This patch (as1380) fixes a bug in the wakeup settings for EHCI host
controllers.  When the controller is suspended, if it isn't enabled
for remote wakeup then we have to turn off all the port wakeup flags.
Disabling PCI PME# isn't good enough, because some systems (Intel)
evidently use alternate wakeup signalling paths.

In addition, the patch improves the handling of the Intel Moorestown
hardware by performing various power-up and power-down delays just
once instead of once for each port (i.e., the delays are moved outside
of the port loops).  This requires extra code, but the total delay
time is reduced.

There are also a few additional minor cleanups.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Reported-by: NOndrej Zary <linux@rainbow-software.org>
CC: Alek Du <alek.du@intel.com>
CC: stable <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1348) removes the bogus
USB_PORT_FEAT_{HIGHSPEED,SUPERSPEED} symbols from ch11.h.  No such
features are defined by the USB spec.  (There is a PORT_LOWSPEED
feature, but the spec doesn't mention it except to say that host
software should never use it.)  The speed indicators are port
statuses, not port features.

As a temporary workaround for the xhci-hcd driver, a fictional
USB_PORT_STAT_SUPER_SPEED symbol is added.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
CC: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1369) fixes a problem in ehci-hcd.  Some controllers
occasionally run into trouble when the driver reclaims siTDs too
quickly.  This can happen while streaming audio; it causes the
controller to crash.

The patch changes siTD reclamation to work the same way as iTD
reclamation: Completed siTDs are stored on a list and not reused until
at least one frame has passed.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Tested-by: NNate Case <ncase@xes-inc.com>
CC: <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The EHCI driver stores in usb_host_endpoint.hcpriv a pointer to either
an ehci_qh or an ehci_iso_stream structure, and uses the contents of the
hw_info1 field to distinguish the two cases.

After ehci_qh was split into hw and sw parts, ehci_iso_stream must also
be adjusted so that it again looks like an ehci_qh structure.

This fixes a NULL pointer access in ehci_endpoint_disable() when it
tries to access qh->hw->hw_info1.
Signed-off-by: NClemens Ladisch <clemens@ladisch.de>
Reported-by: NColin Fletcher <colin.m.fletcher@googlemail.com>
Cc: stable <stable@kernel.org>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

a quirky chipset needs periodic schedules to run for a minimum
time before they can be disabled again. This enforces the requirement
with a time stamp and a calculated delay
Signed-off-by: NOliver Neukum <oliver@neukum.org>
Cc: stable <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1280) fixes an obscure bug in ehci-hcd's dequeuing logic
for async URBs.  If a later URB is unlinked and the completion
routine unlinks an earlier URB, then the earlier URB won't be given
back in a timely manner because the endpoint queue isn't rescanned as
it should be.

Similar bugs occur if an endpoint is reset or a halt is cleared while
a completion routine is running, because the subroutines don't test
for the COMPLETING state.

All these problems are solved by adding a new needs_rescan flag to the
ehci_qh structure.  If the flag is set while scanning through an idle
QH, the scan will be repeated.  If the QH isn't idle then an unlink
cycle will be initiated, and the proper action will be taken when it
becomes idle.

Also, an unnecessary test is removed from qh_link_async(): That
routine is never called if the QH's state isn't IDLE.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
CC: David Brownell <david-b@pacbell.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The Intel Moorestown EHCI controller supports non-standard HOSTPCx register
extension. This register controls the LPM behaviour and controls the behaviour
of each USB port.
Signed-off-by: NJacob Pan <jacob.jun.pan@intel.com>
Signed-off-by: NAlek Du <alek.du@intel.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The ehci_qh structure merged hw and sw together which is not good:
1. More and more items are being added into ehci_qh, the ehci_qh software
   part are unnecessary to be allocated in DMA qh_pool.
2. If HCD has local SRAM, the sw part will consume it too, and it won't
   bring any benefit.
3. For non-cache-coherence system, the entire ehci_qh is uncachable, actually
   we only need the hw part to be uncacheable. Spliting them will let the sw
   part to be cacheable.
Signed-off-by: NAlek Du <alek.du@intel.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
CC: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Basically the io watchdog is only useful for those quirk HCDs. For most
good ones, it only brings unnecessary wakeups.  At least, I know the
Intel EHCI HCDs should turn off the flag.
Signed-off-by: NAlek Du <alek.du@intel.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

trivial: fix typo "for for" in multiple files
Signed-off-by: NAnand Gadiyar <gadiyar@ti.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

This patch (as1256) changes ehci-hcd and all the other drivers in the
EHCI family to make use of the new clear_tt_buffer callbacks.  When a
Clear-TT-Buffer request is in progress for a QH, the QH is not allowed
to be linked into the async schedule until the request is finished.
At that time, if there are any URBs queued for the QH, it is linked
into the async schedule.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1243) tries to improve ehci-hcd's scheduling of
interrupt transfers.  Instead of trying to cram all transfers with the
same period into the same frame, the new code will spread the
transfers out among lots of different frames.  This should reduce the
periodic schedule load in any one frame -- some host controllers have
trouble when there's too much work to do.

