On Thu, 21 Jan 2016, Arnd Bergmann wrote: > On Thursday 21 January 2016 17:48:32 Peter Chen wrote: > > > > > > > > So two hubs at ports 1 and 2 of the USB controller that integrates > > > the root hub and shares a device node with it. > > > > > Ok, so the "reg" is the address for certain root hub (HS or SS), not > > the unity address for the whole controller, if it is, do we really > > need to add two nodes for one physical port, HS and SS will not be used > > at the same time. And if the reg is the same, how can we know > > which node is from current recognized device. > > The "reg" is the address that the parent device uses to talk to the child > device. If you know which of the two that child is attached to, then I > think you don't need both, but I think we have to use the entire addressing. > > In Alan's example, there are six HS ports and three SS ports, but as I > understand it, there is no guarantee that the numbering between the two > is identical, and that the three SS ports always refer to the three HS > ports. In particular for devices soldered on-board (rather than connected > through a standard plug), I would guess that it is possible to connect > them to separate child devices though I have to admit that I do not > understand enough of the standard to know for sure. The spec allows for a lot of flexibility. It even allows for "tier mismatches", in which (for example) the SS connection for a particular port is routed directly to the root hub while the HS connection for the same port is routed through an intermediate hub! There is only one major constraint: With the exception of hubs, no USB device is allowed to use both the SS and the HS buses at the same time. A device has to decide on one speed and use only the corresponding bus. USB-3 hubs, on the other hand, are required to connect to both buses. They appear as two separate logical devices: a SS hub on the SS bus and a HS hub on the HS bus. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
