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

[Scott Wood]

On 03/20/2013 05:11:57 PM, Albert ARIBAUD wrote:
> Hi Scott,
> 
> On Wed, 20 Mar 2013 14:36:05 -0500, Scott Wood
> <scottwood at 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 at 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.

Why add any new commands?  They could all be subcommands of bootm! :-)

Really, instead of adding one command, you want to modify *two*  
commands to do the same thing separately, which involves changing the  
syntax of both commands to accept memory range information?

-Scott