linux-stable.git/drivers/usb/host, branch linux-2.6.32.y Linux kernel stable tree xhci: fix off by one error in TRB DMA address boundary check 2015-12-05T23:49:04+00:00 Mathias Nyman mathias.nyman@linux.intel.com 2015-08-03T13:07:48+00:00 70397cf66e8d1ac9b06726f5825d03342996763d commit 7895086afde2a05fa24a0e410d8e6b75ca7c8fdd upstream. We need to check that a TRB is part of the current segment before calculating its DMA address. Previously a ring segment didn't use a full memory page, and every new ring segment got a new memory page, so the off by one error in checking the upper bound was never seen. Now that we use a full memory page, 256 TRBs (4096 bytes), the off by one didn't catch the case when a TRB was the first element of the next segment. This is triggered if the virtual memory pages for a ring segment are next to each in increasing order where the ring buffer wraps around and causes errors like: [ 106.398223] xhci_hcd 0000:00:14.0: ERROR Transfer event TRB DMA ptr not part of current TD ep_index 0 comp_code 1 [ 106.398230] xhci_hcd 0000:00:14.0: Looking for event-dma fffd3000 trb-start fffd4fd0 trb-end fffd5000 seg-start fffd4000 seg-end fffd4ff0 The trb-end address is one outside the end-seg address. Tested-by: Arkadiusz Miśkiewicz <arekm@maven.pl> Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Ben Hutchings <ben@decadent.org.uk> (cherry picked from commit 6e3ae6256145b5597bee0296eb5fc384cd86aa3d) Signed-off-by: Willy Tarreau <w@1wt.eu> 
commit 7895086afde2a05fa24a0e410d8e6b75ca7c8fdd upstream.

We need to check that a TRB is part of the current segment
before calculating its DMA address.

Previously a ring segment didn't use a full memory page, and every
new ring segment got a new memory page, so the off by one
error in checking the upper bound was never seen.

Now that we use a full memory page, 256 TRBs (4096 bytes), the off by one
didn't catch the case when a TRB was the first element of the next segment.

This is triggered if the virtual memory pages for a ring segment are
next to each in increasing order where the ring buffer wraps around and
causes errors like:

[  106.398223] xhci_hcd 0000:00:14.0: ERROR Transfer event TRB DMA ptr not part of current TD ep_index 0 comp_code 1
[  106.398230] xhci_hcd 0000:00:14.0: Looking for event-dma fffd3000 trb-start fffd4fd0 trb-end fffd5000 seg-start fffd4000 seg-end fffd4ff0

The trb-end address is one outside the end-seg address.

Tested-by: Arkadiusz Miśkiewicz <arekm@maven.pl>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
(cherry picked from commit 6e3ae6256145b5597bee0296eb5fc384cd86aa3d)
Signed-off-by: Willy Tarreau <w@1wt.eu>
USB: EHCI: go back to using the system clock for QH unlinks 2013-06-10T09:43:01+00:00 Alan Stern stern@rowland.harvard.edu 2011-07-05T16:34:05+00:00 4b4963a9e7bbd37dcbdc282eecf8ba131828c450 commit 004c19682884d4f40000ce1ded53f4a1d0b18206 upstream This patch (as1477) fixes a problem affecting a few types of EHCI controller. Contrary to what one might expect, these controllers automatically stop their internal frame counter when no ports are enabled. Since ehci-hcd currently relies on the frame counter for determining when it should unlink QHs from the async schedule, those controllers run into trouble: The frame counter stops and the QHs never get unlinked. Some systems have also experienced other problems traced back to commit b963801164618e25fbdc0cd452ce49c3628b46c8 (USB: ehci-hcd unlink speedups), which made the original switch from using the system clock to using the frame counter. It never became clear what the reason was for these problems, but evidently it is related to use of the frame counter. To fix all these problems, this patch more or less reverts that commit and goes back to using the system clock. But this can't be done cleanly because other changes have since been made to the scan_async() subroutine. One of these changes involved the tricky logic that tries to avoid rescanning QHs that have already been seen when the scanning loop is restarted, which happens whenever an URB is given back. Switching back to clock-based unlinks would make this logic even more complicated. Therefore the new code doesn't rescan the entire async list whenever a giveback occurs. Instead it rescans only the current QH and continues on from there. This requires the use of a separate pointer to keep track of the next QH to scan, since the current QH may be unlinked while the scanning is in progress. That new pointer must be global, so that it can be adjusted forward whenever the _next_ QH gets unlinked. (uhci-hcd uses this same trick.) Simplification of the scanning loop removes a level of indentation, which accounts for the size of the patch. The amount of code changed is relatively small, and it isn't exactly a reversion of the b963801164 commit. This fixes Bugzilla #32432. Signed-off-by: Alan Stern <stern@rowland.harvard.edu> CC: <stable@kernel.org> Tested-by: Matej Kenda <matejken@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> Signed-off-by: Thomas Bork <tom@eisfair.net> Signed-off-by: Willy Tarreau <w@1wt.eu> 
commit 004c19682884d4f40000ce1ded53f4a1d0b18206 upstream

