rpmsg: virtio: Register the rpmsg_char device

Instantiate the rpmsg_char device on virtio RPMsg bus creation.
This provides the capability, with the RPMSG_CREATE_EPT_IOCTL ioctl,
to create RPMsg char device endpoints relying on the
rpmsg_chrdev_create_eptdev API.

Notice that the created endpoints are attached to the rpmsg_ctldev
device, but not associated to a channel.
As consequence, the endpoint source and destination addresses have to
been specified and there is no channel creation and no name service
announcement to inform the remote side.

Reviewed-by: Bjorn Andersson <[e-mail]>
Reviewed-by: Mathieu Poirier <[e-mail]>
Signed-off-by: Arnaud Pouliquen <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bjorn Andersson <[e-mail]>

drivers/rpmsg/virtio_rpmsg_bus.c

···
 	wake_up_interruptible(&vrp->sendq);
 }
 
+/*
+ * Called to expose to user a /dev/rpmsg_ctrlX interface allowing to
+ * create endpoint-to-endpoint communication without associated RPMsg channel.
+ * The endpoints are rattached to the ctrldev RPMsg device.
+ */
+static struct rpmsg_device *rpmsg_virtio_add_ctrl_dev(struct virtio_device *vdev)
+{
+	struct virtproc_info *vrp = vdev->priv;
+	struct virtio_rpmsg_channel *vch;
+	struct rpmsg_device *rpdev_ctrl;
+	int err = 0;
+
+	vch = kzalloc(sizeof(*vch), GFP_KERNEL);
+	if (!vch)
+		return ERR_PTR(-ENOMEM);
+
+	/* Link the channel to the vrp */
+	vch->vrp = vrp;
+
+	/* Assign public information to the rpmsg_device */
+	rpdev_ctrl = &vch->rpdev;
+	rpdev_ctrl->ops = &virtio_rpmsg_ops;
+
+	rpdev_ctrl->dev.parent = &vrp->vdev->dev;
+	rpdev_ctrl->dev.release = virtio_rpmsg_release_device;
+	rpdev_ctrl->little_endian = virtio_is_little_endian(vrp->vdev);
+
+	err = rpmsg_chrdev_register_device(rpdev_ctrl);
+	if (err) {
+		kfree(vch);
+		return ERR_PTR(err);
+	}
+
+	return rpdev_ctrl;
+}
+
+static void rpmsg_virtio_del_ctrl_dev(struct rpmsg_device *rpdev_ctrl)
+{
+	if (!rpdev_ctrl)
+		return;
+	kfree(to_virtio_rpmsg_channel(rpdev_ctrl));
+}
+
 static int rpmsg_probe(struct virtio_device *vdev)
 {
 	vq_callback_t *vq_cbs[] = { rpmsg_recv_done, rpmsg_xmit_done };
 	static const char * const names[] = { "input", "output" };
 	struct virtqueue *vqs[2];
 	struct virtproc_info *vrp;
-	struct virtio_rpmsg_channel *vch;
-	struct rpmsg_device *rpdev_ns;
+	struct virtio_rpmsg_channel *vch = NULL;
+	struct rpmsg_device *rpdev_ns, *rpdev_ctrl;
 	void *bufs_va;
 	int err = 0, i;
 	size_t total_buf_space;
···
 
 	vdev->priv = vrp;
 
+	rpdev_ctrl = rpmsg_virtio_add_ctrl_dev(vdev);
+	if (IS_ERR(rpdev_ctrl)) {
+		err = PTR_ERR(rpdev_ctrl);
+		goto free_coherent;
+	}
+
 	/* if supported by the remote processor, enable the name service */
 	if (virtio_has_feature(vdev, VIRTIO_RPMSG_F_NS)) {
 		vch = kzalloc(sizeof(*vch), GFP_KERNEL);
 		if (!vch) {
 			err = -ENOMEM;
-			goto free_coherent;
+			goto free_ctrldev;
 		}
 
 		/* Link the channel to our vrp */
···
 
 		err = rpmsg_ns_register_device(rpdev_ns);
 		if (err)
-			goto free_coherent;
+			goto free_vch;
 	}
 
 	/*
···
 
 	return 0;
 
-free_coherent:
+free_vch:
 	kfree(vch);
+free_ctrldev:
+	rpmsg_virtio_del_ctrl_dev(rpdev_ctrl);
+free_coherent:
 	dma_free_coherent(vdev->dev.parent, total_buf_space,
 			  bufs_va, vrp->bufs_dma);
 vqs_del: