[PATCH] firmware: scmi: Drop mmu_set_region_dcache_behaviour() misuse

[Bryan Brattlof]

On October 29, 2025 thus sayeth Anshul Dalal:
> On Tue Oct 28, 2025 at 8:46 PM IST, Marek Vasut wrote:
> > On 10/28/25 3:37 PM, Marek Vasut wrote:
> >> On 10/28/25 9:25 AM, Peng Fan wrote:
> >> 
> >> Hello Peng,
> >> 
> >>>> Subject: [PATCH] firmware: scmi: Drop
> >>>> mmu_set_region_dcache_behaviour() misuse
> >>>>
> >>>> MMU region cache behavior configuration for SCMI/SMT mailboxes is
> >>>> platform specific. Even on ARM systems, the mailbox memory may not
> >>>> even be located in any cacheable MMU region and may instead reside
> >>>> in some SRAM. Remove this non-generic cache behavior configuration
> >>>> code from generic code path.
> >>>>
> >>>> It is unlikely that any platform is affected by this change if it did
> >>>> configure its MMU regions correctly on start up. Platforms which might
> >>>> be affected are i.MX94/95 and STM32MP.
> >>>>
> >>>
> >>> If the memory is mapped before running SCMI stuff, it is ok.
> >>> But if memory is dynamic mapped at run time, there might be issue.
> >> 
> >> I wonder ... should ARM/ARM64 define CONFIG_HAVE_ARCH_IOREMAP and 
> >> implement actual ioremap() function which changes these cacheable 
> >> properties accordingly ?
> >> 
> >>> I saw TI platforms has some changes to use dynamic mappings,
> >>> I have not read the details, TBH.
> >> 
> >> Can we put the TI people on CC here ?
> >
> > +CC Anshul
> 
> This change shouldn't affect any current TI platforms since we don't
> make use of SCMI on K3 devices.
> 
> I'll CC folks working on upcoming devices in case they have any
> thoughts.
> 
> +CC Dhruva, Bryan, Kamlesh

It's my expectation is the shared buffer would always be in some 
internal SRAM which shouldn't need to be mapped. Not only does it keep 
the buffer secure on platforms that care about that but it also speeds 
up the access latencies between the different binaries.

IMHO it makes sense to rip this out and let the few architectures that 
need to do some MMU maintenance do it themselves.

~Bryan