On Wed, Sep 08, 2010 at 10:43:07AM -0400, Alan Stern wrote: > 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. > Yes. The same set of registers are used to control both host controller and the device controller. Interrupt line is also the same. > > 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. > As the registers are common, this gaurding is necessary. > > 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(). > udev->state is directly changed to NOT_ATTACHED. The reason, I have not used this API is that it blocks till the children device is disconnected (i.e class driver's unbind is called). Is this API have an async version? > > 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(). > According to OTG 2.0 spec, B-device should observe A-device connect signal with in 155ms (min time) after A-device suspended the bus. usb_remove_hcd blocks till the B-device and root hub are completely disconnected (class drivers unbind). ehci_irq observes the PCD interrupt and B-device disconnection is carried out in hub thread context. Before hub thread observes, this device disconnection, root hub device state and HW_ACCESSIBLE flag is cleared and gadget driver is activated. Yeah. Its all looks like hacky and racy. But could not find a better method to meet HNP timings. > > > 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. > I agree. I am trying to submit the basic OTG driver (host/device role based on Id pin state) first. So I will stick to usb_add_hcd() and usb_remove_hcd(). > > -- > 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 -- Sent by a consultant of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- 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
