On Wed, 8 Sep 2010, Pavan Kondeti wrote: > I am glad that you asked this question. It is an interesting problem. I'm not familiar with your hardware. Do the same device registers get used to control both the host controller and the device controller? If that's so then it really is not possible for both of them to exist at the same time. > The reason for removing HCD upon id float is to guard against > 1. sysfs/debugfs entries exposed by USB core/ehci > 2. auto suspend (runtime suspend) and system suspend If the host controller registers can be accessed without interfering with the operation of the device controller then there's no reason to guard against these things. > I have started manipulating HW_ACCESSIBLE flag initially and faced some > problems. This was on 2.6.29 kernel. So I have decided to use usb_add_hcd and > usb_remove_hcd upon Id state change. But this is causing problems in meeting > HNP timings. When HNP is started, host is suspended by clearing HW_ACCESSIBLE > flag, disabling autosuspend, and changing it usb state to NOT_ATTACHED. You should change the state to NOT_ATTACHED first. I hope you do this by calling usb_set_device_state(). > I really want to avoid calling usb_add_hcd() and usb_remove_hcd() and use the > same set of operations for both Id state change and HNP. If there isn't enough time then you don't have much choice. However those steps you take aren't enough to prevent intrusion before you get around to calling usb_remove_hcd(). > If we unconfigure the roothub, userspace may select it or autosuspend may > happen. Even worse, the user might reconfigure it. > How can we avoid autosuspend/system suspend and intrusion from > sysfs/debugfs without calling usb_remove_hcd? The only way would be to have the HCD check whether or not the hardware is in host mode before allowing it to do anything. On the whole, unregistering the host controller seems safer if it cannot operate without interfering with the device controller. 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
