linux-kernel - Re: [PATCH v4 1/1] usb: xhci: Add Clear_TT

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Date:   Mon, 6 May 2019 10:57:48 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Jim Lin <jilin@...dia.com>
cc:     gregkh@...uxfoundation.org, <mathias.nyman@...el.com>,
        <hminas@...opsys.com>, <kai.heng.feng@...onical.com>,
        <drinkcat@...omium.org>, <prime.zeng@...ilicon.com>,
        <malat@...ian.org>, <nsaenzjulienne@...e.de>, <jflat@...omium.org>,
        <linus.walleij@...aro.org>, <clabbe@...libre.com>,
        <colin.king@...onical.com>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/1] usb: xhci: Add Clear_TT_Buffer

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,
> like Set_Interface.
> 
> 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
> for XHCI.

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 
controller.

Alan Stern