This patch (as1477) fixes a problem affecting a few types of EHCI
controller.  Contrary to what one might expect, these controllers
automatically stop their internal frame counter when no ports are
enabled.  Since ehci-hcd currently relies on the frame counter for
determining when it should unlink QHs from the async schedule, those
controllers run into trouble: The frame counter stops and the QHs
never get unlinked.

Some systems have also experienced other problems traced back to
commit b963801164618e25fbdc0cd452ce49c3628b46c8 (USB: ehci-hcd unlink
speedups), which made the original switch from using the system clock
to using the frame counter.  It never became clear what the reason was
for these problems, but evidently it is related to use of the frame
counter.

To fix all these problems, this patch more or less reverts that commit
and goes back to using the system clock.  But this can't be done
cleanly because other changes have since been made to the scan_async()
subroutine.  One of these changes involved the tricky logic that tries
to avoid rescanning QHs that have already been seen when the scanning
loop is restarted, which happens whenever an URB is given back.
Switching back to clock-based unlinks would make this logic even more
complicated.

Therefore the new code doesn't rescan the entire async list whenever a
giveback occurs.  Instead it rescans only the current QH and continues
on from there.  This requires the use of a separate pointer to keep
track of the next QH to scan, since the current QH may be unlinked
while the scanning is in progress.  That new pointer must be global,
so that it can be adjusted forward whenever the _next_ QH gets
unlinked.  (uhci-hcd uses this same trick.)

Simplification of the scanning loop removes a level of indentation,
which accounts for the size of the patch.  The amount of code changed
is relatively small, and it isn't exactly a reversion of the
b963801164 commit.

This fixes Bugzilla #32432.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
CC: <stable@kernel.org>
Tested-by: Matej Kenda <matejken@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Thomas Bork <tom@eisfair.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
xhci: Make handover code more robust 2013-06-10T09:43:01+00:00 Matthew Garrett mjg@redhat.com 2012-08-14T20:44:49+00:00 1238778a3ee1ff35da4d47dac157f03c557d2d86 commit e955a1cd086de4d165ae0f4c7be7289d84b63bdc upstream. My test platform (Intel DX79SI) boots reliably under BIOS, but frequently crashes when booting via UEFI. I finally tracked this down to the xhci handoff code. It seems that reads from the device occasionally just return 0xff, resulting in xhci_find_next_cap_offset generating a value that's larger than the resource region. We then oops when attempting to read the value. Sanity checking that value lets us avoid the crash. I've no idea what's causing the underlying problem, and xhci still doesn't actually *work* even with this, but the machine at least boots which will probably make further debugging easier. This should be backported to kernels as old as 2.6.31, that contain the commit 66d4eadd8d067269ea8fead1a50fe87c2979a80d "USB: xhci: BIOS handoff and HW initialization." Signed-off-by: Matthew Garrett <mjg@redhat.com> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> 
commit e955a1cd086de4d165ae0f4c7be7289d84b63bdc upstream.

My test platform (Intel DX79SI) boots reliably under BIOS, but frequently
crashes when booting via UEFI. I finally tracked this down to the xhci
handoff code. It seems that reads from the device occasionally just return
0xff, resulting in xhci_find_next_cap_offset generating a value that's
larger than the resource region. We then oops when attempting to read the
value. Sanity checking that value lets us avoid the crash.

I've no idea what's causing the underlying problem, and xhci still doesn't
actually *work* even with this, but the machine at least boots which will
probably make further debugging easier.

