linux-stable.git/drivers/usb/host, branch v3.12.13 Linux kernel stable tree Revert "usb: xhci: Link TRB must not occur within a USB payload burst" 2014-02-22T21:32:28+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2014-01-31T19:52:57+00:00 aad850bd0d8be9038f887bae8b76ac81da6ddd2a commit 3d4b81eda2211f32886e2978daf6f39885042fc4 upstream. This reverts commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e. It's a hack that caused regressions in the usb-storage and userspace USB drivers that use usbfs and libusb. Commit 70cabb7d992f "xhci 1.0: Limit arbitrarily-aligned scatter gather." should fix the issues seen with the ax88179_178a driver on xHCI 1.0 hosts, without causing regressions. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 3d4b81eda2211f32886e2978daf6f39885042fc4 upstream.

This reverts commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e.  It's a
hack that caused regressions in the usb-storage and userspace USB
drivers that use usbfs and libusb.  Commit 70cabb7d992f "xhci 1.0: Limit
arbitrarily-aligned scatter gather." should fix the issues seen with the
ax88179_178a driver on xHCI 1.0 hosts, without causing regressions.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Revert "xhci: Avoid infinite loop when sg urb requires too many trbs" 2014-02-22T21:32:28+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2014-01-31T19:51:59+00:00 f47a7fb0a06f44707d416b752508d79ce59575e5 commit 9cf00d91708221ff2d8a11143315f7ebab8d5da8 upstream. This reverts commit d6c9ea9069af684358efedcaf2f2f687f51c58ee. We are ripping out commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e "usb: xhci: Link TRB must not occur within a USB payload burst" because it's a hack that caused regressions in the usb-storage and userspace USB drivers that use usbfs and libusb. This commit attempted to fix the issues with that patch. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 9cf00d91708221ff2d8a11143315f7ebab8d5da8 upstream.

This reverts commit d6c9ea9069af684358efedcaf2f2f687f51c58ee.

We are ripping out commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e "usb:
xhci: Link TRB must not occur within a USB payload burst" because it's a
hack that caused regressions in the usb-storage and userspace USB
drivers that use usbfs and libusb.  This commit attempted to fix the
issues with that patch.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Revert "xhci: Set scatter-gather limit to avoid failed block writes." 2014-02-22T21:32:28+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2014-01-31T19:45:02+00:00 563f01094b4a1b860521b156f233d7292a7b9d57 commit 1386ff75797a187df324062fb4e929152392da88 upstream. This reverts commit f2d9b991c549f159dc9ae81f77d8206c790cbfee. We are ripping out commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e "usb: xhci: Link TRB must not occur within a USB payload burst" because it's a hack that caused regressions in the usb-storage and userspace USB drivers that use usbfs and libusb. This commit attempted to fix the issues with that patch. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 1386ff75797a187df324062fb4e929152392da88 upstream.

This reverts commit f2d9b991c549f159dc9ae81f77d8206c790cbfee.

We are ripping out commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e "usb:
xhci: Link TRB must not occur within a USB payload burst" because it's a
hack that caused regressions in the usb-storage and userspace USB
drivers that use usbfs and libusb.  This commit attempted to fix the
issues with that patch.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
xhci 1.0: Limit arbitrarily-aligned scatter gather. 2014-02-22T21:32:28+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2014-01-31T19:26:25+00:00 d6472e8a66fb882548361ddbf96de6db00f3c2b3 commit 247bf557273dd775505fb9240d2d152f4f20d304 upstream. xHCI 1.0 hosts have a set of requirements on how to align transfer buffers on the endpoint rings called "TD fragment" rules. When the ax88179_178a driver added support for scatter gather in 3.12, with commit 804fad45411b48233b48003e33a78f290d227c8 "USBNET: ax88179_178a: enable tso if usb host supports sg dma", it broke the device under xHCI 1.0 hosts. Under certain network loads, the device would see an unexpected short packet from the host, which would cause the device to stop sending ethernet packets, even through USB packets would still be sent. Commit 35773dac5f86 "usb: xhci: Link TRB must not occur within a USB payload burst" attempted to fix this. It was a quick hack to partially implement the TD fragment rules. However, it caused regressions in the usb-storage layer and userspace USB drivers using libusb. The patches to attempt to fix this are too far reaching into the USB core, and we really need to implement the TD fragment rules correctly in the xHCI driver, instead of continuing to wallpaper over the issues. Disable arbitrarily-aligned scatter-gather in the xHCI driver for 1.0 hosts. Only the ax88179_178a driver checks the no_sg_constraint flag, so don't set it for 1.0 hosts. This should not impact usb-storage or usbfs behavior, since they pass down max packet sized aligned sg-list entries (512 for USB 2.0 and 1024 for USB 3.0). Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Tested-by: Mark Lord <mlord@pobox.com> Cc: David Laight <David.Laight@ACULAB.COM> Cc: Bjørn Mork <bjorn@mork.no> Cc: Freddy Xin <freddy@asix.com.tw> Cc: Ming Lei <ming.lei@canonical.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 247bf557273dd775505fb9240d2d152f4f20d304 upstream.

