Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

[Douglas Miller]

(Sorry if you got several duplicates, am trying to work through rejected 
messages due to supposed HTML content)

The following behavior is being observed when running "ethtool -t <dev> 
offline" on ports on the Broadcom BCM5719 adapter (tg3 driver). The 
ports have wrap plugs on them, although I'm not sure why that would have 
any affect.

The test "ethtool -t <dev> offline" was being running continuously. The 
first invocation passes, all subsequent ones fail (at least in the "link 
test" step) after ~20 second timeout. When running the test once, I see 
the following: Looking at /var/log/messages, I see a "Link is down" 
message during the test. Then, 20 seconds after the test completes, 
there is a "Link is up..." message. If I wait for the "Link is up..." 
message I can run the test without problems. If the test is run again 
while the link is still down, it fails and seems to delay the "link up" 
by an additional 20 seconds.

If I run "external_lb" instead of "offline", I am able to run the test 
repeatedly without error. So it seems that some action taken in the 
"external_lb" case actually "repairs" the port. But the "external_lb" 
test also exhibits the link-down for 20 seconds symptom, although it can 
been run while the link is considered "down" without failure.

The first question is whether we should expect to be able to run 
"ethtool -t <dev> offline" continually, with no delay between runs. I 
presume this is supported.

Second question, I would like someone with experience with the tg3 
driver and this adapter to comment on what might be done to fix this. My 
first, simple, guess would be move the "tg3_phy_lpbk_set(tp, 0, true);" 
setting (in tg3_test_loopback()) to be done for both "offline" and 
"external_lb" cases. I am awaiting time on a system with this adapter in 
order to try out some possible fixes and/or debug what might be 
wrong/different with the configuration after the "offline" test.

I would appreciate any help,
Thanks,
Doug Miller

Re: Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

[Michael Chan]

On Tue, 2015-08-11 at 10:59 -0500, Douglas Miller wrote: 
> (Sorry if you got several duplicates, am trying to work through rejected 
> messages due to supposed HTML content)
> 
> The following behavior is being observed when running "ethtool -t <dev> 
> offline" on ports on the Broadcom BCM5719 adapter (tg3 driver). The 
> ports have wrap plugs on them, although I'm not sure why that would have 
> any affect.

I'm not sure what are wrap plugs.

> 
> The test "ethtool -t <dev> offline" was being running continuously. The 
> first invocation passes, all subsequent ones fail (at least in the "link 
> test" step) after ~20 second timeout. When running the test once, I see 
> the following: Looking at /var/log/messages, I see a "Link is down" 
> message during the test. Then, 20 seconds after the test completes, 
> there is a "Link is up..." message. If I wait for the "Link is up..." 
> message I can run the test without problems. If the test is run again 
> while the link is still down, it fails and seems to delay the "link up" 
> by an additional 20 seconds.

When you do offline test, the chip is reset and the PHY is also reset,
causing the link to go down.  Normally, link should come back up within
a few seconds.  The selftest code will wait for 6 seconds for copper and
2 seconds for serdes link to be up before declaring there is no link.

So for whaever reason, the link in your setup takes longer than that to
come up and therefore it fails the link test when you run it in a loop
starting on the 2nd iteration.


> If I run "external_lb" instead of "offline", I am able to run the test 
> repeatedly without error. So it seems that some action taken in the 
> "external_lb" case actually "repairs" the port. But the "external_lb" 
> test also exhibits the link-down for 20 seconds symptom, although it can 
> been run while the link is considered "down" without failure.

External loopback requires a loopback cable.  So you must have a
loopback cable for this test to pass.  May be that's what you meant by
wrap plugs.

> 
> The first question is whether we should expect to be able to run 
> "ethtool -t <dev> offline" continually, with no delay between runs. I 
> presume this is supported.

If your intention is to run external loopback, yes you should specify
external loopback.  Otherwise the driver expects normal link behavior
and that's why it fails.

If you connect a normal cable, then ethtool -t <dev> offline works
repeatedly, right?

> 
> Second question, I would like someone with experience with the tg3 
> driver and this adapter to comment on what might be done to fix this. My 
> first, simple, guess would be move the "tg3_phy_lpbk_set(tp, 0, true);" 
> setting (in tg3_test_loopback()) to be done for both "offline" and 
> "external_lb" cases. I am awaiting time on a system with this adapter in 
> order to try out some possible fixes and/or debug what might be 
> wrong/different with the configuration after the "offline" test.
> 
> I would appreciate any help,
> Thanks,
> Doug Miller
> 

Re: Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

[Douglas Miller]

Thanks Michael for getting back to me.

