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

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hi Scott,

On Wed, 20 Mar 2013 14:36:05 -0500, Scott Wood
<scottwood@freescale.com> wrote:

> 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.

Still, why make it a shell command? Since this user needs a flush with
"go" and "cpu release", then we should add a programmatic global cache
flush in the "go" and "cpu release" commands.

> -Scott

Amicalement,
-- 
Albert.