Maintain a per-CPU global "struct pt_regs *" variable which can be used instead
of passing regs around manually through all ~1800 interrupt handlers in the
Linux kernel.
The regs pointer is used in few places, but it potentially costs both stack
space and code to pass it around. On the FRV arch, removing the regs parameter
from all the genirq function results in a 20% speed up of the IRQ exit path
(ie: from leaving timer_interrupt() to leaving do_IRQ()).
Where appropriate, an arch may override the generic storage facility and do
something different with the variable. On FRV, for instance, the address is
maintained in GR28 at all times inside the kernel as part of general exception
handling.
Having looked over the code, it appears that the parameter may be handed down
through up to twenty or so layers of functions. Consider a USB character
device attached to a USB hub, attached to a USB controller that posts its
interrupts through a cascaded auxiliary interrupt controller. A character
device driver may want to pass regs to the sysrq handler through the input
layer which adds another few layers of parameter passing.
I've build this code with allyesconfig for x86_64 and i386. I've runtested the
main part of the code on FRV and i386, though I can't test most of the drivers.
I've also done partial conversion for powerpc and MIPS - these at least compile
with minimal configurations.
This will affect all archs. Mostly the changes should be relatively easy.
Take do_IRQ(), store the regs pointer at the beginning, saving the old one:
struct pt_regs *old_regs = set_irq_regs(regs);
And put the old one back at the end:
set_irq_regs(old_regs);
Don't pass regs through to generic_handle_irq() or __do_IRQ().
In timer_interrupt(), this sort of change will be necessary:
- update_process_times(user_mode(regs));
- profile_tick(CPU_PROFILING, regs);
+ update_process_times(user_mode(get_irq_regs()));
+ profile_tick(CPU_PROFILING);
I'd like to move update_process_times()'s use of get_irq_regs() into itself,
except that i386, alone of the archs, uses something other than user_mode().
Some notes on the interrupt handling in the drivers:
(*) input_dev() is now gone entirely. The regs pointer is no longer stored in
the input_dev struct.
(*) finish_unlinks() in drivers/usb/host/ohci-q.c needs checking. It does
something different depending on whether it's been supplied with a regs
pointer or not.
(*) Various IRQ handler function pointers have been moved to type
irq_handler_t.
Signed-Off-By: David Howells <dhowells@redhat.com>
(cherry picked from 1b16e7ac850969f38b375e511e3fa2f474a33867 commit)
Add support for older fiber versions of the SysKonnect board. These chipsets
use an internal PHY so they require special handling. The older sk98lin
driver already supported these
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
* 'upstream-linus' of master.kernel.org:/pub/scm/linux/kernel/git/jgarzik/netdev-2.6: (217 commits)
net/ieee80211: fix more crypto-related build breakage
[PATCH] Spidernet: add ethtool -S (show statistics)
[NET] GT96100: Delete bitrotting ethernet driver
[PATCH] mv643xx_eth: restrict to 32-bit PPC_MULTIPLATFORM
[PATCH] Cirrus Logic ep93xx ethernet driver
r8169: the MMIO region of the 8167 stands behin BAR#1
e1000, ixgb: Remove pointless wrappers
[PATCH] Remove powerpc specific parts of 3c509 driver
[PATCH] s2io: Switch to pci_get_device
[PATCH] gt96100: move to pci_get_device API
[PATCH] ehea: bugfix for register access functions
[PATCH] e1000 disable device on PCI error
drivers/net/phy/fixed: #if 0 some incomplete code
drivers/net: const-ify ethtool_ops declarations
[PATCH] ethtool: allow const ethtool_ops
[PATCH] sky2: big endian
[PATCH] sky2: fiber support
[PATCH] sky2: tx pause bug fix
drivers/net: Trim trailing whitespace
[PATCH] ehea: IBM eHEA Ethernet Device Driver
...