Yes, the "wrap plugs" are the loopback cables/plugs. It is my 
understanding that the "offline" tests do not require anything to be 
plugged into the ports, as they do not in any way touch the "external" 
port. They perform an "internal loopback" test which does not depend on 
any external connection.

 From what I can tell, the only difference between "offline" and 
"external_lb" is that "external_lb" performs the external loopback 
tests, *in addition to* all the tests done for "offline". This would 
imply that the only tests that depend on anything connected to the 
physical port is "external_lb", and there is no requirement that the 
wrap plugs be removed/replaced in order to run "offline" tests.

In the case I was debugging, wrap plugs were installed because the ports 
were, later, being tested in an "external loopback" way.

What I am observing is that it takes about 20 seconds for the kernel to 
declare that the link is up, after running the "offline" or 
"external_lb" test. In the case of "offline" I cannot run the test again 
until the kernel declares the link up. In the case of "external_lb" I 
can run the test again immediately and it passes. This suggests to me 
that the "external_lb" case (again, it is a superset of "offline") is 
performing some configuration on the port that allows the subsequent 
test to work. The one significant difference between "offline" and 
"external_lb" is that "external_lb" performs the
"tg3_phy_lpbk_set(tp, 0, true);" changes to configuration (immediately 
prior to running the loopback tests again). I believe this call is to 
switch from "internal loopback" to "normal", in order to leverage the 
wrap plugs and perform the external loopback tests. But this call is not 
made for "offline" and I am wondering if that leaves the port in a state 
where it cannot be used until the kernel completes the "link up".

Thanks,
Doug



On 08/11/2015 12:41 PM, Michael Chan wrote:
> On Tue, 2015-08-11 at 10:59 -0500, Douglas Miller wrote:
>> (Sorry if you got several duplicates, am trying to work through rejected
>> messages due to supposed HTML content)
>>
>> The following behavior is being observed when running "ethtool -t <dev>
>> offline" on ports on the Broadcom BCM5719 adapter (tg3 driver). The
>> ports have wrap plugs on them, although I'm not sure why that would have
>> any affect.
> I'm not sure what are wrap plugs.
>
>> The test "ethtool -t <dev> offline" was being running continuously. The
>> first invocation passes, all subsequent ones fail (at least in the "link
>> test" step) after ~20 second timeout. When running the test once, I see
>> the following: Looking at /var/log/messages, I see a "Link is down"
>> message during the test. Then, 20 seconds after the test completes,
>> there is a "Link is up..." message. If I wait for the "Link is up..."
>> message I can run the test without problems. If the test is run again
>> while the link is still down, it fails and seems to delay the "link up"
>> by an additional 20 seconds.
> When you do offline test, the chip is reset and the PHY is also reset,
> causing the link to go down.  Normally, link should come back up within
> a few seconds.  The selftest code will wait for 6 seconds for copper and
> 2 seconds for serdes link to be up before declaring there is no link.
>
> So for whaever reason, the link in your setup takes longer than that to
> come up and therefore it fails the link test when you run it in a loop
> starting on the 2nd iteration.
>
>
>> If I run "external_lb" instead of "offline", I am able to run the test
>> repeatedly without error. So it seems that some action taken in the
>> "external_lb" case actually "repairs" the port. But the "external_lb"
>> test also exhibits the link-down for 20 seconds symptom, although it can
>> been run while the link is considered "down" without failure.
> External loopback requires a loopback cable.  So you must have a
> loopback cable for this test to pass.  May be that's what you meant by
> wrap plugs.
>
>> The first question is whether we should expect to be able to run
>> "ethtool -t <dev> offline" continually, with no delay between runs. I
>> presume this is supported.
> If your intention is to run external loopback, yes you should specify
> external loopback.  Otherwise the driver expects normal link behavior
> and that's why it fails.
>
> If you connect a normal cable, then ethtool -t <dev> offline works
> repeatedly, right?
>
>> Second question, I would like someone with experience with the tg3
>> driver and this adapter to comment on what might be done to fix this. My
>> first, simple, guess would be move the "tg3_phy_lpbk_set(tp, 0, true);"
>> setting (in tg3_test_loopback()) to be done for both "offline" and
>> "external_lb" cases. I am awaiting time on a system with this adapter in
>> order to try out some possible fixes and/or debug what might be
>> wrong/different with the configuration after the "offline" test.
>>
>> I would appreciate any help,
>> Thanks,
>> Doug Miller
>>
>

Re: Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

[Michael Chan]

On Tue, 2015-08-11 at 14:24 -0500, Douglas Miller wrote: 
> Yes, the "wrap plugs" are the loopback cables/plugs. It is my 
> understanding that the "offline" tests do not require anything to be 
> plugged into the ports, as they do not in any way touch the "external" 
> port. They perform an "internal loopback" test which does not depend on 
> any external connection.

