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

Scott Wood
2013-03-20T19:36:05Z

On 03/20/2013 02:15:19 PM, Tom Rini wrote:
> On Wed, Mar 20, 2013 at 11:43:15AM -0500, Scott Wood wrote:
> > On 03/20/2013 09:58:36 AM, Wolfgang Denk wrote:
> > >Dear Albert,
> > >
> > >In message <20130320145927.2031b913@lilith> you wrote:
> > >>
> > >> I do understand what it does, but I still don't get why it
> should be
> > >> done, since precisely payload control transfer happens through
> > >bootm and
> > >> the like which already properly flush cache.
> >
> > It doesn't always happen through bootm. Standalone apps use the
> > "go" command.
>
> So, to try and be a bit more verbose about this, for U-Boot
> applications
> which use 'go', we still need to ensure cache coherence, which is why
> bootm does a cache flush, we need some way to flush in this case.

It's also an issue with using the "cpu <n> release" command.

> And in this case you aren't better served by say bootelf ?

That wouldn't handle the "cpu release" case. In any case, "go" exists
and is currently the recommended way to launch a standalone application
in doc/README.standalone.

> > It's a user command! How can it be dead code? I don't know of a
> > way to include a human user in a patchset...
>
> Can you hightlight what exactly causes the world today to go off and
> fail? Is the hello_world example app sufficient in this case or do we
> need something much larger?

A user inside Freescale is running standalone performance test apps,
using both "go" and "cpu <n> release" (since the test needs to run on
all CPUs). They are seeing cache problems running on a T4240 if they
don't have this flush. This flush is architecturally required between
modifying/loading code and running it.

-Scott