On Mon, 6 May 2019, Jim Lin wrote:
USB 2.0 specification chapter 11.17.5 says "as part of endpoint halt
processing for full-/low-speed endpoints connected via a TT, the host
software must use the Clear_TT_Buffer request to the TT to ensure
that the buffer is not in the busy state".
In our case, a full-speed speaker (ConferenceCam) is behind a high-
speed hub (ConferenceCam Connect), sometimes once we get STALL on a
request we may continue to get STALL with the folllowing requests,
Here we add Clear_TT_Buffer for the following Set_Interface requests
to get ACK successfully.
Originally usb_hub_clear_tt_buffer uses urb->dev->devnum as device
address while sending Clear_TT_Buffer command, but this doesn't work
Why doesn't it work for xHCI? Clear-TT-Buffer is part of the USB 2.0
spec; it should work exactly the same for xHCI as for a USB-2.0 host