OpenAMP support on STM32H747

Requirements

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• Communication channel over RPmsg protocol
• IPM driver support for notification
• The remoteproc feature needs to be considered on slave for resource management requirement from Linux side.
• Endpoints need to be managed by session
• Established OpenAMP sessions must be acknowledged by an initial read/write pair

Implementation

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• There are problems with integrating OpenAMP APIs into CPP files, therefore helper functions are implemented in device/openamp.c.
• The communication channel use comm_buffer under the hood, which means high level protocol is stream-based. The first implementation would be OACS command set, and corresponding OpenAMPStream needs to be implemented.
• QEMU implementation on mps2_an521 helps prototyping as the remote cpu can print messages. The only difference between H747 and MPS2 is that IPM drivers are different.
• Cache needs to be configured as write-through on shared memory of H747. This is configured in device tree file.
• Simple implementation of rpmsg handshaking and default endpoint establish
  • m.clear_virtio_status
  • m.setup_virtio_region
  • m.setup_ipm
  • m.setup_vrings
  • m.rpmsg_virtio_init_shm_pool
  • m.rpmsg_init_vdev
  • m.wait_for_slave_response_from_ns_setup
  • s.setup_virtio_region
  • s.setup_ipm
  • s.setup_vrings
  • s.rpmsg_virtio_init_shm_pool
  • s.rpmsg_init_vdev
  • s.ready
  • s.register<ept=default>
  • s.ipm_notify
  • m.ipm_notified
  • m.bind<ept=default>
  • m.ready
• Typical echo flow
  • m.send(msg)
  • m.ipm_notify
  • s.ipm_notified
  • s.recv(msg)
  • s.send(msg)
  • s.ipm_notify
  • m.ipm_notified
  • m.recv(msg)
• A default session must exist as long as OpenAMP channel is established. The default session is responsible for conveying heartbeat message and managing other sessions.
• When slave boots up, the s.rpmsg_init_vdev call would block and wait for completion of m.rpmsg_init_vdev which sets virtio_status to OK (as implemented in OpenAMP Framework). The virtio_status locates at a fixed offset of the shared memory. If master is continously running, the virtio_status should remain OK, and then slave program should pass as master is already initialized. However, slave program should notify master over IPM that zombie endpoints should be freed. If master boots up in the mean time, care must be taken regarding startup timing as virtio_status would be cleared before setting to OK.
• When master boots up, the m.wait_for_slave_response_from_ns_setup needs to wait for establishing the default session. Unfortunately the slave already established default session which is a zombie one after master reboots. Therefore the master should notify slave over IPM that zombie endpoints should be freed and a new default session should be registered.
• There is no remoteproc on STM32H7. A common practice is to allow M7 and M4 to boot up individually without clock gating. This is achieved by clearing BCM4 and BCM7 in option bytes. A startup synchronization is required to avoid accessing intermittent virtio_status.