Mailbox Hardware Support

modulename: mailbox.ko

configname: CONFIG_MAILBOX

Linux Kernel Configuration
└─>Device Drivers
└─>Mailbox Hardware Support
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Mailbox is a framework to control hardware communication between
on-chip processors through queued messages and interrupt driven
signals. Say Y if your platform supports hardware mailboxes.

source code:
drivers/mailbox/mailbox.c