On 06.06.2018 23:36, Mats Karrman wrote: > Hello Gentlemen, > > I'm trying to get my head around USB role switches in connection with Type-C > ports > and device-trees. So far I have not found much documentation, e.g. there are > no > device-tree bindings documented and really no good examples in existing device > trees, although there has been some attempts, e.g. [1] and [2]. Anyway, so I > send > you a couple of questions instead: > > 1) tcpm uses the port device struct to find a single usb_role_switch but > there is > room for three USB busses in the Type-C connector; one high speed and two (?) > super- > speed. These would not all come from the same controller (there might even be > separate controllers for host and device mode for each bus). > The case I am working on now only have a single USB2 otg controller so it > should > be possible to make that driver register a role switch but for other cases? > I imagine it would be possible to create a composite driver as a proxy for > all role > switches but that would probably be different for every platform/product - not > very elegant. Could the role switch infrastructure be extended to handle > arbitrary > sets of coordinated switches? > > 2) How should the connection between the Type-C port and the switches best be > expressed in a device tree? Using graph I presume, but should it be mixed > into the > existing "usb-connector" or should this be a separate block? > I think it is unfortunate that the graph use numeric addresses that need to be > fixed by documentation
I also do not like port numbers, I even have argued for using names during multiple discussions, but the discussion ended as is :( > and already I see problems with the current assignment > (0=HS, 1=SS, 2=SBU), e.g. if the host and device mode are handled by different > controllers. Graph do support multiple endpoints for one port but then we have > another level of magic numbers which does not exactly make things easier > (e.g. 0=dual or host controller, 1=device controller, 2=mode switch). Where do you want to use these magic numbers? To describe endpoints? I guess there should be controllable mux/switch behind the port, it could be standalone, or a part of bigger IP. Anyway it should be described by device node, probably parent of USB-C device-node, in such case only links from USB connector going to different IPs should be described using OF graphs. And in such case drivers of these devices should ask/determine/change/communicate their role using in-kernel frameworks (for example extcon). There are many different configurations of USB-C ports InterfaceControllers, Muxes/Switches, USB related devices, Alternate Mode devices, PMICs, USB-PDs, .... Could you describe particular one you have problem with, to make the discussion more specific. Regards Andrzej > > What are your thoughts on this? Please tell me I missed something and that > there is > a simple solution :-) > > BR // Mats > > [1] https://www.spinics.net/lists/linux-usb/msg168071.html > [2] https://www.spinics.net/lists/linux-usb/msg168072.html > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
