On Tue, Sep 10, 2024 at 08:12:07AM -0500, Doug Miller wrote: > On 9/3/2024 10:52 AM, Doug Miller wrote: > > I am trying to learn how to create an RPMSG-over-VIRTIO device > > (service) in order to perform communication between a host driver and > > a guest driver. The RPMSG-over-VIRTIO driver (client) side is fairly > > well documented and there is a good example (starting point, at least) > > in samples/rpmsg/rpmsg_client_sample.c. > > > > I see that I can create an endpoint (struct rpmsg_endpoint) using > > rpmsg_create_ept(), and from there I can use rpmsg_send() et al. and > > the rpmsg_rx_cb_t cb to perform the communications. However, this > > requires a struct rpmsg_device and it is not clear just how to get one > > that is suitable for this purpose. > > > > It appears that one or both of rpmsg_create_channel() and > > rpmsg_register_device() are needed in order to obtain a device for the > > specific host-guest communications channel. At some point, a "root" > > device is needed that will use virtio (VIRTIO_ID_RPMSG) such that new > > subdevices can be created for each host-guest pair. > > > > In addition, building a kernel with CONFIG_RPMSG, CONFIG_RPMSG_VIRTIO, > > and CONFIG_RPMSG_NS set, and doing a modprobe virtio_rpmsg_bus, seems > > to get things setup but that does not result in creation of any "root" > > rpmsg-over-virtio device. Presumably, any such device would have to be > > setup to use a specific range of addresses and also be tied to > > virtio_rpmsg_bus to ensure that virtio is used. > > > > It is also not clear if/how register_rpmsg_driver() will be required > > on the rpmsg driver side, even though the sample code does not use it. > > > > So, first questions are: > > > > * Am I looking at the correct interfaces in order to create the host > > rpmsg device side? > > * What needs to be done to get a "root" rpmsg-over-virtio device > > created (if required)? > > * How is a rpmsg-over-virtio device created for each host-guest driver > > pair, for use with rpmsg_create_ept()? > > * Does the guest side (rpmsg driver) require any special handling to > > plug-in to the host driver (rpmsg device) side? Aside from using the > > correct addresses to match device side. > > It looks to me as though the virtio_rpmsg_bus module can create a > "rpmsg_ctl" device, which could be used to create channels from which > endpoints could be created. However, when I load the virtio_rpmsg_bus, > rpmsg_ns, and rpmsg_core modules there is no "rpmsg_ctl" device created > (this is running in the host OS, before any VMs are created/run). > At this time the modules stated above are all used when a main processor is controlling a remote processor, i.e via the remoteproc subsystem. I do not know of an implementation where VIRTIO_ID_RPMSG is used in the context of a host/guest scenario. As such you will find yourself in uncharted territory. At some point there were discussion via the OpenAMP body to standardize the remoteproc's subsystem establishment of virtqueues to conform to a host/guest scenario but was abandonned. That would have been a step in the right direction for what you are trying to do. > Is this the correct way to use RPMSG-over-VIRTIO? If so, what actions > need to be taken to cause a "rpmsg_ctl" device to be created? What > method would be used (in a kernel driver) to get a pointer to the > "rpmsg_ctl" device, for use with rpmsg_create_channel()? > > > > > Thanks, > > Doug > > > > External recipient
