On Wed, Mar 20, 2013 at 02:36:05PM -0500, Scott Wood 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.
Hadn't seen that command before, where is it? > >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. OK, so this does sound like a real need / use for it, and if we added the granularity of CONFIG_CMD_CACHE_FLUSH or similar, it would be reasonable to turn it on to a large number of boards for a small space savings (so lets not). My next concern is that this needs build testing (and some inspection) on say ARM where we have a weak flush_cache already. But perhaps the right answer is to say it doesn't make sense to add CONFIG_CMD_CACHE on an architecture which doesn't already provide flush_cache, so drop the weak one from this patch. -- Tom
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