Discovering which PHY caused the CHANGE

Johnson, Stephen B. sjohnson at
Fri Jan 31 14:29:26 PST 2003

* From the T10 Reflector (t10 at, posted by:
* "Johnson, Stephen B." <sjohnson at>

Link Reset can occur on loss of dword sync and other causes. This will cause
an expander to broadcast CHANGE as it should.
If a SATA device is attached to the culprit PHY, the command set will be
As an initiator I would like to know which drives command set was cleared
before IO's start timing out.

Using SMP commands how does the initiator know which PHY caused the CHANGE
if the link rate has not changed?

I can't seem to find anything definitive using SMP requests.

The REPORT GENERAL gives the EXPANDER CHANGE COUNT, so we know which
expander broadcast the change.

I don't see any fields in the DISCOVER response that help.
I don't see any fields in the REPORT PHY SATA that help.

but I don't think that was the intent of this request and it does not cover
all the cases.

SAS drives could possibly continue along since the command set is not
cleared and link rate hasn't changed. 
But, it will still kick off a discovery that does not find anything. This is
OK behavior.

So, what we really could use is a 16 bit PHY CHANGE COUNT field in the
DISCOVER response that behaves similar to the EXPANDER CHANGE COUNT.

Steve Johnson
LSI Logic
719 533 7511
sjohnson at

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