OpenAMP support on STM32MP1
Design
The slave driver shares the same code with STM32H7 with resource table feature support. This is required for remoteproc to manage lifecycle of M4 firmware. On the master side, the Linux application opens rpmsg-tty devices to communicate with slave firmware. The default rpmsg-tty driver requires that registered endpoint must be hard-coded name rpmsg-tty. Once registered, a /dev/ttyRPMSGn device is created with n starting from 0. This implies that the /dev/ttyRPMSG0 device is the management session that runs heartbeat messages periodically and is always present as long as the M4 firmware is running. When master program starts up, it should attempt to connect to the /dev/ttyRPMSG0 channel and clear up zombie sessions on M4 firmware by sending delete session command. If succeeded, all /dev/ttyRPMSGn (starting from 1) devices would be deleted on Linux.