Correct.

> 
>  From what I can tell, the only difference between "offline" and 
> "external_lb" is that "external_lb" performs the external loopback 
> tests, *in addition to* all the tests done for "offline".

Correct.

> This would 
> imply that the only tests that depend on anything connected to the 
> physical port is "external_lb", and there is no requirement that the 
> wrap plugs be removed/replaced in order to run "offline" tests.

When you do external loopback test, we skip the link test because you no
longer have normal connection to the network.  You now use a special
loopback cable, which will fail the link up test because the link up
test assumes connection to the network using normal cable.

> 
> In the case I was debugging, wrap plugs were installed because the ports 
> were, later, being tested in an "external loopback" way.
> 
> What I am observing is that it takes about 20 seconds for the kernel to 
> declare that the link is up, after running the "offline" or 
> "external_lb" test. In the case of "offline" I cannot run the test again 
> until the kernel declares the link up. In the case of "external_lb" I 
> can run the test again immediately and it passes.

As stated earlier, because we skip the link test when we are performing
external_lb.

So, you should always do ethtool -t <dev> external_lb if you have a
loopback cable connected.  We will perform the external loopback test
and skip the link test.

If you don't have an external loopback cable connected, you should run
ethtool -t <dev> offline.  It will not do the external loopback test and
will do the link test for proper link up with the network.

> This suggests to me 
> that the "external_lb" case (again, it is a superset of "offline") is 
> performing some configuration on the port that allows the subsequent 
> test to work. The one significant difference between "offline" and 
> "external_lb" is that "external_lb" performs the
> "tg3_phy_lpbk_set(tp, 0, true);" changes to configuration (immediately 
> prior to running the loopback tests again). I believe this call is to 
> switch from "internal loopback" to "normal", in order to leverage the 
> wrap plugs and perform the external loopback tests. But this call is not 
> made for "offline" and I am wondering if that leaves the port in a state 
> where it cannot be used until the kernel completes the "link up".
> 
> 

Re: Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

[Douglas Miller]

Oh, I had missed the extra "if" condition on tg3_test_link(). So 
"external_lb" is not a true superset of "offline".

So you are not surprised by the (about) 20 second "link down" period 
after this test? If this is expected (albeit undocumented) behavior we 
can change the test scenario to work around it. It seems as though not 
all adapters exhibit this same symptom. From a testing standpoint, it is 
a long delay to add that may only be needed for this one adapter 
(Broadcom BCM5719, or adapter family).

Thanks,
Doug

On 08/11/2015 03:31 PM, Michael Chan wrote:
> On Tue, 2015-08-11 at 14:24 -0500, Douglas Miller wrote:
>> Yes, the "wrap plugs" are the loopback cables/plugs. It is my
>> understanding that the "offline" tests do not require anything to be
>> plugged into the ports, as they do not in any way touch the "external"
>> port. They perform an "internal loopback" test which does not depend on
>> any external connection.
> Correct.
>
>>   From what I can tell, the only difference between "offline" and
>> "external_lb" is that "external_lb" performs the external loopback
>> tests, *in addition to* all the tests done for "offline".
> Correct.
>
>> This would
>> imply that the only tests that depend on anything connected to the
>> physical port is "external_lb", and there is no requirement that the
>> wrap plugs be removed/replaced in order to run "offline" tests.
> When you do external loopback test, we skip the link test because you no
> longer have normal connection to the network.  You now use a special
> loopback cable, which will fail the link up test because the link up
> test assumes connection to the network using normal cable.
>
>> In the case I was debugging, wrap plugs were installed because the ports
>> were, later, being tested in an "external loopback" way.
>>
>> What I am observing is that it takes about 20 seconds for the kernel to
>> declare that the link is up, after running the "offline" or
>> "external_lb" test. In the case of "offline" I cannot run the test again
>> until the kernel declares the link up. In the case of "external_lb" I
>> can run the test again immediately and it passes.
> As stated earlier, because we skip the link test when we are performing
> external_lb.
>
> So, you should always do ethtool -t <dev> external_lb if you have a
> loopback cable connected.  We will perform the external loopback test
> and skip the link test.
>
> If you don't have an external loopback cable connected, you should run
> ethtool -t <dev> offline.  It will not do the external loopback test and
> will do the link test for proper link up with the network.
>
>> This suggests to me
>> that the "external_lb" case (again, it is a superset of "offline") is
>> performing some configuration on the port that allows the subsequent
>> test to work. The one significant difference between "offline" and
>> "external_lb" is that "external_lb" performs the
>> "tg3_phy_lpbk_set(tp, 0, true);" changes to configuration (immediately
>> prior to running the loopback tests again). I believe this call is to
>> switch from "internal loopback" to "normal", in order to leverage the
>> wrap plugs and perform the external loopback tests. But this call is not
>> made for "offline" and I am wondering if that leaves the port in a state
>> where it cannot be used until the kernel completes the "link up".
>>
>>

