From: William Gulland <wgulland@xxxxxxxxxx> Date: Fri, Jun 28, 2013 at 3:13 PM Subject: Re: [PATCH] usb: Clear both buffers when clearing a control transfer TT buffer. To: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Cc: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx>, USB list <linux-usb@xxxxxxxxxxxxxxx> On Fri, Jun 28, 2013 at 12:24 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > Please use Reply-To-All so that your response gets sent to the mailing > list as well as to me. And please don't top-post. > > On Fri, 28 Jun 2013, William Gulland wrote: > > > Yes, two ClearTTBuffer requests seem to be necessary with Intel's CaveCreek > > integrated rate-matching hub - I've got it into the state where control > > requests to a USB 1.1 device were failing, > > How did you manage to do that? > > > but recovered when I sent the > > hub a ClearTTBuffer for endpoint 0 - but only if I set the IN bit in the > > request. > > This sounds like a bug in the Intel hub hardware, or at least, > unintentional behavior. > > Sarah, is this the sort of thing the Intel engineers would want to know > about? > > > William > > > > > > On Fri, Jun 28, 2013 at 8:56 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>wrote: > > > > > 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 > I got the hub into the bad state by continually opening/doing I/O/closing with three cdc-acm serial devices - it only seems to happen with at least three devices running simultaneously on the same hub, and takes a long time (hours) to go wrong. William (posting again in plaintext) -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
