On Thu, 24 Feb 2022, Stefano Stabellini wrote: > On Thu, 24 Feb 2022, Sudeep Holla wrote: > > On Tue, Feb 22, 2022 at 05:15:49PM +0000, Oleksii Moisieiev wrote: > > > Hi Sudeep, > > > > > > On Tue, Feb 22, 2022 at 04:06:37PM +0000, Sudeep Holla wrote: > > > > Hi Oleksii, > > > > > > > > My initial feedback on this. And thanks Cristian for making it so easy as > > > > you have covered most of the things in depth(which I might have not done > > > > myself that well) > > > > > > > > On Tue, Feb 22, 2022 at 11:00:03AM +0000, Cristian Marussi wrote: > > > > > On Mon, Feb 21, 2022 at 05:26:46PM +0000, Oleksii Moisieiev wrote: > > > > > > Introducing new parameter called scmi_devid to the device-tree bindings. > > > > > > This parameter should be set for the device nodes, which has > > > > > > clocks/power-domains/resets working through SCMI. > > > > > > > > I prefer you had given more details on your usage model here instead of > > > > pointing to the other Xen thread as it helps for someone without much > > > > background on Xen or your use-case to review this. > > > > > > > Let me describe the process in few words: > > > We implemented a new feature, called SCI-mediator in Xen. > > > The proposed implementation allows Guests to communicate with the Firmware using SCMI > > > protocol with SMC as a transport. Other implementation are also > > > possible, such as SCMI-Mailbox, SCPI-mailbox etc. > > > > > > In this feature Xen is the Trusted Agent, which receives the following > > > information in Xen device-tree: > > > 1) All channels should be described, each channel defined as > > > arm,scmi-shmem node; > > > 2) Scmi node arm,scmi-smc with protocols description; > > > > Sounds good so far. > > > > > 3) scmi-devid should be set in nodes, which works through SCMI. > > > > > > > Why is this needed for Guest OS, you need not populate this if Guest OS > > is not required to use it, right ? If it is needed just by Xen hypervisor, > > lets talk about that and why it is bad idea to mix that with general > > SCMI bindings. > > I'll try to help Oleksii by answering here, I hope I am not off the mark > :-) > > I think Sudeep is right, scmi-devid is not needed by the guest OS. > > The host device tree is a more interesting discussion. As the host > device tree is meant to be generic and not tied to a specific version of > Linux, it should fully describe the SCMI interface available. If the > device tree is provided to a Trusted Agent, then it should also have the > scmi-devid information, right? > > > > > On start Xen inits itself as trusted agent and requests agent > > > configuration by using BASE_DISCOVER_AGENT message. This message is sent > > > to each configured channel to get agent_id > > > > > > On Domain creation stage Xen will do the following steps: > > > 1) Assign channel to the Guest and map channel address to the Domain > > > address. For the Domain this address should be the same; > > > 2) Generate arm,scmi-shmem and arm,scmi-smc nodes if needed for Guest > > > device-tree (the device-tree which should be passed to the Guest); > > > 3) Process devices, which are passed through to this Guest and set > > > BASE_SET_DEVICE_PERMISSIONS for the scmi-devid, received from the > > > device-node; > > > > > > > I am confused here. So the Xen knows which devices are assigned to each > > Guest OS but doesn't know device ID for them, but relies on the device > > tree node ? > > Which devices go to which guest OS is a user-provided configuration. For > instance, a user can say: "assing /amba/ethernet@ff0e0000 to dom1". This > is normal and not related to SCMI: when a user configures a static > partitioning system, they decide which resources belong to which domain. > > So Xen is told that /amba/ethernet@ff0e0000 is supposed to go to dom1. > Xen proceeds to map memory and interrupts corresponding to > /amba/ethernet@ff0e0000 to dom1. So far so good. What about SCMI? > > In Oleksii's design, Xen is going to assign one of the available SCMI > channels to dom1 and restrict its permission to only > /amba/ethernet@ff0e0000. To do that, Xen needs to know the scmi-devid of > /amba/ethernet@ff0e0000. As far as I can tell there is nothing > Xen-specific in this activitity, that's why I asked Oleksii to reach out > to the upstream device tree community to improve the generic bindings > for everyone's benefits. Let's leave Linux and Xen aside for the moment. What are other possible Trusted Agents? (Maybe TF-A?) How do they get the scmi-devid? It looks like it was supposed to come from device tree but nobody got around to adding it to the binding because it is not used by Linux?