This should be backported to kernels as old as 2.6.31, that contain the
commit 66d4eadd8d067269ea8fead1a50fe87c2979a80d "USB: xhci: BIOS handoff
and HW initialization."

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
xhci: Increase reset timeout for Renesas 720201 host. 2012-10-07T21:38:18+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2012-07-23T23:06:08+00:00 5b61f615f559fe37b4e0a5d4cb2942b231c7dcc8 commit 22ceac191211cf6688b1bf6ecd93c8b6bf80ed9b upstream. The NEC/Renesas 720201 xHCI host controller does not complete its reset within 250 milliseconds. In fact, it takes about 9 seconds to reset the host controller, and 1 second for the host to be ready for doorbell rings. Extend the reset and CNR polling timeout to 10 seconds each. This patch should be backported to kernels as old as 2.6.31, that contain the commit 66d4eadd8d067269ea8fead1a50fe87c2979a80d "USB: xhci: BIOS handoff and HW initialization." Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Reported-by: Edwin Klein Mentink <e.kleinmentink@zonnet.nl> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> 
commit 22ceac191211cf6688b1bf6ecd93c8b6bf80ed9b upstream.

The NEC/Renesas 720201 xHCI host controller does not complete its reset
within 250 milliseconds.  In fact, it takes about 9 seconds to reset the
host controller, and 1 second for the host to be ready for doorbell
rings.  Extend the reset and CNR polling timeout to 10 seconds each.

This patch should be backported to kernels as old as 2.6.31, that
contain the commit 66d4eadd8d067269ea8fead1a50fe87c2979a80d "USB: xhci:
BIOS handoff and HW initialization."

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-by: Edwin Klein Mentink <e.kleinmentink@zonnet.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
xhci: Reset reserved command ring TRBs on cleanup. 2012-10-07T21:37:52+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2012-05-08T14:09:26+00:00 6dd99cb6c03ddf85b4d30b7c8432c76644312a89 commit 33b2831ac870d50cc8e01c317b07fb1e69c13fe1 upstream. When the xHCI driver needs to clean up memory (perhaps due to a failed register restore on resume from S3 or resume from S4), it needs to reset the number of reserved TRBs on the command ring to zero. Otherwise, several resume cycles (about 30) with a UAS device attached will continually increment the number of reserved TRBs, until all command submissions fail because there isn't enough room on the command ring. This patch should be backported to kernels as old as 2.6.32, that contain the commit 913a8a344ffcaf0b4a586d6662a2c66a7106557d "USB: xhci: Change how xHCI commands are handled." Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> 
commit 33b2831ac870d50cc8e01c317b07fb1e69c13fe1 upstream.

When the xHCI driver needs to clean up memory (perhaps due to a failed
register restore on resume from S3 or resume from S4), it needs to reset
the number of reserved TRBs on the command ring to zero.  Otherwise,
several resume cycles (about 30) with a UAS device attached will
continually increment the number of reserved TRBs, until all command
submissions fail because there isn't enough room on the command ring.

This patch should be backported to kernels as old as 2.6.32,
that contain the commit 913a8a344ffcaf0b4a586d6662a2c66a7106557d
"USB: xhci: Change how xHCI commands are handled."

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
xHCI: Correct the #define XHCI_LEGACY_DISABLE_SMI 2012-10-07T21:37:42+00:00 Alex He alex.he@amd.com 2012-03-30T02:21:38+00:00 79c23081de12a2d61529174f153400b7586c2cf9 commit 95018a53f7653e791bba1f54c8d75d9cb700d1bd upstream. Re-define XHCI_LEGACY_DISABLE_SMI and used it in right way. All SMI enable bits will be cleared to zero and flag bits 29:31 are also cleared to zero. Other bits should be presvered as Table 146. This patch should be backported to kernels as old as 2.6.31. Signed-off-by: Alex He <alex.he@amd.com> Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> 
commit 95018a53f7653e791bba1f54c8d75d9cb700d1bd upstream.

Re-define XHCI_LEGACY_DISABLE_SMI and used it in right way. All SMI enable
bits will be cleared to zero and flag bits 29:31 are also cleared to zero.
Other bits should be presvered as Table 146.

This patch should be backported to kernels as old as 2.6.31.