A more thorough approach would stagger the uframe values as well.  But
this is enough to make a big improvement.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Tested-by: NDwayne Fontenot <dwayne.fontenot@att.net>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The base versions handle constant folding now.
Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1204) adds a software retry mechanism to ehci-hcd.  It
gets invoked when the driver encounters transaction errors on an
asynchronous endpoint.  On many systems, hardware deficiencies cause
such errors to occur if one device is unplugged while the host is
communicating with another device.  With the patch, the failed
transactions are retried and generally succeed the second or third
time through.

This is based on code originally written by Koichiro Saito.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Tested by: Koichiro Saito <Saito.Koichiro@adniss.jp>
CC: David Brownell <david-b@pacbell.net>
Cc: stable <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1205) moves timer_action() from ehci.h to ehci-hcd.c and
makes it out-of-line.  Over the years it has grown too big to be inline
any more.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Acked-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Currently ITDs are immediately recycled whenever their URB completes.
However, EHCI hardware can sometimes remember some ITD state.  This
means that when the ITD is reused before end-of-frame it may sometimes
cause the hardware to reference bogus state.

This patch defers reusing such ITDs by moving them into a new ehci member
cached_itd_list. ITDs resting in cached_itd_list are moved back into their
stream's free_list once scan_periodic() detects that the active frame has
elapsed.

This makes the snd_usb_us122l driver (in kernel since .28) work right
when it's hooked up through EHCI.

[ dbrownell@users.sourceforge.net: comment fixups ]
Signed-off-by: NKarsten Wiese <fzu@wemgehoertderstaat.de>
Tested-by: NPhilippe Carriere <philippe-f.carriere@wanadoo.fr>
Tested-by: NFederico Briata <federicobriata@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

A published errata for ppc440epx states, that when running Linux with
both EHCI and OHCI modules loaded, the EHCI module experiences a fatal
error when a high-speed device is connected to the USB2.0, and
functions normally if OHCI module is not loaded.

There used to be recommendation to use only hi-speed or full-speed
devices with specific conditions, when respective module was unloaded.
Later, it was observed that ohci suspend is enough to keep things
going, and it was turned into workaround, as explained below.

Quote from original descriprion:

The 440EPx USB 2.0 Host controller is an EHCI compliant controller.  In
USB 2.0 Host controllers, each EHCI controller has one or more companion
controllers, which may be OHCI or UHCI.  An USB 2.0 Host controller will
contain one or more ports.  For each port, only one of the controllers
is connected at any one time. In the 440EPx, there is only one OHCI
companion controller, and only one USB 2.0 Host port.
All ports on an USB 2.0 controller default to the companion
controller.  If you load only an ohci driver, it will have control of
the ports and any deviceplugged in will operate, although high speed
devices will be forced to operate at full speed.  When an ehci driver
is loaded, it explicitly takes control of the ports.  If there is a
device connected, and / or every time there is a new device connected,
the ehci driver determines if the device is high speed or not.  If it
is high speed, the driver retains control of the port.  If it is not,
the driver explicitly gives the companion controller control of the
port.

The is a software workaround that uses
Initial version of the software workaround was posted to
linux-usb-devel:

http://www.mail-archive.com/linux-usb-devel@lists.sourceforge.net/msg54019.html

and later available from amcc.com:
http://www.amcc.com/Embedded/Downloads/download.html?cat=1&family=15&ins=2

The patch below is generally based on the latter, but reworked to
powerpc/of_device USB drivers, and uses a few devicetree inquiries to
get rid of (some) hardcoded defines.
Signed-off-by: NVitaly Bordug <vitb@kernel.crashing.org>
Signed-off-by: NStefan Roese <sr@denx.de>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This reverts commit f0d781d5.

It was the wrong thing to do, and does not really do what it said
it did.

Cc: Yi Yang <yi.y.yang@intel.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1147) fixes the remote-wakeup support for EHCI
controllers using the ARC/TDI "embedded-TT" core.  These controllers
turn off the RESUME bit by themselves when a port resume is complete;
hence we need to keep separate track of which ports are suspended or
in the process of resuming.

