Re: [PATCH] usb: xhci: Make usb_host_endpoint.hcpriv survive endpoint_disable()

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 4/1/26 17:52, Michal Pecio wrote:
> On Wed, 1 Apr 2026 17:34:37 +0300, Mathias Nyman wrote:
>> On 3/31/26 02:06, Michal Pecio wrote:
>>> xHCI hardware maintains its endpoint state between add_endpoint()
>>> and drop_endpoint() calls followed by successful check_bandwidth().
>>> So does the driver.
>>>
>>> Core may call endpoint_disable() during xHCI endpoint life, so don't
>>> clear host_ep->hcpriv then, because this breaks endpoint_reset().
>>>
>>> If a driver calls usb_set_interface(), submits URBs which make host
>>> sequence state non-zero and calls usb_clear_halt(), the device clears
>>> its sequence state but xhci_endpoint_reset() bails out. The next URB
>>> malfunctions: USB2 loses one packet, USB3 gets Transaction Error or
>>> may not complete at all on some (buggy?) HCs from ASMedia and AMD.
>>> This is triggered by uvcvideo on bulk video devices.
>>
>> Were you able to trigger a usb_clear_halt() called with ep->hcpriv == NULL,
>> causing a toggle/seq mismatch?
>>
>> The ep->hcpriv should be set back correctly in usb_set_interface():
>>
>> usb_set_interface()
>>     usb_hcd_alloc_bandwidth()
>>       hcd->driver->add_endpoint()
>>         xhci_add_endpoint()
>>           ep->hcpriv = udev;
> 
> right, and later:
> 
>       usb_disable_interface(dev, iface, true)
>         usb_disable_endpoint(dev, ..., true)
>           usb_hcd_disable_endpoint(dev, ep)
>             hcd->driver->endpoint_disable(hcd, ep)
>       usb_enable_interface(dev, iface, true)
>         usb_enable_endpoint(dev, ..., true)
>           usb_hcd_reset_endpoint(dev, ep)
>             hcd->driver->endpoint_reset(hcd, ep)
> 

True, thanks, usb_set_interface() calls usb_disable_interface() twice.
First time just to flush pending URBs, second time with reset_hardware
flag set.

Adding patch to queue

-Mathias