Re: Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

[Siva Reddy (Siva) Kallam]

On 8/12/2015 6:02 PM, Douglas Miller wrote:
> Oh, I had missed the extra "if" condition on tg3_test_link(). So 
> "external_lb" is not a true superset of "offline".
>
> So you are not surprised by the (about) 20 second "link down" period 
> after this test? If this is expected (albeit undocumented) behavior we 
> can change the test scenario to work around it. It seems as though not 
> all adapters exhibit this same symptom. From a testing standpoint, it 
> is a long delay to add that may only be needed for this one adapter 
> (Broadcom BCM5719, or adapter family).
>
We executed the "ethtool -t <dev> offline" in a loop on our local test 
machine with 5719 and linkup time is <= 5 secs.

Script:
#!/bin/bash
echo "---------OS Information---------"
uname -a
echo "----------Card Information----------"
lspci | grep 5719
echo "----------Interface information------"
ethtool -i p4p4
echo "---------Offline test start----------"
for i in 1 2 3
do
     date
     ethtool -t p4p4 offline
done

Output:

---------OS Information---------
Linux siva-dev 4.2.0-rc4+ #1 SMP Thu Aug 13 20:24:11 IST 2015 x86_64 
x86_64 x86_64 GNU/Linux
----------Card Information----------
03:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
Gigabit Ethernet PCIe (rev 01)
03:00.1 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
Gigabit Ethernet PCIe (rev 01)
03:00.2 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
Gigabit Ethernet PCIe (rev 01)
03:00.3 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
Gigabit Ethernet PCIe (rev 01)
----------Interface information------
driver: tg3
version: 3.137
firmware-version: 5719-v1.41 NCSI v1.3.6.0
bus-info: 0000:03:00.3
supports-statistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
supports-priv-flags: no
---------Offline test start----------
Thu Aug 13 22:05:59 IST 2015
The test result is PASS
The test extra info:
nvram test        (online)      0
link test         (online)      0
register test     (offline)     0
memory test       (offline)     0
mac loopback test (offline)     0
phy loopback test (offline)     0
ext loopback test (offline)     0
interrupt test    (offline)     0

Thu Aug 13 22:06:00 IST 2015
The test result is PASS
The test extra info:
nvram test        (online)      0
link test         (online)      0
register test     (offline)     0
memory test       (offline)     0
mac loopback test (offline)     0
phy loopback test (offline)     0
ext loopback test (offline)     0
interrupt test    (offline)     0

Thu Aug 13 22:06:05 IST 2015
The test result is PASS
The test extra info:
nvram test        (online)      0
link test         (online)      0
register test     (offline)     0
memory test       (offline)     0
mac loopback test (offline)     0
phy loopback test (offline)     0
ext loopback test (offline)     0
interrupt test    (offline)     0

Please check your test environment.