The patch also makes a couple of small improvements in ehci_irq(),
replacing reads of the command register with the value already stored
in a local variable.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Tested-by: NThomas Reitmayr <treitmayr@devbase.at>
CC: David Brownell <david-b@pacbell.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

ehci_watchdog will wake up CPU very frequently so that CPU
stays at C3 very short, average residence time is about 50
ms on Aspire One, but we expect it should be about 1 second
or more, so this kind of periodic timer is very bad for power
saving.

We can't remove this timer because of some bad USB controller
chipset, but at least we should reduce its side effect to as
possible as low.

This patch can make CPU stay at C3 longer, average residence time
is about twice as long as original. 

Please consider to apply it, thanks
Signed-off-by: NYi Yang <yi.y.yang@intel.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Now that arch/ppc is gone we don't need CONFIG_PPC_MERGE anymore remove
the dead code associated with !CONFIG_PPC_MERGE.
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

prepare x86: usb debug port early console

move ehci struct def to linux/usrb/ehci_def.h from host/ehci.h
Signed-off-by: NYinghai Lu <yhlu.kernel@gmail.com>
Acked-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: "Arjan van de Ven" <arjan@infradead.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Greg KH" <greg@kroah.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

This patch fixes some performance bugs observed with some workloads
when unlinking EHCI queue header (QH) descriptors from the async ring
(control/bulk schedule).

The mechanism intended to defer unlinking an empty QH (so there is no
penalty in common cases where it's quickly reused) was not working as
intended.  Sometimes the unlink was scheduled:

 - too quickly ... which can be a *strong* negative effect, since
   that QH becomes unavailable for immediate re-use;

 - too slowly ... wasting DMA cycles, usually a minor issue except
   for increased bus contention and power usage;

Plus there was an extreme case of "too slowly":  a logical error in the
IAA watchdog-timer conversion meant that sometimes the unlink never
got scheduled.

The fix replaces a simple counter with a timestamp derived from the
controller's 8 KHz microframe counter, and adjusts the timer usage
for some issues associated with HZ being less than 8K.

(Based on a patch originally by Alan Stern, and good troubleshooting
from  Leonid.)
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Leonid <leonidv11@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch fixes a regression in the EHCI driver's TIMER_IO_WATCHDOG
behavior.  The patch "USB: EHCI: add separate IAA watchdog timer" changed
how that timer is handled, so that short timeouts on the remaining
timer (unfortunately, overloaded) would never be used.

This takes a more direct approach, reorganizing the code slightly to
be explicit about only the I/O watchdog role now being overridable.
It also replaces a now-obsolete comment describing older timer behavior.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Leonid <leonidv11@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1097) fixes a bug in the remote-wakeup handling in
ehci-hcd.  The driver currently does not keep track of whether the
change-suspend feature is enabled for each port; the feature is
automatically reset the first time it is read.  But recent changes to
the hub driver require that the feature be read at least twice in
order to work properly.

A bit-vector is added for storing the change-suspend feature values.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Acked-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1095) cleans up the HCD glue and several of the EHCI
bus-glue files.  The ehci->is_tdi_rh_tt flag is redundant, since it
means the same thing as the hcd->has_tt flag, so it is removed and the
other flag used in its place.

Some of the bus-glue files didn't get the relinquish_port method added
to their hc_driver structures.  Although that routine currently
doesn't do anything for controllers with an integrated TT, in the
future it might.  So the patch adds it where it is missing.

Lastly, some of the bus-glue files have erroneous entries for their
hc_driver's suspend and resume methods.  These method pointers are
specific to PCI and shouldn't be used otherwise.

(The patch also includes an invisible whitespace fix.)
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Acked-by: NDavid Brownell <dbrownell@users.sourceforge.net>

While most isochronous endpoints have short polling intervals, the
EHCI driver won't necessarily handle larger ones correctly.

This patch switches to use a "u16" to represent those periods, not
a u8, since it can always work:  the largest expressible period
is 2^15 units ... not the previous too-short limit of 128 frames
(full or low speeds) or microframes (high speed, 32 frames).

This bug is essentially theoretical, since the few ISO endpoints
I've seen which don't use one transfer per frame are high speed
ones using more than that (including high bandwidth, 24 KB/msec).
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

In the EHCI driver, itd->usecs[8] is used in periodic_usecs(), indexed by
uframe.  For an ITD's unused uframes it is 0, else it contains the same
value as itd->stream->usecs.  To check if an ITD's uframe is used, we can
instead test itd->hw_transaction[uframe]:  if used, it will be nonzero no
matter what endianess is used.

