Well, when the M4F is used as a safety processor it is typically booted from SBL/u-boot and may isolate the MCU domain from main domain/A53 to function in higher safety level. In these scenarios there is no remote proc handling of M4F life cycle management (LCM) and IPC. But, on the other hand, when the M4F is used as a non safety processor its LCM is handled by remote proc(main domain) and mailboxes for IPC are required.+required:The 'mboxes' property is marked as required but the description section above
+ - compatible
+ - reg
+ - reg-names
+ - ti,sci
+ - ti,sci-dev-id
+ - ti,sci-proc-ids
+ - resets
+ - firmware-name
+ - mboxes
clearly state the M4F can operate without IPC.