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

[Stefano Babic]

Hi Simon,

On 13/11/18 18:43, Simon Goldschmidt wrote:
> 
> 
> Am Di., 13. Nov. 2018, 17:53 hat Stefano Babic <sbabic at denx.de
> <mailto:sbabic at denx.de>> geschrieben:
> 
>     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
>     <mailto: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.
> 
> 
> Unless I'm mistaken, the socfpga gen5 bootrom implements a timer and
> loads SPL from secondary storage of it does not register as successful
> after some time.

That means you *have* hardware support, then.

I am not aware there is such as feature on i.MX6.

> 
> That's my arch only, of course...

Regards,
Stefano


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