Hi, Wesley Cheng <wcheng@xxxxxxxxxxxxxx> writes: >>>> From: Hemant Kumar <hemantk@xxxxxxxxxxxxxx> >>>> >>>> Upon driver unbind usb_free_all_descriptors() function frees all >>>> speed descriptor pointers without setting them to NULL. In case >>>> gadget speed changes (i.e from super speed plus to super speed) >>>> after driver unbind only upto super speed descriptor pointers get >>>> populated. Super speed plus desc still holds the stale (already >>>> freed) pointer. Fix this issue by setting all descriptor pointers >>>> to NULL after freeing them in usb_free_all_descriptors(). >>> >>> could you describe this a little better? How can one trigger this case? >>> Is the speed demotion happening after unbinding? It's not clear how to >>> cause this bug. >>> >> Hi Felipe, >> >> Internally, we have a mechanism to switch the DWC3 core maximum speed >> parameter dynamically for displayport use cases. This issue happens >> whenever we have a maximum speed change occur on the USB gadget, which >> for DWC3 happens whenever we call gadget init. When we switch in and >> out of host mode, gadget init is being executed, leading to the change >> in the USB gadget max speed parameter: >> >> dwc->gadget->max_speed = dwc->maximum_speed; >> >> I know that configFS gadget has the max_speed sysfs file, which is a >> similar mechanism, but I haven't tried to see if we can reproduce the >> same issue with it. Let me see if we can reproduce this with that >> configfs speed setting. >> >> Thanks >> Wesley Cheng >> > > Hi Felipe, > > So I tried with doing it through the configFS max_speed, but it doesn't > have the same effect, as the setting done in dwc3_gadget_init() will > still be assigning the composite/UDC device's maximum speed to SSP/SS. > This is what the usb_assign_descriptor() uses to determine whether or > not to copy the SSP and SS descriptors. > > So in summary, at least for a DWC3 based subsystem, the only way to > reproduce it is if there is a way to dynamically switch the DWC3 core > max speed parameter. Could it be that you have a bug in your out-of-tree changes? Perhaps there's some assumption which your changes aren't guaranteeing. -- balbi
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