Manually resolved conflicts in drivers/net/ixgb/ixgb_main.c and
drivers/net/sky2.c related to CHECKSUM_HW/CHECKSUM_PARTIAL changes by
commit 84fa7933a3 that just happened to be
next to unrelated changes in this update.
Replace CHECKSUM_HW by CHECKSUM_PARTIAL (for outgoing packets, whose
checksum still needs to be completed) and CHECKSUM_COMPLETE (for
incoming packets, device supplied full checksum).
Patch originally from Herbert Xu, updated by myself for 2.6.18-rc3.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Because of the NAPI and other SMP fixes, let's call
this a version.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The skge driver has much better performance if transmit done is handled in
NAPI softirq. Change from doing transmit locking in driver (LLTX) and
use device lock.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The driver needs to access the IRQ status inside of lock to avoid
races with other places changing IRQ mask etc. This may be related
to some of the SMP bugs reported against skge in kernel bugzilla.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Change to use new netdev_alloc_skb interface for 2.6.18.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The user level irq balance daemon uses "eth" as a way to distinquish
ethernet devices. Also, by using device name it is possible to distinquish
different boards.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
To avoid problems with buggy protocols that assume extra header space,
use dev_alloc_skb() when allocating receive buffers.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
At the end of a critical section, we need to force the PCI write
to complete by doing a read.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The code for suspend/resume needs several fixes. The hardware lock
should be setup in probe only, not in resume. Interrupts should be
disabled during suspend, etc.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
From: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@axis.com>
Cc: Stephen Hemminger <shemminger@osdl.org>
Cc: Jeff Garzik <jeff@garzik.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Okay, Fix both typo's in one patch .The impact is that the incorrect value
was being computed for blinking LED and interrupt moderation values.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
This is needed if we wish to change the size of the resource structures.
Based on an original patch from Vivek Goyal <vgoyal@in.ibm.com>
Cc: Vivek Goyal <vgoyal@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
First of all it is unnecessary to allocate a new skb in skb_pad since
the existing one is not shared. More importantly, our hard_start_xmit
interface does not allow a new skb to be allocated since that breaks
requeueing.
This patch uses pskb_expand_head to expand the existing skb and linearize
it if needed. Actually, someone should sift through every instance of
skb_pad on a non-linear skb as they do not fit the reasons why this was
originally created.
Incidentally, this fixes a minor bug when the skb is cloned (tcpdump,
TCP, etc.). As it is skb_pad will simply write over a cloned skb. Because
of the position of the write it is unlikely to cause problems but still
it's best if we don't do it.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Sometimes boards don't reset properly, and the address read out of the
EEPROM is zero. Stop the insanity before the device gets registered.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The transmit side code has a number of ring problems that caused some
of the Bugzilla reports. Rather than trying to fix the details, it is safer
to rewrite the code that handles transmit completion and freeing.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Consolidate all usage of ring low water mark to one value.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Since accessing the PHY can take 100's of usecs, use a work queue to
allow spinning in outside of soft/hard irq.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The driver will get stuck (permanent transmit timeout), if the transmit
ring size is set too small. It needs to have enough ring elements to
hold one maximum size transmit.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Skge driver always causes bad checksums on big-endian.
The checksum in the receive control block was being swapped
when it doesn't need to be.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The Dlink DGE-560T uses Yukon2 chipset so it needs sky2 driver; and
the DGE-530T uses Yukon1 so it uses skge driver.
Bug: http://bugzilla.kernel.org/show_bug.cgi?id=6544
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
This patch fixes the problem of some Dlink cards picking the wrong
driver. It looks like these cards use Yukon 1 chipset, not Yukon 2.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Don't need to keep track of available buffers, it is simpler
to just compute the value (ala e1000). Don't need tes on link up
because should always have available buffers then.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Don't free transmit buffers until the whole set of transmit descriptors
has been marked as done. Otherwise, we risk freeing a skb before the
whole transmit is done.
