[U-Boot] [RFC] command/cache: Add flush_cache command

[Wolfgang Denk]

Dear Tom,

In message <20130321122923.GB26945 at bill-the-cat> you wrote:
> 
> > Not really. Only a tiny fraction of users will ever run any standalone
> > applications, so please let's save the memory footprint for the
> > overwhelming majority of users who do not need that.
> 
> Well, can we run into this problem on ARM (v7 or v8) systems as well?

Probably.

But I wonder what the exact usage szenario is that will trigger the
problem.  If I understand correctly, this can only happen when you
perform a (manual) memory copy (either between different locations in
RAM, or from parallel NOR flash to RAM) of the code you are going to
run.

As far as I understand all other ways to load any such code (over the
network or from storage devices) already make sure to run flush_cache()
after any such load operation.


Scott: is my understanding correct that you only need this because
you are performing such memory copy ops manually?  From where / to
where are you copying, and why?


Thinking about alternatives:

- eventually we should discourage the use of "go"; it may be
  conveniend when you know what you are doing, but if it's casuing
  such problems we might be better off recommending to use 
  proper IH_TYPE_STANDALONE legacy images in combination with the
  bootm command instead.

- Also, instead of adding a new command, this could probably be
  scripted; I guess this should be roughly equivalent?

  	setenv flush_cache 'dc off;ic off;dc on;ic on'

  ??

Best regards,

Wolfgang Denk

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