[U-Boot-Users] disabling d-cache in 'bootelf' for QNX

[Stefan Roese <sr@denx.de>]

Hi Rafal,

On Wednesday 02 January 2008, Rafal Jaworowski wrote:
> Currently do_bootelf() disables data cache just before passing control to
> the entry point:
>
>         /*
>          * QNX images require the data cache is disabled.
>          * Data cache is already flushed, so just turn it off.
>          */
>         if (dcache_status ())
>                 dcache_disable ();
>
> With this piece of code present I'm seeing strange effects (corrupt data
> access, hangs) in standalone apps running from the ELF envelope.

What platform are you testing on? PPC? If yes, which one?

> A pure 
> binary made of this same ELF works without problems. Contrary to the
> comment above, there's no quarantee in do_bootelf() code flow that all data
> cache has been flushed and it seems there needs to be flush_data_cache()
> executed before the disable.

dcache_disable() should flush the dcache itself before disabling it. At least 
this is the implementation I have seen on 405 and IIRC other PPC platforms.

> 1. Does it really hold true that QNX requires d-cache disabled upon passing
> control to it?
>
> 2. If so, this is a custom QNX thing that belongs to do_bootm_qnxelf() and
> should be handled there and not at the common ELF handling level.

Hmmm. I think that calling applications and especially OS'es is more safe with 
caches disabled then with caches enabled.

> Any objections to pushing this down to do_bootm_qnxelf()? I can provide a
> patch, but cannot test it with any QNX system. Is there anyone with such
> setup that would give this a try?

It's possible that other OS'es rely on caches being disabled too. I'm not sure 
here, but VxWorks could be one of those. Does anybody know for sure?

Thanks.

Best regards,
Stefan

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