Messages in this thread | | | Subject | Re: [PATCH] usb: echi-hcd: Add register access check in shutdown | From | Srinivas Kandagatla <> | Date | Wed, 18 May 2016 18:06:04 +0100 |
| |
On 18/05/16 17:15, Alan Stern wrote: > 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? > Yes, this is true in ehci-msm driver, The driver does not add usb host by default in probe when phy is otg capable.
The usb host is added dynamically by the msm_otg driver depending on the the micro USB cable plug/un-plug events via extcon.
> 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? > Yes, for echi-msm driver, not sure about other host controller drivers.
> And would the same thing happen if the system started out as the host > but then used HNP to change into the peripheral? I don't think so, As the ehci->regs get populated once we enter the ehci_setup(), so ehci_halt() will never get chance to dereference null in this case.
Fault occurs only if the driver did not enter into host mode and system reboot/shutdown is requested.
--srini
> > Alan Stern >
| |