On Fri, Sep 18, 2020 at 12:39:07PM +0200, Vincent Whitchurch wrote: > On Fri, Sep 18, 2020 at 11:47:20AM +0200, Guennadi Liakhovetski wrote: > > On Fri, Sep 18, 2020 at 09:47:45AM +0200, Arnaud POULIQUEN wrote: > > > IMO, as this API is defined in the Linux documentation [5] we should respect it, to ensure > > > one generic implementation. The RPMsg sample client[4] uses this user API, so seems to me > > > a good candidate to verify this. > > > > > > That's said, shall we multiple the RPMsg implementations in Linux with several APIs, > > > With the risk to make the RPMsg clients devices dependent on these implementations? > > > That could lead to complex code or duplications... > > > > So, no, in my understanding there aren't two competing alternative APIs, you'd never have > > to choose between them. If you're writing a driver for Linux to communicate with remote > > processors or to run on VMs, you use the existing API. If you're writing a driver for > > Linux to communicate with those VMs, you use the vhost API and whatever help is available > > for RPMsg processing. > > > > However, I can in principle imagine a single driver, written to work on both sides. > > Something like the rpmsg_char.c or maybe some networking driver. Is that what you're > > referring to? I can see that as a fun exercise, but are there any real uses for that? > > I hinted at a real use case for this in the previous mail thread[0]. > I'm exploring using rpmsg-char to allow communication between two chips, > both running Linux. rpmsg-char can be used pretty much as-is for both > sides of the userspace-to-userspace communication and (the userspace > side of the) userspace-to-kernel communication between the two chips. > > > You could do the same with VirtIO, however, it has been decided to go with two > > distinct APIs: virtio for guests and vhost for the host, noone bothered to create a > > single API for both and nobody seems to miss one. Why would we want one with RPMsg? > > I think I answered this question in the previous mail thread as well[1]: > | virtio has distinct driver and device roles so the completely different > | APIs on each side are understandable. But I don't see that distinction > | in the rpmsg API which is why it seems like a good idea to me to make it > | work from both sides of the link and allow the reuse of drivers like > | rpmsg-char, instead of imposing virtio's distinction on rpmsg. I think RPMsg is lacking real established documentation... Quating from [2]: <quote> In the current protocol, at startup, the master sends notification to remote to let it know that it can receive name service announcement. </quote> Isn't that a sufficient asymnetry? Thanks Guennadi [2] https://github.com/OpenAMP/open-amp/wiki/RPMsg-Messaging-Protocol > > [0] https://www.spinics.net/lists/linux-virtualization/msg43799.html > [1] https://www.spinics.net/lists/linux-virtualization/msg43802.html