This changes the transmit completion handling from incremental to a
two pass algorithm. First pass scans and records the start of the last
done descriptor, second cleans up until that point.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
In the error case we call skge_rx_reuse twice. This is harmless
but unnecessary.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The skge driver was using dev_alloc_skb which reserves space for the
Ethernet header. This unnecessary and it should just use alloc_skb,
also by using GFP_KERNEL during startup it won't run into problems when
a user asks for a huge ring size or mtu and potentially drains the
reserved atomic pool.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The skge driver aligns the header on the initial receive buffers, but
but doesn't on followon receive buffer allocations.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Reformat some code to make it easier to read. And whitespace
fixes.
Signed-off-by: Stephen Hemminger <sheminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Add mmio barriers at the appropriate places, don't have a platform
that needs them, but this is where the documentation of the patch
says to add them.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Cleanup of the part of the code that sets up DMA configuration.
Should cause no real change in operation, just clearer.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
The SysKonnect Genesis and Yukon chip sets have restrictions on the possible
control block area. The memory needs to not cross 4 Gig boundary, and it needs
to be 8 byte aligned. This patch checks and fails to bring the device up
if region is unacceptable.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Improve performance of skge driver by not touching irq mask
register as much. Since the interrupt source auto-masks, the driver
can just leave it disabled until the end of the soft irq.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Cleanup transmit buffers using NAPI. This allows the transmit routine
to leave interrupts enabled, and that improves performance.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
There is a race between updating the irq mask and setting it
which can be triggered on SMP with a bad cable.
Similar patch from Ingo Molnar and Thomas Gleixner
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
The SysKonnect Genesis based board would fail on initialization
with phy_read errors caused by not waiting for last phy write.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Fix a race in the receive NAPI, irq handling. The interrupt clear and the
start need to be separated. Otherwise there is a window between the last
frame received and the NAPI done level handling.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
This is a clone of John Linville's fixed for speed setting on sky2 driver.
The skge driver has the same code (and bug). It would not allow manually forcing
100 and 10 mbit.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
There are a couple of problems in the DMA setup code for skge.
* In the 64 bit case, it doesn't set the consistent mask.
* In the 32 bit case, the error check is backwards!
It likely will only be visible as a bug on 64 bit platforms.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
To help in reducing the number of include dependencies, several files were
touched as they were getting needed headers indirectly for stuff they use.
Thanks also to Alan Menegotto for pointing out that net/dccp/proto.c had
linux/dccp.h include twice.
Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Also have to handle out of memory condition on resume.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
If changing ring parameters is unable to allocate memory, we need
to return an error and take the device down.
Fixes-bug: http://bugzilla.kernel.org/show_bug.cgi?id=5715
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Changing the MTU size causes the receiver to have to reallocate buffers.
If this allocation fails, then we need to return an error, and take
the device offline. It can then be brought back up or reconfigured
for a smaller MTU.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Change the pause settings doesn't need to cause link to go down/up.
It can be handled by the phy_reset code.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Change the speed settings doesn't need to cause link to go down/up.
It can be handled by doing the same logic as nway_reset.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Get rid of warning in case of race with ring full and lockless
tx on the skge driver. It is possible to be in the transmit
routine with no available slots and already stopped.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
If using UDP over VLAN, with the skge driver there is a possibility
of generating an incorrect checksum. This is a unlikely occurrence
because it is only an issue on Yukon revision 0, and that revision
doesn't seem to exist on any current hardware (probably early prototype).
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Increase the driver version number and print version when
probing.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Use prefetch() in the interrupt path to try and look ahead
at the next place will be looking at in the ring.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
When skge is booted up, the PHY may be stuck in power down state
by the previous OS. So we may need to turn it on.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Skge driver was bringing link up/down when changing mac
address. This doesn't work in the bonding environment, and is
more effort than needed.
Fixes-bug: http://bugzilla.kernel.org/show_bug.cgi?id=5271
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
This is one of those workarounds sucked over from sk98lin driver.
