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SubjectRe: [PATCH] usb: Clear both buffers when clearing a control transfer TT buffer.
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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