> Thanks,
> Doug
>
> On 08/11/2015 03:31 PM, Michael Chan wrote:
>> On Tue, 2015-08-11 at 14:24 -0500, Douglas Miller wrote:
>>> Yes, the "wrap plugs" are the loopback cables/plugs. It is my
>>> understanding that the "offline" tests do not require anything to be
>>> plugged into the ports, as they do not in any way touch the "external"
>>> port. They perform an "internal loopback" test which does not depend on
>>> any external connection.
>> Correct.
>>
>>>   From what I can tell, the only difference between "offline" and
>>> "external_lb" is that "external_lb" performs the external loopback
>>> tests, *in addition to* all the tests done for "offline".
>> Correct.
>>
>>> This would
>>> imply that the only tests that depend on anything connected to the
>>> physical port is "external_lb", and there is no requirement that the
>>> wrap plugs be removed/replaced in order to run "offline" tests.
>> When you do external loopback test, we skip the link test because you no
>> longer have normal connection to the network.  You now use a special
>> loopback cable, which will fail the link up test because the link up
>> test assumes connection to the network using normal cable.
>>
>>> In the case I was debugging, wrap plugs were installed because the 
>>> ports
>>> were, later, being tested in an "external loopback" way.
>>>
>>> What I am observing is that it takes about 20 seconds for the kernel to
>>> declare that the link is up, after running the "offline" or
>>> "external_lb" test. In the case of "offline" I cannot run the test 
>>> again
>>> until the kernel declares the link up. In the case of "external_lb" I
>>> can run the test again immediately and it passes.
>> As stated earlier, because we skip the link test when we are performing
>> external_lb.
>>
>> So, you should always do ethtool -t <dev> external_lb if you have a
>> loopback cable connected.  We will perform the external loopback test
>> and skip the link test.
>>
>> If you don't have an external loopback cable connected, you should run
>> ethtool -t <dev> offline.  It will not do the external loopback test and
>> will do the link test for proper link up with the network.
>>
>>> This suggests to me
>>> that the "external_lb" case (again, it is a superset of "offline") is
>>> performing some configuration on the port that allows the subsequent
>>> test to work. The one significant difference between "offline" and
>>> "external_lb" is that "external_lb" performs the
>>> "tg3_phy_lpbk_set(tp, 0, true);" changes to configuration (immediately
>>> prior to running the loopback tests again). I believe this call is to
>>> switch from "internal loopback" to "normal", in order to leverage the
>>> wrap plugs and perform the external loopback tests. But this call is 
>>> not
>>> made for "offline" and I am wondering if that leaves the port in a 
>>> state
>>> where it cannot be used until the kernel completes the "link up".
>>>
>>>
>

Re: Question on behavior of tg3_self_test() (ethtool -t on tg3 driver)

[Douglas Miller]

Very interesting. I was running a RHEL 7.1 kernel 
3.10.0-229.ael7b.ppc64le (PowerPC). tg3 version 3.137, firmware 
5719-v1.24i,  but unknown what patches were added to either of our modules.

We will investigate the environment more, under the assumption that we 
should not be required to insert any delay between runs of ethtool -t 
... offline.

