Commit c2f6595f authored Nov 18, 2009 by Alan Stern Committed by Greg Kroah-Hartman Nov 30, 2009

USB: EHCI: don't send Clear-TT-Buffer following a STALL



This patch (as1304) fixes a regression in ehci-hcd.  Evidently some
hubs don't handle Clear-TT-Buffer requests correctly, so we should
avoid sending them when they don't appear to be absolutely necessary.
The reported symptom is that output on a downstream audio device cuts
out because the hub stops relaying isochronous packets.

The patch prevents Clear-TT-Buffer requests from being sent following
a STALL handshake.  In theory a STALL indicates either that the
downstream device sent a STALL or that no matching TT buffer could be
found.  In either case, the transfer is completed and the TT buffer
does not remain busy, so it doesn't need to be cleared.

Also, the patch fixes a minor flaw in the code that actually sends the
Clear-TT-Buffer requests.  Although the pipe direction isn't really
used for control transfers, it should be a Send rather than a Receive.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Javier Kohen <jkohen@users.sourceforge.net>
CC: David Brownell <david-b@pacbell.net>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

parent a8a84540

drivers/usb/core/hub.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -444,7 +444,7 @@ resubmit:
		static inline int
		hub_clear_tt_buffer (struct usb_device *hdev, u16 devinfo, u16 tt)
		{
		return usb_control_msg(hdev, usb_rcvctrlpipe(hdev, 0),
		return usb_control_msg(hdev, usb_sndctrlpipe(hdev, 0),
		HUB_CLEAR_TT_BUFFER, USB_RT_PORT, devinfo,
		tt, NULL, 0, 1000);
		}

drivers/usb/host/ehci-q.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -487,8 +487,20 @@ halt:
		* we must clear the TT buffer (11.17.5).
		*/
		if (unlikely(last_status != -EINPROGRESS &&
		last_status != -EREMOTEIO))
		ehci_clear_tt_buffer(ehci, qh, urb, token);
		last_status != -EREMOTEIO)) {
		/* The TT's in some hubs malfunction when they
		* receive this request following a STALL (they
		* stop sending isochronous packets). Since a
		* STALL can't leave the TT buffer in a busy
		* state (if you believe Figures 11-48 - 11-51
		* in the USB 2.0 spec), we won't clear the TT
		* buffer in this case. Strictly speaking this
		* is a violation of the spec.
		*/
		if (last_status != -EPIPE)
		ehci_clear_tt_buffer(ehci, qh, urb,
		token);
		}
		}

		/* if we're removing something not at the queue head,

Admin message