xHCI 1.0 hosts have a set of requirements on how to align transfer
buffers on the endpoint rings called "TD fragment" rules.  When the
ax88179_178a driver added support for scatter gather in 3.12, with
commit 804fad45411b48233b48003e33a78f290d227c8 "USBNET: ax88179_178a:
enable tso if usb host supports sg dma", it broke the device under xHCI
1.0 hosts.  Under certain network loads, the device would see an
unexpected short packet from the host, which would cause the device to
stop sending ethernet packets, even through USB packets would still be
sent.

Commit 35773dac5f86 "usb: xhci: Link TRB must not occur within a USB
payload burst" attempted to fix this.  It was a quick hack to partially
implement the TD fragment rules.  However, it caused regressions in the
usb-storage layer and userspace USB drivers using libusb.  The patches
to attempt to fix this are too far reaching into the USB core, and we
really need to implement the TD fragment rules correctly in the xHCI
driver, instead of continuing to wallpaper over the issues.

Disable arbitrarily-aligned scatter-gather in the xHCI driver for 1.0
hosts.  Only the ax88179_178a driver checks the no_sg_constraint flag,
so don't set it for 1.0 hosts.  This should not impact usb-storage or
usbfs behavior, since they pass down max packet sized aligned sg-list
entries (512 for USB 2.0 and 1024 for USB 3.0).

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Tested-by: Mark Lord <mlord@pobox.com>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Bjørn Mork <bjorn@mork.no>
Cc: Freddy Xin <freddy@asix.com.tw>
Cc: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
xhci: Set scatter-gather limit to avoid failed block writes. 2014-02-06T19:22:17+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2014-01-06T21:07:03+00:00 201a3fa8b289b490886aa3f5cf508af165152a42 commit f2d9b991c549f159dc9ae81f77d8206c790cbfee upstream. Commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e "usb: xhci: Link TRB must not occur within a USB payload burst" attempted to fix an issue found with USB ethernet adapters, and inadvertently broke USB storage devices. The patch attempts to ensure that transfers never span a segment, and rejects transfers that have more than 63 entries (or possibly less, if some entries cross 64KB boundaries). usb-storage limits the maximum transfer size to 120K, and we had assumed the block layer would pass a scatter-gather list of 4K entries, resulting in no more than 31 sglist entries: http://marc.info/?l=linux-usb&m=138498190419312&w=2 That assumption was wrong, since we've seen the driver reject a write that was 218 sectors long (of probably 512 bytes each): Jan 1 07:04:49 jidanni5 kernel: [ 559.624704] xhci_hcd 0000:00:14.0: Too many fragments 79, max 63 ... Jan 1 07:04:58 jidanni5 kernel: [ 568.622583] Write(10): 2a 00 00 06 85 0e 00 00 da 00 Limit the number of scatter-gather entries to half a ring segment. That should be margin enough in case some entries cross 64KB boundaries. Increase the number of TRBs per segment from 64 to 256, which should result in ring segments fitting on a 4K page. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Reported-by: jidanni@jidanni.org References: http://bugs.debian.org/733907 Fixes: 35773dac5f86 ('usb: xhci: Link TRB must not occur within a USB payload burst') Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit f2d9b991c549f159dc9ae81f77d8206c790cbfee upstream.

Commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e "usb: xhci: Link TRB
must not occur within a USB payload burst" attempted to fix an issue
found with USB ethernet adapters, and inadvertently broke USB storage
devices.  The patch attempts to ensure that transfers never span a
segment, and rejects transfers that have more than 63 entries (or
possibly less, if some entries cross 64KB boundaries).

usb-storage limits the maximum transfer size to 120K, and we had assumed
the block layer would pass a scatter-gather list of 4K entries,
resulting in no more than 31 sglist entries:

http://marc.info/?l=linux-usb&m=138498190419312&w=2

That assumption was wrong, since we've seen the driver reject a write
that was 218 sectors long (of probably 512 bytes each):

Jan  1 07:04:49 jidanni5 kernel: [  559.624704] xhci_hcd 0000:00:14.0: Too many fragments 79, max 63
...
Jan  1 07:04:58 jidanni5 kernel: [  568.622583] Write(10): 2a 00 00 06 85 0e 00 00 da 00

Limit the number of scatter-gather entries to half a ring segment.  That
should be margin enough in case some entries cross 64KB boundaries.
Increase the number of TRBs per segment from 64 to 256, which should
result in ring segments fitting on a 4K page.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-by: jidanni@jidanni.org
References: http://bugs.debian.org/733907
Fixes: 35773dac5f86 ('usb: xhci: Link TRB must not occur within a USB payload burst')
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
xhci: Avoid infinite loop when sg urb requires too many trbs 2014-02-06T19:22:17+00:00 Ben Hutchings ben@decadent.org.uk 2014-01-06T03:16:32+00:00 c7104ed26ac349d1ed2e7d9b8716100823477ab4 commit d6c9ea9069af684358efedcaf2f2f687f51c58ee upstream. Currently prepare_ring() returns -ENOMEM if the urb won't fit into a single ring segment. usb_sg_wait() treats this error as a temporary condition and will keep retrying until something else goes wrong. The number of retries should be limited in usb_sg_wait(), but also prepare_ring() should not return an error code that suggests it might be worth retrying. Change it to -EINVAL. Reported-by: jidanni@jidanni.org References: http://bugs.debian.org/733907 Fixes: 35773dac5f86 ('usb: xhci: Link TRB must not occur within a USB payload burst') Signed-off-by: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit d6c9ea9069af684358efedcaf2f2f687f51c58ee upstream.

Currently prepare_ring() returns -ENOMEM if the urb won't fit into a
single ring segment.  usb_sg_wait() treats this error as a temporary
condition and will keep retrying until something else goes wrong.

The number of retries should be limited in usb_sg_wait(), but also
prepare_ring() should not return an error code that suggests it might
be worth retrying.  Change it to -EINVAL.

Reported-by: jidanni@jidanni.org
References: http://bugs.debian.org/733907
Fixes: 35773dac5f86 ('usb: xhci: Link TRB must not occur within a USB payload burst')
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
usb: ehci: add freescale imx28 special write register method 2014-02-06T19:22:15+00:00 Peter Chen peter.chen@freescale.com 2014-01-10T05:51:26+00:00 f5a67eedd6c513de2cd707ab2015e1154119d74b commit feffe09f510c475df082546815f9e4a573f6a233 upstream. According to Freescale imx28 Errata, "ENGR119653 USB: ARM to USB register error issue", All USB register write operations must use the ARM SWP instruction. So, we implement a special ehci_write for imx28. Discussion for it at below: http://marc.info/?l=linux-usb&m=137996395529294&w=2 Without this patcheset, imx28 works unstable at high AHB bus loading. If the bus loading is not high, the imx28 usb can work well at the most of time. There is a IC errata for this problem, usually, we consider IC errata is a problem not a new feature, and this workaround is needed for that, so we need to add them to stable tree 3.11+. Cc: robert.hodaszi@digi.com Signed-off-by: Peter Chen <peter.chen@freescale.com> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de> Tested-by: Marc Kleine-Budde <mkl@pengutronix.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit feffe09f510c475df082546815f9e4a573f6a233 upstream.

According to Freescale imx28 Errata, "ENGR119653 USB: ARM to USB
register error issue", All USB register write operations must
use the ARM SWP instruction. So, we implement a special ehci_write
for imx28.

