On Wed, 18 May 2016, Srinivas Kandagatla wrote: > On 18/05/16 15:56, Alan Stern wrote: > > On Wed, 18 May 2016, Srinivas Kandagatla wrote: > > > >> This patch adds a check in ehci_shutdown(), to make sure > >> that the register access is available before accessing registers. > >> > >> The use case is simple, for boards like DB410c where the usb host > >> or device functionality is decided based on the micro-usb cable > >> presence. If the board boots up with micro-usb connected and the > >> host driver is probed, but the ehci_setup() has not been done yet, > >> then a system shutdown would trigger below NULL pointer exception > >> without this patch. > > > > How can that happen? While the host driver is probed, the probing > > thread holds the device lock. But the system shutdown routine acquires > > the device lock before invoking the ->shutdown callback. Therefore the > > two things cannot happen concurrently. > > No, I did not mean them happening concurrently, I mean that the host > driver is up, however ehci_setup() is not done yet. I don't understand. ehci_setup() is called as part of the probe procedure. How can the host driver be up if ehci_setup() is not done yet? Are you saying that when the system is plugged into the "B" end of an OTG cable, ehci_setup() doesn't get called at all? And would the same thing happen if the system started out as the host but then used HNP to change into the peripheral? 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
