[U-Boot] [PATCH] tsec: Wait for auto-negotiation to complete without link

[Jerry Van Baren]

Andy Fleming wrote:
> On Fri, Feb 6, 2009 at 7:32 AM, Jerry Van Baren <gerald.vanbaren at ge.com> wrote:
>> Peter Tyser wrote:
> 
>>>> The problem is that you don't always know which interface you have
>>>> hooked up.  So u-boot tries the one set in ethact, and then the next,
>>>> etc.  With the old method, the penalty for being wrong was quite high.
>>>>  I hadn't run into an issue with the link not being up.  Why don't we
>>>> look up the spec, and find out the maximum time we'd have to wait for
>>>> that to happen.  That way we get the best of both worlds.  My sense is
>>>> that the link comes up fast, but autonegotiation potentially takes a
>>>> while.
>> 2 seconds minimum, it is written in the autonegotiation spec.  If you add
>> the spec-required minimum times for each step of the dance, it is 2 seconds.
>>  It could take longer, but I've never seen anything but 2 seconds.
> 
> Could you point me at where in the spec it says this?  I've been
> digging around in it, and found nothing concrete so far.

I've been sweating bullets just *knowing* someone was going to call me 
on this.  Oh man, I am ***SO*** lucky... I had to dig back to October 
2002 to find it, but find it I did.  :-) :-) :-)

My experience is that "The second case assumes that the far end link 
partner fully supports Auto-Negotiation:" / "Min spec" time is what 
occurs.  I've never seen a PHY take anything other than bang-on 2 
seconds (OK, 2.054 seconds).

IIRC, the "min spec" time is the minimum time a PHY is allowed to take 
for autonegotiation.  The "max spec" time is the maximum time the PHY is 
allowed to take for autonegotiation.  The PHY *has* everything it needs 
to know by the "min spec" time, which is why all PHYs (that I've ever 
used) take exactly 2 seconds for autonegotiation.

If you wanted to be safer than my semi-empirical 2 second number, 2.8 
(round up to 3?) seconds is probably a good choice.

Note that the first case mentioned below is oddball in that the far end 
doesn't support autonegotiation.  In real life, you are probably screwed 
in this case regardless of the time it takes for autonegotiation to fail.

I recall verifying the DP83840 calculations against chapter 28 of the 
IEEE 802.3u and I *clearly* recall not wanting to go back there ever 
again.  If you doubt the numbers, *you* can go there.  ;-)

Enjoy,
gvb

------------------------------------------------------------------
Worst case auto-negotiate times per IEEE.
------------------------------------------------------------------

Quote from National Instrument's DP83840A Datasheet:
==================================================================
3.9.6 Auto-Negotiation Complete Time

This section describes the amount of time required to complete an
Auto-Negotiation cycle for the 840A. These times are defined for two cases.

The first case assumes that the far end link partner does not support
Auto-Negotiation and is either a fixed 10M or 100M implementation.

Timer			Min spec	Max spec	DP83840A
-----			--------	--------	--------
Break link		1200ms		1500ms		1300ms
Autoneg wait		 500ms		1000ms		 750ms
Link fail inhibit	 750ms		1000ms		 800ms
------------------------------------------------------------------
Total			1700-2450ms	2500-3500ms	2050-2850ms


The second case assumes that the far end link partner fully
supports Auto-Negotiation:

Timer			Min spec	Max spec	DP83840A
-----			--------	--------	--------
Break link		1200ms		1500ms		1300ms
FLP bursts		 104ms		 312ms		 200ms
Link fail inhibit	 750ms		1000ms		 800ms
------------------------------------------------------------------
Total			1304-2054ms	1812-2812ms	1500-2300ms

Refer to chapter 28 of the IEEE 802.3u standard for a full description 
of  the individual timers related to Auto-Negotiation.
==========================================================================

Notes:
* The minimum time in the "Total" lines is if "Link fail inhibit" is not
necessary.  The maximum is the sum of all three times in the column.

* Assuming "Link fail inhibit" doesn't occur, the "Break link" dominates
the time required.

* Our experience is that the PHYs can be configured to start 
auto-negotiating on application of power.  This allows the 
auto-negotiation to occur in parallel with the processor start up code. 
  This is helpful, but 2 seconds is still a long time.

* The FLP pulse width is 100nSec (10MHz fundamental frequency, probably
square edges).