Discussion for it at below:
http://marc.info/?l=linux-usb&m=137996395529294&w=2

Without this patcheset, imx28 works unstable at high AHB bus loading.
If the bus loading is not high, the imx28 usb can work well at the most
of time. There is a IC errata for this problem, usually, we consider
IC errata is a problem not a new feature, and this workaround is needed
for that, so we need to add them to stable tree 3.11+.

Cc: robert.hodaszi@digi.com
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Tested-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
usb: xhci: Check for XHCI_PLAT in xhci_cleanup_msix() 2014-02-06T19:22:15+00:00 Jack Pham jackp@codeaurora.org 2013-11-15T22:53:14+00:00 494a99a553c3362e18fc9d0687dbd495f7942f83 commit 9005355af23856c55a5538c9024355785424821b upstream. If CONFIG_PCI is enabled, make sure xhci_cleanup_msix() doesn't try to free a bogus PCI IRQ or dereference an invalid pci_dev when the xHCI device is actually a platform_device. This patch should be backported to kernels as old as 3.9, that contain the commit 52fb61250a7a132b0cfb9f4a1060a1f3c49e5a25 "xhci-plat: Don't enable legacy PCI interrupts." Signed-off-by: Jack Pham <jackp@codeaurora.org> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 9005355af23856c55a5538c9024355785424821b upstream.

If CONFIG_PCI is enabled, make sure xhci_cleanup_msix()
doesn't try to free a bogus PCI IRQ or dereference an invalid
pci_dev when the xHCI device is actually a platform_device.

This patch should be backported to kernels as old as 3.9, that
contain the commit 52fb61250a7a132b0cfb9f4a1060a1f3c49e5a25
"xhci-plat: Don't enable legacy PCI interrupts."

Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
xhci: Limit the spurious wakeup fix only to HP machines 2014-01-09T20:25:08+00:00 Takashi Iwai tiwai@suse.de 2013-12-09T13:53:36+00:00 0d1ffc541943dd3133615d8a5b21549b25c58751 commit 6962d914f317b119e0db7189199b21ec77a4b3e0 upstream. We've got regression reports that my previous fix for spurious wakeups after S5 on HP Haswell machines leads to the automatic reboot at shutdown on some machines. It turned out that the fix for one side triggers another BIOS bug in other side. So, it's exclusive. Since the original S5 wakeups have been confirmed only on HP machines, it'd be safer to apply it only to limited machines. As a wild guess, limiting to machines with HP PCI SSID should suffice. This patch should be backported to kernels as old as 3.12, that contain the commit 638298dc66ea36623dbc2757a24fc2c4ab41b016 "xhci: Fix spurious wakeups after S5 on Haswell". Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=66171 Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Tested-by: <dashing.meng@gmail.com> Reported-by: Niklas Schnelle <niklas@komani.de> Reported-by: Giorgos <ganastasiouGR@gmail.com> Reported-by: <art1@vhex.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 6962d914f317b119e0db7189199b21ec77a4b3e0 upstream.

We've got regression reports that my previous fix for spurious wakeups
after S5 on HP Haswell machines leads to the automatic reboot at
shutdown on some machines.  It turned out that the fix for one side
triggers another BIOS bug in other side.  So, it's exclusive.

Since the original S5 wakeups have been confirmed only on HP machines,
it'd be safer to apply it only to limited machines.  As a wild guess,
limiting to machines with HP PCI SSID should suffice.

This patch should be backported to kernels as old as 3.12, that
contain the commit 638298dc66ea36623dbc2757a24fc2c4ab41b016 "xhci: Fix
spurious wakeups after S5 on Haswell".

