoot - is it possible?

[Stefano Babic]

On 13/11/18 17:07, Simon Goldschmidt wrote:
> On 13.11.2018 17:00, Wolfgang Denk wrote:
>> Dear Simon,
>>
>> In message
>> <CAAh8qsxB3YNoDruZnmcPvkygc7HXVOcf=PNdA4xRp=PjmQANsw at mail.gmail.com>
>> you wrote:
>>> My idea was to let SPL implement a dedicated boot counter/watchdog
>>> that detects problems starting U-Boot and using a backup copy if it
>>> fails multiple times. Of course you need an SPL on your board to do
>>> this. Plus you end up with the same problem for updating SPL, but I'm
>>> lucky here that my platform (socfpga gen5) has redundant storage for
>>> SPL and implements a startup watchdog mechanism for the SPL.
>> In other words, you are just adding enough additional complexity to
>> SPL to make it reasonably likely that there will be bugs that need
>> to be fixed later, i. e. you have to update the SPL.
>>
>> And then?
>>
>> You are just moving the problem, not solving it.
> 
> That's not how I see it. As I see it, I have to implement an upgrade
> option for SPL. This is partly due to bad design of the socfpga_gen5
> platform. But also I have read multiple times on this list that you
> should use SPL from the same version as U-Boot as they might work
> combined and U-Boot might depend on SPL to do things that might change
> over time.

Right. It is not guaranteed that mixing versions works.

> So is it really a good idea to upgrade U-Boot without
> upgrading SPL at the same time?

IMHO it is a bad idea, and it forgets that the bootloader is really SPL
+ u-boot.img else just u-boot.img. It is also questionable if it makes
sense to provide an update mechanism for u-boot when most of critical
parts like clocks, DDR initialisation, etc. are in SPL.

> It seems to me this would require
> thorough testing of different version mixes...
> 

Agree, and this becomes a mess.

> So given that SPL must be upgradable, how is it more complex to detect
> U-Boot failure from SPL than from U-Boot itself?

I do not get the question - if SPL fails, it can be at any time before
you get the control. There sould be a mechanism to switch to a previous
copy of SPL, generally this is not available in hw.

Best regards,
Stefano

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