[3.16.y-ckt stable] Patch "xhci: Solve full event ring by increasing TRBS_PER_SEGMENT to 256" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    xhci: Solve full event ring by increasing TRBS_PER_SEGMENT to 256

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt13.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From b20acddad11c518c0b2b25a87cd170cfbeee67c6 Mon Sep 17 00:00:00 2001
From: Mathias Nyman <mathias.nyman at linux.intel.com>
Date: Thu, 30 Apr 2015 17:16:03 +0300
Subject: xhci: Solve full event ring by increasing TRBS_PER_SEGMENT to 256

commit 18cc2f4cbbaf825a4fedcf2d60fd388d291e0a38 upstream.

Our event ring consists of only one segment, and we risk filling
the event ring in case we get isoc transfers with short intervals
such as webcams that fill a TD every microframe (125us)

With 64 TRB segment size one usb camera could fill the event ring in 8ms.
A setup with several cameras and other devices can fill up the
event ring as it is shared between all devices.
This has occurred when uvcvideo queues 5 * 32TD URBs which then
get cancelled when the video mode changes. The cancelled URBs are returned
in the xhci interrupt context and blocks the interrupt handler from
handling the new events.

A full event ring will block xhci from scheduling traffic and affect all
devices conneted to the xhci, will see errors such as Missed Service
Intervals for isoc devices, and  and Split transaction errors for LS/FS
interrupt devices.

Increasing the TRB_PER_SEGMENT will also increase the default endpoint ring
size, which is welcome as for most isoc transfer we had to dynamically
expand the endpoint ring anyway to be able to queue the 5 * 32TDs uvcvideo
queues.

The default size used to be 64 TRBs per segment

Signed-off-by: Mathias Nyman <mathias.nyman at linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/usb/host/xhci.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index d40a72b69f26..a70e45c7c440 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1267,7 +1267,7 @@ union xhci_trb {
  * since the command ring is 64-byte aligned.
  * It must also be greater than 16.
  */
-#define TRBS_PER_SEGMENT	64
+#define TRBS_PER_SEGMENT	256
 /* Allow two commands + a link TRB, along with any reserved command TRBs */
 #define MAX_RSVD_CMD_TRBS	(TRBS_PER_SEGMENT - 3)
 #define TRB_SEGMENT_SIZE	(TRBS_PER_SEGMENT*16)