Hi, Wesley Cheng <wcheng@xxxxxxxxxxxxxx> writes: > 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 no, not throughout boot, but it can't change while the device is enumerated. > 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. that's a valid point. -- balbi
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