On 4/24/2021 1:05 AM, Felipe Balbi wrote: > > 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. > Hi Felipe, Unless there is a limitation on how the USB gadget max speed can be used, i.e. the USB gadget max speed MUST stay the same throughout a device's boot period, then our out of tree changes may have the wrong assumptions. However, I don't see that stated anywhere, and I still feel the current usb_assign_descriptors() and usb_free_all_descriptors() aren't aligned with one another. One API decides which descriptors to copy based on a parameter, whereas the other just frees all of them irrespective. Thanks Wesley Cheng -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