The skge driver needs to detect the Yukon-Lite A0 chip properly,
and turn of Rx FIFO Flush.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Cleanup receive buffer allocation and management,
Add more error handling checks from PHY and bump version.
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Expand the returned data for ethtool debug access to include
all of the mapped PCI area; except for the small set of registers
that are for diagnostic RAM access. Access to those registers
will hang the system.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Merge of four previous patches and the Kconfig fix
* Remove debug printk's
* whitespace cleanup and version number change
* clear interrupts, reset phy, and reset hardware on shutdown
* ignore 64bit counter overflow interrupts
* fix a couple of places where second port could clobber state
of first port.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Both revisions share the same PCI device ID and vendor ID but revision 2
of the device uses SysKonnect's chipset whereas revision 3 of the device
uses Realtek's 8169 chipset.
Credit goes to Christiaan Lutzer <mythtv.lutzer@gmail.com> for reporting
the issue and giving the actual value for the different revisions.
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
The flush threshold in the MAC chip should be increased.
Found while reviewing vendor version of sk98lin driver.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Some versions of the Marvell yukon generate bogus sensor warning interrupts.
The driver would flood log with these messages. Handle this situation
cleanly by masking away at boot time.
Fixes: http://bugs.gentoo.org/show_bug.cgi?id=87182
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
drivers/net/skge.c | 24 ++++++++++--------------
drivers/net/skge.h | 8 ++++++--
2 files changed, 16 insertions(+), 16 deletions(-)
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Cleanup code that is used to toggle LED's. Since we
get called from ethtool, can use that thread rather than
setting up a timer.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
During autonegotiation set PHY interrupt mask to ignore
bogus speed change interrupts.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
The code to clear fifo errors was incorrect and sending garbage
to the external phy. Removed the no longer used inline's funcs.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
The check for Yukon lite changes was restricting itself to
rev A3. It turns out that these changes are also true on A4
and later.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Cleanup the phy_lock deadlock because of relocking in the nway_reset path.
Reported by Francois Romieu.
Also, don't need to do irqsave/restore for blink,
just excluding bh is good enough.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Here is a fix for a typo, thanks Eliot Dresselhaus.
Since transmitter not active when device is down, it wasn't really noticed.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
The SK-9E boards use the Marvell Yukon2 chipset which
is not supported by the skge driver. Thanks to Ralph Roesler
for noticing.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Using Genesis board, I get harmless error reports. Rather than console
error, turn it into a error counter.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>
Few more u32 vs. pm_message_t fixes.
Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Need to handle receive and transmit packet arbiter timeouts.
Transmit arbiter timeouts happens when Gigabit sends to 100Mbit port
on same switch and pause occurs.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Cleanup messages (for debug) about PHY interrrupts, because when
user can't get driver working that is often the problem.
Use a consistent way of enabling interrupts by port.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Rewrite the code for handling the Broadcom PHY to something that
works. Remove link polling because Broadcom and Yukon don't need it.
When I wrote initial code, didn't have a genesis chipset based
board to test, so it was a non-working guess.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Remove support for the non-Broadcom genesis based boards. The code
is untested, and probably won't work as is. The newer boards are all
Yukon based, and only old Genesis board I can find uses Broadcom.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Remove the bits and pieces added relating to Yukon II chipset.
The Yukon 2 will be in a separate driver.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Replace inline accessor functions for chip revision and number of ports
with simple structure members.
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
The inlines and macro's needed some cleanup's and fixes:
* change name of macro SKGEMAC_REG to SK_REG to better reflect usage
and fix comments
* ditto for SK_GEXM_REG -> SK_XMAC_REG and SKGEGMA_REG -> SK_GMA_REG
* change skge_gm_ to just gm_ since it is just a local function and long
names look ugly.
* change skge_xm_ to just xm_
* fix xm_write32 to write as two u16's with correct byte order
* fix xm_outaddr to correctly use offset
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>