Hi, On 06-06-18 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).
AFAIK the 2nd superspeed USB bus is never used as such. There really is only 1 USB bus on the Type-C connector, the combined USB-2 + the 1st superspeed bus, physically these are 2 separate busses but that is purely for compatibility reasons, logically there really only is 1 bus, just like a superspeed Type-A connector has both busses physically but logically represents a single bus/port.
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 guess theoretically a device could use separate role switches / muxes for the USB-2 and USB-3 busses, but that would be weird. So lets cross that bridge when we reach it.
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?
As said lets cross that bridge when we reach it.
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 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).
The graph stuff is more Heikki's specialty so I will let Heikki answer this. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
