linux-kernel - Re: [PATCH] usb: Clear both buffers when clearing a control transfer TT buffer.

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Message-ID: <Pine.LNX.4.44L0.1307011636530.1547-100000@iolanthe.rowland.org>
Date:	Mon, 1 Jul 2013 16:41:17 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	William Gulland <wgulland@...gle.com>
cc:	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Lan Tianyu <tianyu.lan@...el.com>,
	Ming Lei <ming.lei@...onical.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [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.
> 
> Signed-off-by: William Gulland <wgulland@...gle.com>
> ---
>  drivers/usb/core/hub.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index feef935..868ad74 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -668,6 +668,15 @@ resubmit:
>  static inline int
>  hub_clear_tt_buffer (struct usb_device *hdev, u16 devinfo, u16 tt)
>  {
> +	/* Need to clear both directions for control ep */
> +	if (((devinfo >> 11) & USB_ENDPOINT_XFERTYPE_MASK) ==
> +			USB_ENDPOINT_XFER_CONTROL) {
> +		int status = usb_control_msg(hdev, usb_sndctrlpipe(hdev, 0),
> +				HUB_CLEAR_TT_BUFFER, USB_RT_PORT,
> +				devinfo ^ 0x8000, tt, NULL, 0, 1000);
> +		if (status)
> +			return status;
> +	}
>  	return usb_control_msg(hdev, usb_sndctrlpipe(hdev, 0),
>  			       HUB_CLEAR_TT_BUFFER, USB_RT_PORT, devinfo,
>  			       tt, NULL, 0, 1000);

Well, this won't hurt much.  And since it does seem to fix a hardware
problem,

Acked-by: Alan Stern <stern@...land.harvard.edu>

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