Messages in this thread | | | Date | Fri, 28 Jun 2013 11:56:26 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH] usb: Clear both buffers when clearing a control transfer TT buffer. |
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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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