Re: [PATCH] usb: Clear both buffers when clearing a control transferTT buffer.

[Alan Stern]

On Thu, 27 Jun 2013, William Gulland wrote:

>     Control transfers have both IN and OUT (or SETUP) packets, so when
>     clearing TT buffers for a control transfer it's necessary to send
>     two HUB_CLEAR_TT_BUFFER requests to the hub.

What makes you think this is necessary?  Have you found any hardware 
that requires this?

Although the USB spec doesn't say much about Clear-TT-Buffer requests,
the text in section 11.17.1 and Figure 11-47 seems to indicate that a
second Clear-TT-Buffer shouldn't be needed.  The spec says that TT
buffers are matched based on the device address, endpoint number, and
endpoint direction -- but the direction is used only for bulk
endpoints, not for control endpoints.

In particular, a control endpoint uses only one TT buffer for both the
IN and OUT directions.  So I don't think two Clear-TT-Buffers are
needed.

Alan Stern

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