On Tue, 21 Feb 2012, Pavan Kondeti wrote: > Summary of the problem: > > OTG driver monitors VBUS and ID lines. When VBUS is valid & ID is float, > it activates gadget by calling usb_gadget_vbus_connect() API. When Id is > grounded, OTG should activate HCD. But there is no standard USB core API > for this. Some MSM SoC has ci13xxx USB controller in which host and > device share the same register address space. To make > sure that HCD never access (via sysfs/debugfs & runtime PM/system PM) > hardware when peripheral mode is active, we unload HCD (usb_remove_hcd). > When Id is groundedm HCD is loaded by calling usb_add_hcd(). This works > great for Micro-A/B cable connect and disconnect. But we can not meet > HNP (Host Negotiation Protocol i.e switching to host mode from > peripheral mode) timings. > > As per my knowledge, dwc has separate address space for host and gadget. > So we might not need to completely load/unload HCD. But we should have > an API in USB core or struct hc_driver to notify host that it is no > longer active. But if we don't unload HCD completely, khubd exists for > root hub and will be running for every system resume cycle. I am not > sure of side-effects of it. We ought to be able to inactivate the HCD by setting the root hub to configuration 0 and then suspending it with wakeup disabled. That will take khubd out of the picture. The HCD would have to avoid enabling any interrupt sources in this situation. Also, a little work would be needed to avoid resuming the root hub during every system resume cycle, but it wouldn't be too hard. However, even then I don't know if we would be enable to meet the required HNP timings. 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