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=66171
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Tested-by: <dashing.meng@gmail.com>
Reported-by: Niklas Schnelle <niklas@komani.de>
Reported-by: Giorgos <ganastasiouGR@gmail.com>
Reported-by: <art1@vhex.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
usb: xhci: Link TRB must not occur within a USB payload burst 2013-12-20T15:48:55+00:00 David Laight David.Laight@ACULAB.COM 2013-11-11T12:26:54+00:00 459d3c14611784bc5155cc622536b2b0f0740aa2 commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e upstream. Section 4.11.7.1 of rev 1.0 of the xhci specification states that a link TRB can only occur at a boundary between underlying USB frames (512 bytes for high speed devices). If this isn't done the USB frames aren't formatted correctly and, for example, the USB3 ethernet ax88179_178a card will stop sending (while still receiving) when running a netperf tcp transmit test with (say) and 8k buffer. This should be a candidate for stable, the ax88179_178a driver defaults to gso and tso enabled so it passes a lot of fragmented skb to the USB stack. Notes from Sarah: Discussion: http://marc.info/?l=linux-usb&m=138384509604981&w=2 This patch fixes a long-standing xHCI driver bug that was revealed by a change in 3.12 in the usb-net driver. Commit 638c5115a794981441246fa8fa5d95c1875af5ba "USBNET: support DMA SG" added support to use bulk endpoint scatter-gather (urb->sg). Only the USB ethernet drivers trigger this bug, because the mass storage driver sends sg list entries in page-sized chunks. This patch only fixes the issue for bulk endpoint scatter-gather. The problem will still occur for periodic endpoints, because hosts will interpret no-op transfers as a request to skip a service interval, which is not what we want. Luckily, the USB core isn't set up for scatter-gather on isochronous endpoints, and no USB drivers use scatter-gather for interrupt endpoints. Document this known limitation so that developers won't try to use urb->sg for interrupt endpoints until this issue is fixed. The more comprehensive fix would be to allow link TRBs in the middle of the endpoint ring and revert this patch, but that fix would touch too much code to be allowed in for stable. This patch should be backported to kernels as old as 3.12, that contain the commit 638c5115a794981441246fa8fa5d95c1875af5ba "USBNET: support DMA SG". Without this patch, the USB network device gets wedged, and stops sending packets. Mark Lord confirms this patch fixes the regression: http://marc.info/?l=linux-netdev&m=138487107625966&w=2 Signed-off-by: David Laight <david.laight@aculab.com> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Tested-by: Mark Lord <mlord@pobox.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 35773dac5f862cb1c82ea151eba3e2f6de51ec3e upstream.

Section 4.11.7.1 of rev 1.0 of the xhci specification states that a link TRB
can only occur at a boundary between underlying USB frames (512 bytes for
high speed devices).

If this isn't done the USB frames aren't formatted correctly and, for example,
the USB3 ethernet ax88179_178a card will stop sending (while still receiving)
when running a netperf tcp transmit test with (say) and 8k buffer.

This should be a candidate for stable, the ax88179_178a driver defaults to
gso and tso enabled so it passes a lot of fragmented skb to the USB stack.

Notes from Sarah:

Discussion: http://marc.info/?l=linux-usb&m=138384509604981&w=2

This patch fixes a long-standing xHCI driver bug that was revealed by a
change in 3.12 in the usb-net driver.  Commit
638c5115a794981441246fa8fa5d95c1875af5ba "USBNET: support DMA SG" added
support to use bulk endpoint scatter-gather (urb->sg).  Only the USB
ethernet drivers trigger this bug, because the mass storage driver sends
sg list entries in page-sized chunks.

This patch only fixes the issue for bulk endpoint scatter-gather.  The
problem will still occur for periodic endpoints, because hosts will
interpret no-op transfers as a request to skip a service interval, which
is not what we want.

Luckily, the USB core isn't set up for scatter-gather on isochronous
endpoints, and no USB drivers use scatter-gather for interrupt
endpoints.  Document this known limitation so that developers won't try
to use urb->sg for interrupt endpoints until this issue is fixed.  The
more comprehensive fix would be to allow link TRBs in the middle of the
endpoint ring and revert this patch, but that fix would touch too much
code to be allowed in for stable.

This patch should be backported to kernels as old as 3.12, that contain
the commit 638c5115a794981441246fa8fa5d95c1875af5ba "USBNET: support DMA
SG".  Without this patch, the USB network device gets wedged, and stops
sending packets.  Mark Lord confirms this patch fixes the regression:

http://marc.info/?l=linux-netdev&m=138487107625966&w=2

Signed-off-by: David Laight <david.laight@aculab.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Tested-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>