On Tue, 1 Dec 2015, Alan Cooper wrote: > On Tue, Dec 1, 2015 at 2:35 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > >> I'm now sure the host in "non-compliant". > > > > It is non-compliant if it turns off Vbus power during suspend. But > > that may be caused by the platform more than by the controller itself. > > > > I wasn't able to find any document that states that VBUS must be on in > S3 mode. Hmmm, that's a little tricky. Were you able to find a document that says Vbus must be on in S0? People tend to make assumptions about these things without stating them clearly. The USB-2.0 spec says (section 7.2.1, the paragraph about root port hubs): "Systems that obtain operating power externally, either AC or DC, must supply at least five unit loads to each port." (A unit load is 100 mA.) There's no mention of suspend, S3, or anything else. However, I think we can assume this refers to the case where the root hub is not suspended. Section 7.2.3 discusses power control during suspend/resume. Among other things, it says: When a hub is in the Suspend state, it must still be able to provide the maximum current per port (one unit load of current per port for bus-powered hubs and five unit loads per port for self-powered hubs). This is necessary to support remote wakeup-capable devices that will power-up while the remainder of the system is still suspended. Although it doesn't say so explicitly, this includes root hubs as well as external hubs. The normal current draw during suspend will of course be a lot smaller than this; the maximum is needed only during the time that a downstream device is powering up because of a wakeup event. > In our SoC, the USB controller is not in the AON block so it > looses power in S3 and that disables the USB VBUS supply. If I can > prove our SoC is out of spec, I can probably get it fixed in future > chips. Maybe this reference will help. Alan Stern -- 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