Thanks Siva,
Doug

On 08/13/2015 03:40 AM, Siva Reddy (Siva) Kallam wrote:
>
>
> On 8/12/2015 6:02 PM, Douglas Miller wrote:
>> Oh, I had missed the extra "if" condition on tg3_test_link(). So 
>> "external_lb" is not a true superset of "offline".
>>
>> So you are not surprised by the (about) 20 second "link down" period 
>> after this test? If this is expected (albeit undocumented) behavior 
>> we can change the test scenario to work around it. It seems as though 
>> not all adapters exhibit this same symptom. From a testing 
>> standpoint, it is a long delay to add that may only be needed for 
>> this one adapter (Broadcom BCM5719, or adapter family).
>>
> We executed the "ethtool -t <dev> offline" in a loop on our local test 
> machine with 5719 and linkup time is <= 5 secs.
>
> Script:
> #!/bin/bash
> echo "---------OS Information---------"
> uname -a
> echo "----------Card Information----------"
> lspci | grep 5719
> echo "----------Interface information------"
> ethtool -i p4p4
> echo "---------Offline test start----------"
> for i in 1 2 3
> do
>     date
>     ethtool -t p4p4 offline
> done
>
> Output:
>
> ---------OS Information---------
> Linux siva-dev 4.2.0-rc4+ #1 SMP Thu Aug 13 20:24:11 IST 2015 x86_64 
> x86_64 x86_64 GNU/Linux
> ----------Card Information----------
> 03:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
> Gigabit Ethernet PCIe (rev 01)
> 03:00.1 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
> Gigabit Ethernet PCIe (rev 01)
> 03:00.2 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
> Gigabit Ethernet PCIe (rev 01)
> 03:00.3 Ethernet controller: Broadcom Corporation NetXtreme BCM5719 
> Gigabit Ethernet PCIe (rev 01)
> ----------Interface information------
> driver: tg3
> version: 3.137
> firmware-version: 5719-v1.41 NCSI v1.3.6.0
> bus-info: 0000:03:00.3
> supports-statistics: yes
> supports-test: yes
> supports-eeprom-access: yes
> supports-register-dump: yes
> supports-priv-flags: no
> ---------Offline test start----------
> Thu Aug 13 22:05:59 IST 2015
> The test result is PASS
> The test extra info:
> nvram test        (online)      0
> link test         (online)      0
> register test     (offline)     0
> memory test       (offline)     0
> mac loopback test (offline)     0
> phy loopback test (offline)     0
> ext loopback test (offline)     0
> interrupt test    (offline)     0
>
> Thu Aug 13 22:06:00 IST 2015
> The test result is PASS
> The test extra info:
> nvram test        (online)      0
> link test         (online)      0
> register test     (offline)     0
> memory test       (offline)     0
> mac loopback test (offline)     0
> phy loopback test (offline)     0
> ext loopback test (offline)     0
> interrupt test    (offline)     0
>
> Thu Aug 13 22:06:05 IST 2015
> The test result is PASS
> The test extra info:
> nvram test        (online)      0
> link test         (online)      0
> register test     (offline)     0
> memory test       (offline)     0
> mac loopback test (offline)     0
> phy loopback test (offline)     0
> ext loopback test (offline)     0
> interrupt test    (offline)     0
>
> Please check your test environment.
>
>> Thanks,
>> Doug
>>
>> On 08/11/2015 03:31 PM, Michael Chan wrote:
>>> On Tue, 2015-08-11 at 14:24 -0500, Douglas Miller wrote:
>>>> Yes, the "wrap plugs" are the loopback cables/plugs. It is my
>>>> understanding that the "offline" tests do not require anything to be
>>>> plugged into the ports, as they do not in any way touch the "external"
>>>> port. They perform an "internal loopback" test which does not 
>>>> depend on
>>>> any external connection.
>>> Correct.
>>>
>>>>   From what I can tell, the only difference between "offline" and
>>>> "external_lb" is that "external_lb" performs the external loopback
>>>> tests, *in addition to* all the tests done for "offline".
>>> Correct.
>>>
>>>> This would
>>>> imply that the only tests that depend on anything connected to the
>>>> physical port is "external_lb", and there is no requirement that the
>>>> wrap plugs be removed/replaced in order to run "offline" tests.
>>> When you do external loopback test, we skip the link test because 
>>> you no
>>> longer have normal connection to the network.  You now use a special
>>> loopback cable, which will fail the link up test because the link up
>>> test assumes connection to the network using normal cable.
>>>
>>>> In the case I was debugging, wrap plugs were installed because the 
>>>> ports
>>>> were, later, being tested in an "external loopback" way.
>>>>
>>>> What I am observing is that it takes about 20 seconds for the 
>>>> kernel to
>>>> declare that the link is up, after running the "offline" or
>>>> "external_lb" test. In the case of "offline" I cannot run the test 
>>>> again
>>>> until the kernel declares the link up. In the case of "external_lb" I
>>>> can run the test again immediately and it passes.
>>> As stated earlier, because we skip the link test when we are performing
>>> external_lb.
>>>
>>> So, you should always do ethtool -t <dev> external_lb if you have a
>>> loopback cable connected.  We will perform the external loopback test
>>> and skip the link test.
>>>
>>> If you don't have an external loopback cable connected, you should run
>>> ethtool -t <dev> offline.  It will not do the external loopback test 
>>> and
>>> will do the link test for proper link up with the network.
>>>
>>>> This suggests to me
>>>> that the "external_lb" case (again, it is a superset of "offline") is
>>>> performing some configuration on the port that allows the subsequent
>>>> test to work. The one significant difference between "offline" and
>>>> "external_lb" is that "external_lb" performs the
>>>> "tg3_phy_lpbk_set(tp, 0, true);" changes to configuration (immediately
>>>> prior to running the loopback tests again). I believe this call is to
>>>> switch from "internal loopback" to "normal", in order to leverage the
>>>> wrap plugs and perform the external loopback tests. But this call 
>>>> is not
>>>> made for "offline" and I am wondering if that leaves the port in a 
>>>> state
>>>> where it cannot be used until the kernel completes the "link up".
>>>>
>>>>
>>
>