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

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

Hi Scott,

On Wed, 20 Mar 2013 17:35:51 -0500, Scott Wood
<scottwood@freescale.com> wrote:

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

I did not say "subcommand", I said "programmatic" -- precisely, I don't
like the idea that a specific command or command form is needed to
avoid a situation that can be avoided automatically.

> 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?

There is no need to change any syntax.

> -Scott

Amicalement,
-- 
Albert.