Signed-off-by: Alex He <alex.he@amd.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
xhci: Don't write zeroed pointers to xHC registers. 2012-10-07T21:37:41+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2012-03-16T20:09:39+00:00 737b15bb831a1ada007772b4165a3c5c0562787f commit 159e1fcc9a60fc7daba23ee8fcdb99799de3fe84 upstream. When xhci_mem_cleanup() is called, we can't be sure if the xHC is actually halted. We can ask the xHC to halt by writing to the RUN bit in the command register, but that might timeout due to a HW hang. If the host controller is still running, we should not write zeroed values to the event ring dequeue pointers or base tables, the DCBAA pointers, or the command ring pointers. Eric Fu reports his VIA VL800 host accesses the event ring pointers after a failed register restore on resume from suspend. The hypothesis is that the host never actually halted before the register write to change the event ring pointer to zero. Remove all writes of zeroed values to pointer registers in xhci_mem_cleanup(). Instead, make all callers of the function reset the host controller first, which will reset those registers to zero. xhci_mem_init() is the only caller that doesn't first halt and reset the host controller before calling xhci_mem_cleanup(). This should be backported to kernels as old as 2.6.32. Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Tested-by: Elric Fu <elricfu1@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Willy Tarreau <w@1wt.eu> 
commit 159e1fcc9a60fc7daba23ee8fcdb99799de3fe84 upstream.

When xhci_mem_cleanup() is called, we can't be sure if the xHC is
actually halted.  We can ask the xHC to halt by writing to the RUN bit
in the command register, but that might timeout due to a HW hang.

If the host controller is still running, we should not write zeroed
values to the event ring dequeue pointers or base tables, the DCBAA
pointers, or the command ring pointers.  Eric Fu reports his VIA VL800
host accesses the event ring pointers after a failed register restore on
resume from suspend.  The hypothesis is that the host never actually
halted before the register write to change the event ring pointer to
zero.

Remove all writes of zeroed values to pointer registers in
xhci_mem_cleanup().  Instead, make all callers of the function reset the
host controller first, which will reset those registers to zero.
xhci_mem_init() is the only caller that doesn't first halt and reset the
host controller before calling xhci_mem_cleanup().

This should be backported to kernels as old as 2.6.32.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Tested-by: Elric Fu <elricfu1@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
xhci: Fix encoding for HS bulk/control NAK rate. 2012-03-04T17:49:21+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2012-02-13T22:42:11+00:00 5027714da2c8288d7ea39309bf66020a2e14a5d5 commit 340a3504fd39dad753ba908fb6f894ee81fc3ae2 upstream. The xHCI 0.96 spec says that HS bulk and control endpoint NAK rate must be encoded as an exponent of two number of microframes. The endpoint descriptor has the NAK rate encoded in number of microframes. We were just copying the value from the endpoint descriptor into the endpoint context interval field, which was not correct. This lead to the VIA host rejecting the add of a bulk OUT endpoint from any USB 2.0 mass storage device. The fix is to use the correct encoding. Refactor the code to convert number of frames to an exponential number of microframes, and make sure we convert the number of microframes in HS bulk and control endpoints to an exponent. This should be back ported to kernels as old as 2.6.31, that contain the commit dfa49c4ad120a784ef1ff0717168aa79f55a483a "USB: xhci - fix math in xhci_get_endpoint_interval" Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Tested-by: Felipe Contreras <felipe.contreras@gmail.com> Suggested-by: Andiry Xu <andiry.xu@amd.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit 340a3504fd39dad753ba908fb6f894ee81fc3ae2 upstream.

The xHCI 0.96 spec says that HS bulk and control endpoint NAK rate must
be encoded as an exponent of two number of microframes.  The endpoint
descriptor has the NAK rate encoded in number of microframes.  We were
just copying the value from the endpoint descriptor into the endpoint
context interval field, which was not correct.  This lead to the VIA
host rejecting the add of a bulk OUT endpoint from any USB 2.0 mass
storage device.

The fix is to use the correct encoding.  Refactor the code to convert
number of frames to an exponential number of microframes, and make sure
we convert the number of microframes in HS bulk and control endpoints to
an exponent.