This patch replaces those two uses, eliminates itd->usecs[], and saves
eight bytes from each ITD.
Signed-off-by: NKarsten Wiese <fzu@wemgehoertderstaat.de>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

EHCI Glue driver for Intel IXP4XX EHCI USB controller
Signed-off-by: NVladimir Barinov <vbarinov@ru.mvista.com>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This adds device-tree-aware ehci-ppc-of driver.
The code is based on the ehci-ppc-soc driver by
Stefan Roese <sr@denx.de>.
Signed-off-by: NValentine Barshak <vbarshak@ru.mvista.com>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NStefan Roese <sr@denx.de>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as1028) was mostly written by David Brownell; I made only
a few changes (extra log info and a small bug fix -- which might
account for why David's version had to be reverted).  It adds a new
watchdog timer to the ehci-hcd driver to be used exclusively for
detecting lost or missing IAA notifications.

Previously a shared timer had been used, which may have led to some
problems as reported by Christian Hoffmann.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

We should not have multiple line files in sysfs, this moves the data to
debugfs instead, like the UHCI driver.
Signed-off-by: NTony Jones <tonyj@suse.de>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This reverts commit 196705c9.  It was
reported to cause a regression by Daniel Exner, and Arjan van de Ven
points out that we actually already have infrastructure in place for
setting limits on acceptable DMA latency that would be the much more
correct fix for the problem with some Broadcom EHCI controllers.

Fixed up trivial conflicts due to the changes to support big-endian host
controller descriptors in drivers/usb/host/{ehci-sched.c,ehci.h}.
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch fixes the endianness select for transfer buffers in EHCI
controllers that have Transaction Translator built in the hub.  Also I
cleaned it up to make rid of magic numbers.
Signed-off-by: NVladimir Barinov <vbarinov@ru.mvista.com>
Cc: <david-b@pacbell.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch (as887) changes the way ehci-hcd and ohci-hcd handle a loss
of VBUS power during suspend.  In order for the USB-persist facility
to work correctly, it is necessary for low- and full-speed devices
attached to a high-speed port to be handed back to the companion
controller during resume processing.

This entails three changes: adding code to ehci-hcd to perform the
handover, removing code from ohci-hcd to turn off ports during
root-hub reinit, and adding code to ohci-hcd to turn on ports during
PCI controller resume.  (Other bus glue resume methods for platforms
supporting high-speed controllers would need a similar change, if any
existed.)
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Remove atomic operations on the reference counter for EHCI queue heads.
On various platforms (including ppc7448), atomic operations are unusable
with dma-coherent memory.
Signed-off-by: NSteven J. Hill <sjhill1@rockwellcollins.com>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch implements supports for EHCI controllers whose in-memory
data structures are represented in big-endian format. This is needed
(unfortunately) for the AMCC PPC440EPx SoC EHCI controller; the EHCI
spec doesn't specify little-endian format, although that's what most
other implementations use.

The guts of the patch are to introduce the hc32 type and change all
references from le32 to hc32.  All access routines are converted from
cpu_to_le32(...) to cpu_to_hc32(ehci, ...) and similar for the other
"direction".  (This is the same approach used with OHCI.)

David fixed:
	Whitespace fixes; refresh against ehci cpufreq patch; move glue
	for that PPC driver to the patch adding it; fix free symbol
	capture bugs in modified "constant" macros; and make "hc32" etc
	be "le32" unless we really need the BE options, so "sparse" can
	do some real good.
Signed-off-by: NStefan Roese <sr@denx.de>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

EHCI controllers that don't cache enough microframes can get MMF errors
when CPU frequency changes occur between the start and completion of
split interrupt transactions, due to delays in reading main memory
(caused by CPU cache snoop delays).

This patch adds a cpufreq notifier to the EHCI driver that will
inactivate split interrupt transactions during frequency transitions.
It was tested on Intel ICH7 and Serverworks/Broadcom HT1000 EHCI
controllers.
Signed-off-by: NStuart Hayes <stuart_hayes@dell.com>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

readl() et.al. expect iomem pointer, so WTF force-cast it to normal one???
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch (as710) adds a sysfs class-device attribute file named
"companion" for EHCI controllers.  The file contains a list of port
numbers that are dedicated to the companion controller; by writing a
port number to the file the user can force a high-speed device
attached directly to the computer to run at full speed.  (As far as I
know it is not possible to do this for a device attached to an
external hub.)  A port is removed from the file by writing the
negative of its port number.

Several users have asked for this facility and it seems like a useful
thing to have.  Every now and then one runs across a device which
behaves much better at full speed than at high speed.
Signed-off-by: NAlan Stern <stern@rowland.harvard.edu>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>