ipc: ipc_service: Rework multi-instance backend.

Only one single IPC service backend is currently present: multi_instance
backend. This backend is heavily relying on the RPMsg multi_instance
code to instanciate and manage instances and endpoints. Samples exist
for both in the samples/subsys/ipc/ directory.

With this patch we are "unpacking" the RPMsg multi_service code to make
it more modular and reusable by different backends.

In particular we are re-organizing the code into two helper libraries:
an RPMsg library and a VRING / virtqueues static allocation library. At
the same time we rewrite the multi_instance backend to make fully use of
those new libraries and remove the old multi_instance sample.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>

include/ipc/ipc_rpmsg.h

@@ -0,0 +1,128 @@
+/*
+ * Copyright (c) 2021 Carlo Caione <ccaione@baylibre.com>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_IPC_SERVICE_IPC_RPMSG_H_
+#define ZEPHYR_INCLUDE_IPC_SERVICE_IPC_RPMSG_H_
+
+#include <ipc/ipc_service.h>
+#include <openamp/open_amp.h>
+#include <metal/device.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief IPC service RPMsg API
+ * @defgroup ipc_service_rpmsg_api IPC service RPMsg API
+ * @{
+ */
+
+/** Number of endpoints. */
+#define NUM_ENDPOINTS	CONFIG_IPC_SERVICE_NUM_ENDPOINTS_PER_INSTANCE
+
+/**
+ * @typedef rpmsg_ept_bound_cb
+ * @brief Define the bound callback.
+ *
+ * This callback is defined at instance level and it is called when an endpoint
+ * of the instance is bound.
+ *
+ * @param ept Endpoint of the instance just bound.
+ */
+typedef void (*rpmsg_ept_bound_cb)(struct ipc_ept *ept);
+
+/** @brief Endpoint structure.
+ *
+ *  Used to define an endpoint to be encapsulated in an RPMsg instance.
+ */
+struct ipc_ept {
+	/** RPMsg endpoint. */
+	struct rpmsg_endpoint ep;
+
+	/** Name of the endpoint. */
+	const char *name;
+
+	/** Bound flag. */
+	volatile bool bound;
+
+	/** Callbacks. */
+	const struct ipc_service_cb *cb;
+
+	/** Private data to be passed to the endpoint callbacks. */
+	void *priv;
+};
+
+/** @brief RPMsg instance structure.
+ *
+ *  Struct representation of an RPMsg instance.
+ */
+struct ipc_rpmsg_instance {
+	/** Endpoints in the instance. */
+	struct ipc_ept endpoint[NUM_ENDPOINTS];
+
+	/** RPMsg virtIO device. */
+	struct rpmsg_virtio_device rvdev;
+
+	/** SHM pool. */
+	struct rpmsg_virtio_shm_pool shm_pool;
+
+	/** EPT (instance) bound callback. */
+	rpmsg_ept_bound_cb bound_cb;
+
+	/** EPT (instance) callback. */
+	rpmsg_ept_cb cb;
+};
+
+/** @brief Init an RPMsg instance.
+ *
+ *  Init an RPMsg instance.
+ *
+ *  @param instance Pointer to the RPMsg instance struct.
+ *  @param role Master / Remote role.
+ *  @param shm_io SHM IO region pointer.
+ *  @param vdev VirtIO device pointer.
+ *  @param shb Shared memory region pointer.
+ *  @param size Size of the shared memory region.
+ *  @param ns_bind_cb callback handler for name service announcement without
+ *		      local endpoints waiting to bind. If NULL the
+ *		      implementation falls back to the internal implementation.
+ *
+ *  @retval -EINVAL When some parameter is missing.
+ *  @retval 0 If successful.
+ *  @retval Other errno codes depending on the OpenAMP implementation.
+ */
+int ipc_rpmsg_init(struct ipc_rpmsg_instance *instance,
+		   unsigned int role,
+		   struct metal_io_region *shm_io,
+		   struct virtio_device *vdev,
+		   void *shb, size_t size,
+		   rpmsg_ns_bind_cb ns_bind_cb);
+
+/** @brief Register an endpoint.
+ *
+ *  Register an endpoint to a provided RPMsg instance.
+ *
+ *  @param instance Pointer to the RPMsg instance struct.
+ *  @param role Master / Remote role.
+ *  @param ept Endpoint to register.
+ *
+ *  @retval -EINVAL When some parameter is missing.
+ *  @retval 0 If successful.
+ *  @retval Other errno codes depending on the OpenAMP implementation.
+ */
+int ipc_rpmsg_register_ept(struct ipc_rpmsg_instance *instance, unsigned int role,
+			   struct ipc_ept *ept);
+
+/**
+ * @}
+ */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* ZEPHYR_INCLUDE_IPC_SERVICE_IPC_RPMSG_H_ */