This should be back ported to kernels as old as 2.6.31, that contain the
commit dfa49c4ad120a784ef1ff0717168aa79f55a483a "USB: xhci - fix math
in xhci_get_endpoint_interval"

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Tested-by: Felipe Contreras <felipe.contreras@gmail.com>
Suggested-by: Andiry Xu <andiry.xu@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
USB: Fix handoff when BIOS disables host PCI device. 2012-03-04T17:49:21+00:00 Sarah Sharp sarah.a.sharp@linux.intel.com 2012-02-07T23:11:46+00:00 addf2e1999cc01c2d4c46a70aba505f9504c8719 commit cab928ee1f221c9cc48d6615070fefe2e444384a upstream. On some systems with an Intel Panther Point xHCI host controller, the BIOS disables the xHCI PCI device during boot, and switches the xHCI ports over to EHCI. This allows the BIOS to access USB devices without having xHCI support. The downside is that the xHCI BIOS handoff mechanism will fail because memory mapped I/O is not enabled for the disabled PCI device. Jesse Barnes says this is expected behavior. The PCI core will enable BARs before quirks run, but it will leave it in an undefined state, and it may not have memory mapped I/O enabled. Make the generic USB quirk handler call pci_enable_device() to re-enable MMIO, and call pci_disable_device() once the host-specific BIOS handoff is finished. This will balance the ref counts in the PCI core. When the PCI probe function is called, usb_hcd_pci_probe() will call pci_enable_device() again. This should be back ported to kernels as old as 2.6.31. That was the first kernel with xHCI support, and no one has complained about BIOS handoffs failing due to memory mapped I/O being disabled on other hosts (EHCI, UHCI, or OHCI). Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com> Acked-by: Oliver Neukum <oneukum@suse.de> Cc: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit cab928ee1f221c9cc48d6615070fefe2e444384a upstream.

On some systems with an Intel Panther Point xHCI host controller, the
BIOS disables the xHCI PCI device during boot, and switches the xHCI
ports over to EHCI.  This allows the BIOS to access USB devices without
having xHCI support.

The downside is that the xHCI BIOS handoff mechanism will fail because
memory mapped I/O is not enabled for the disabled PCI device.
Jesse Barnes says this is expected behavior.  The PCI core will enable
BARs before quirks run, but it will leave it in an undefined state, and
it may not have memory mapped I/O enabled.

Make the generic USB quirk handler call pci_enable_device() to re-enable
MMIO, and call pci_disable_device() once the host-specific BIOS handoff
is finished.  This will balance the ref counts in the PCI core.  When
the PCI probe function is called, usb_hcd_pci_probe() will call
pci_enable_device() again.

This should be back ported to kernels as old as 2.6.31.  That was the
first kernel with xHCI support, and no one has complained about BIOS
handoffs failing due to memory mapped I/O being disabled on other hosts
(EHCI, UHCI, or OHCI).

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Acked-by: Oliver Neukum <oneukum@suse.de>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
usb: Skip PCI USB quirk handling for Netlogic XLP 2012-02-13T19:28:50+00:00 Jayachandran C jayachandranc@netlogicmicro.com 2012-01-27T14:57:32+00:00 6da6c702a675b75f7c4bcc23ca3befcd25bb07e4 commit e4436a7c17ac2b5e138f93f83a541cba9b311685 upstream. The Netlogic XLP SoC's on-chip USB controller appears as a PCI USB device, but does not need the EHCI/OHCI handoff done in usb/host/pci-quirks.c. The pci-quirks.c is enabled for all vendors and devices, and is enabled if USB and PCI are configured. If we do not skip the qurik handling on XLP, the readb() call in ehci_bios_handoff() will cause a crash since byte access is not supported for EHCI registers in XLP. Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com> Acked-by: Alan Stern <stern@rowland.harvard.edu> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> 
commit e4436a7c17ac2b5e138f93f83a541cba9b311685 upstream.

The Netlogic XLP SoC's on-chip USB controller appears as a PCI
USB device, but does not need the EHCI/OHCI handoff done in
usb/host/pci-quirks.c.

The pci-quirks.c is enabled for all vendors and devices, and is
enabled if USB and PCI are configured.

If we do not skip the qurik handling on XLP, the readb() call in
ehci_bios_handoff() will cause a crash since byte access is not
supported for EHCI registers in XLP.

Signed-off-by: Jayachandran C <jayachandranc@netlogicmicro.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>